linux/fs/open.c

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// SPDX-License-Identifier: GPL-2.0-only
/*
* linux/fs/open.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
*/
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/fsnotify.h>
#include <linux/module.h>
#include <linux/tty.h>
#include <linux/namei.h>
#include <linux/backing-dev.h>
#include <linux/capability.h>
#include <linux/securebits.h>
#include <linux/security.h>
#include <linux/mount.h>
[PATCH] vfs: *at functions: core Here is a series of patches which introduce in total 13 new system calls which take a file descriptor/filename pair instead of a single file name. These functions, openat etc, have been discussed on numerous occasions. They are needed to implement race-free filesystem traversal, they are necessary to implement a virtual per-thread current working directory (think multi-threaded backup software), etc. We have in glibc today implementations of the interfaces which use the /proc/self/fd magic. But this code is rather expensive. Here are some results (similar to what Jim Meyering posted before). The test creates a deep directory hierarchy on a tmpfs filesystem. Then rm -fr is used to remove all directories. Without syscall support I get this: real 0m31.921s user 0m0.688s sys 0m31.234s With syscall support the results are much better: real 0m20.699s user 0m0.536s sys 0m20.149s The interfaces are for obvious reasons currently not much used. But they'll be used. coreutils (and Jeff's posixutils) are already using them. Furthermore, code like ftw/fts in libc (maybe even glob) will also start using them. I expect a patch to make follow soon. Every program which is walking the filesystem tree will benefit. Signed-off-by: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@ftp.linux.org.uk> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-19 04:43:53 +03:00
#include <linux/fcntl.h>
include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h percpu.h is included by sched.h and module.h and thus ends up being included when building most .c files. percpu.h includes slab.h which in turn includes gfp.h making everything defined by the two files universally available and complicating inclusion dependencies. percpu.h -> slab.h dependency is about to be removed. Prepare for this change by updating users of gfp and slab facilities include those headers directly instead of assuming availability. As this conversion needs to touch large number of source files, the following script is used as the basis of conversion. http://userweb.kernel.org/~tj/misc/slabh-sweep.py The script does the followings. * Scan files for gfp and slab usages and update includes such that only the necessary includes are there. ie. if only gfp is used, gfp.h, if slab is used, slab.h. * When the script inserts a new include, it looks at the include blocks and try to put the new include such that its order conforms to its surrounding. It's put in the include block which contains core kernel includes, in the same order that the rest are ordered - alphabetical, Christmas tree, rev-Xmas-tree or at the end if there doesn't seem to be any matching order. * If the script can't find a place to put a new include (mostly because the file doesn't have fitting include block), it prints out an error message indicating which .h file needs to be added to the file. The conversion was done in the following steps. 1. The initial automatic conversion of all .c files updated slightly over 4000 files, deleting around 700 includes and adding ~480 gfp.h and ~3000 slab.h inclusions. The script emitted errors for ~400 files. 2. Each error was manually checked. Some didn't need the inclusion, some needed manual addition while adding it to implementation .h or embedding .c file was more appropriate for others. This step added inclusions to around 150 files. 3. The script was run again and the output was compared to the edits from #2 to make sure no file was left behind. 4. Several build tests were done and a couple of problems were fixed. e.g. lib/decompress_*.c used malloc/free() wrappers around slab APIs requiring slab.h to be added manually. 5. The script was run on all .h files but without automatically editing them as sprinkling gfp.h and slab.h inclusions around .h files could easily lead to inclusion dependency hell. Most gfp.h inclusion directives were ignored as stuff from gfp.h was usually wildly available and often used in preprocessor macros. Each slab.h inclusion directive was examined and added manually as necessary. 6. percpu.h was updated not to include slab.h. 7. Build test were done on the following configurations and failures were fixed. CONFIG_GCOV_KERNEL was turned off for all tests (as my distributed build env didn't work with gcov compiles) and a few more options had to be turned off depending on archs to make things build (like ipr on powerpc/64 which failed due to missing writeq). * x86 and x86_64 UP and SMP allmodconfig and a custom test config. * powerpc and powerpc64 SMP allmodconfig * sparc and sparc64 SMP allmodconfig * ia64 SMP allmodconfig * s390 SMP allmodconfig * alpha SMP allmodconfig * um on x86_64 SMP allmodconfig 8. percpu.h modifications were reverted so that it could be applied as a separate patch and serve as bisection point. Given the fact that I had only a couple of failures from tests on step 6, I'm fairly confident about the coverage of this conversion patch. If there is a breakage, it's likely to be something in one of the arch headers which should be easily discoverable easily on most builds of the specific arch. Signed-off-by: Tejun Heo <tj@kernel.org> Guess-its-ok-by: Christoph Lameter <cl@linux-foundation.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
2010-03-24 11:04:11 +03:00
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/fs.h>
#include <linux/personality.h>
#include <linux/pagemap.h>
#include <linux/syscalls.h>
#include <linux/rcupdate.h>
#include <linux/audit.h>
sys_fallocate() implementation on i386, x86_64 and powerpc fallocate() is a new system call being proposed here which will allow applications to preallocate space to any file(s) in a file system. Each file system implementation that wants to use this feature will need to support an inode operation called ->fallocate(). Applications can use this feature to avoid fragmentation to certain level and thus get faster access speed. With preallocation, applications also get a guarantee of space for particular file(s) - even if later the the system becomes full. Currently, glibc provides an interface called posix_fallocate() which can be used for similar cause. Though this has the advantage of working on all file systems, but it is quite slow (since it writes zeroes to each block that has to be preallocated). Without a doubt, file systems can do this more efficiently within the kernel, by implementing the proposed fallocate() system call. It is expected that posix_fallocate() will be modified to call this new system call first and incase the kernel/filesystem does not implement it, it should fall back to the current implementation of writing zeroes to the new blocks. ToDos: 1. Implementation on other architectures (other than i386, x86_64, and ppc). Patches for s390(x) and ia64 are already available from previous posts, but it was decided that they should be added later once fallocate is in the mainline. Hence not including those patches in this take. 2. Changes to glibc, a) to support fallocate() system call b) to make posix_fallocate() and posix_fallocate64() call fallocate() Signed-off-by: Amit Arora <aarora@in.ibm.com>
2007-07-18 05:42:44 +04:00
#include <linux/falloc.h>
#include <linux/fs_struct.h>
#include <linux/ima.h>
#include <linux/dnotify.h>
#include <linux/compat.h>
#include <linux/mnt_idmapping.h>
#include <linux/filelock.h>
#include "internal.h"
int do_truncate(struct mnt_idmap *idmap, struct dentry *dentry,
loff_t length, unsigned int time_attrs, struct file *filp)
{
int ret;
struct iattr newattrs;
/* Not pretty: "inode->i_size" shouldn't really be signed. But it is. */
if (length < 0)
return -EINVAL;
newattrs.ia_size = length;
newattrs.ia_valid = ATTR_SIZE | time_attrs;
if (filp) {
newattrs.ia_file = filp;
newattrs.ia_valid |= ATTR_FILE;
}
/* Remove suid, sgid, and file capabilities on truncate too */
ret = dentry_needs_remove_privs(idmap, dentry);
if (ret < 0)
return ret;
if (ret)
newattrs.ia_valid |= ret | ATTR_FORCE;
inode_lock(dentry->d_inode);
/* Note any delegations or leases have already been broken: */
ret = notify_change(idmap, dentry, &newattrs, NULL);
inode_unlock(dentry->d_inode);
return ret;
}
long vfs_truncate(const struct path *path, loff_t length)
{
struct mnt_idmap *idmap;
struct inode *inode;
long error;
inode = path->dentry->d_inode;
/* For directories it's -EISDIR, for other non-regulars - -EINVAL */
if (S_ISDIR(inode->i_mode))
return -EISDIR;
if (!S_ISREG(inode->i_mode))
return -EINVAL;
error = mnt_want_write(path->mnt);
if (error)
goto out;
idmap = mnt_idmap(path->mnt);
error = inode_permission(idmap, inode, MAY_WRITE);
if (error)
goto mnt_drop_write_and_out;
error = -EPERM;
if (IS_APPEND(inode))
goto mnt_drop_write_and_out;
error = get_write_access(inode);
if (error)
goto mnt_drop_write_and_out;
/*
* Make sure that there are no leases. get_write_access() protects
* against the truncate racing with a lease-granting setlease().
*/
error = break_lease(inode, O_WRONLY);
if (error)
goto put_write_and_out;
error = security_path_truncate(path);
if (!error)
error = do_truncate(idmap, path->dentry, length, 0, NULL);
put_write_and_out:
put_write_access(inode);
mnt_drop_write_and_out:
mnt_drop_write(path->mnt);
out:
return error;
}
EXPORT_SYMBOL_GPL(vfs_truncate);
long do_sys_truncate(const char __user *pathname, loff_t length)
{
unsigned int lookup_flags = LOOKUP_FOLLOW;
struct path path;
int error;
if (length < 0) /* sorry, but loff_t says... */
return -EINVAL;
retry:
error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
if (!error) {
error = vfs_truncate(&path, length);
path_put(&path);
}
if (retry_estale(error, lookup_flags)) {
lookup_flags |= LOOKUP_REVAL;
goto retry;
}
return error;
}
SYSCALL_DEFINE2(truncate, const char __user *, path, long, length)
{
return do_sys_truncate(path, length);
}
#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE2(truncate, const char __user *, path, compat_off_t, length)
{
return do_sys_truncate(path, length);
}
#endif
long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
{
struct inode *inode;
struct dentry *dentry;
struct fd f;
int error;
error = -EINVAL;
if (length < 0)
goto out;
error = -EBADF;
f = fdget(fd);
if (!f.file)
goto out;
/* explicitly opened as large or we are on 64-bit box */
if (f.file->f_flags & O_LARGEFILE)
small = 0;
dentry = f.file->f_path.dentry;
inode = dentry->d_inode;
error = -EINVAL;
if (!S_ISREG(inode->i_mode) || !(f.file->f_mode & FMODE_WRITE))
goto out_putf;
error = -EINVAL;
/* Cannot ftruncate over 2^31 bytes without large file support */
if (small && length > MAX_NON_LFS)
goto out_putf;
error = -EPERM;
/* Check IS_APPEND on real upper inode */
if (IS_APPEND(file_inode(f.file)))
goto out_putf;
sb_start_write(inode->i_sb);
error = security_file_truncate(f.file);
if (!error)
error = do_truncate(file_mnt_idmap(f.file), dentry, length,
ATTR_MTIME | ATTR_CTIME, f.file);
sb_end_write(inode->i_sb);
out_putf:
fdput(f);
out:
return error;
}
SYSCALL_DEFINE2(ftruncate, unsigned int, fd, unsigned long, length)
{
return do_sys_ftruncate(fd, length, 1);
}
#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE2(ftruncate, unsigned int, fd, compat_ulong_t, length)
{
return do_sys_ftruncate(fd, length, 1);
}
#endif
/* LFS versions of truncate are only needed on 32 bit machines */
#if BITS_PER_LONG == 32
SYSCALL_DEFINE2(truncate64, const char __user *, path, loff_t, length)
{
return do_sys_truncate(path, length);
}
SYSCALL_DEFINE2(ftruncate64, unsigned int, fd, loff_t, length)
{
return do_sys_ftruncate(fd, length, 0);
}
#endif /* BITS_PER_LONG == 32 */
#if defined(CONFIG_COMPAT) && defined(__ARCH_WANT_COMPAT_TRUNCATE64)
COMPAT_SYSCALL_DEFINE3(truncate64, const char __user *, pathname,
compat_arg_u64_dual(length))
{
return ksys_truncate(pathname, compat_arg_u64_glue(length));
}
#endif
#if defined(CONFIG_COMPAT) && defined(__ARCH_WANT_COMPAT_FTRUNCATE64)
COMPAT_SYSCALL_DEFINE3(ftruncate64, unsigned int, fd,
compat_arg_u64_dual(length))
{
return ksys_ftruncate(fd, compat_arg_u64_glue(length));
}
#endif
int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
sys_fallocate() implementation on i386, x86_64 and powerpc fallocate() is a new system call being proposed here which will allow applications to preallocate space to any file(s) in a file system. Each file system implementation that wants to use this feature will need to support an inode operation called ->fallocate(). Applications can use this feature to avoid fragmentation to certain level and thus get faster access speed. With preallocation, applications also get a guarantee of space for particular file(s) - even if later the the system becomes full. Currently, glibc provides an interface called posix_fallocate() which can be used for similar cause. Though this has the advantage of working on all file systems, but it is quite slow (since it writes zeroes to each block that has to be preallocated). Without a doubt, file systems can do this more efficiently within the kernel, by implementing the proposed fallocate() system call. It is expected that posix_fallocate() will be modified to call this new system call first and incase the kernel/filesystem does not implement it, it should fall back to the current implementation of writing zeroes to the new blocks. ToDos: 1. Implementation on other architectures (other than i386, x86_64, and ppc). Patches for s390(x) and ia64 are already available from previous posts, but it was decided that they should be added later once fallocate is in the mainline. Hence not including those patches in this take. 2. Changes to glibc, a) to support fallocate() system call b) to make posix_fallocate() and posix_fallocate64() call fallocate() Signed-off-by: Amit Arora <aarora@in.ibm.com>
2007-07-18 05:42:44 +04:00
{
struct inode *inode = file_inode(file);
long ret;
sys_fallocate() implementation on i386, x86_64 and powerpc fallocate() is a new system call being proposed here which will allow applications to preallocate space to any file(s) in a file system. Each file system implementation that wants to use this feature will need to support an inode operation called ->fallocate(). Applications can use this feature to avoid fragmentation to certain level and thus get faster access speed. With preallocation, applications also get a guarantee of space for particular file(s) - even if later the the system becomes full. Currently, glibc provides an interface called posix_fallocate() which can be used for similar cause. Though this has the advantage of working on all file systems, but it is quite slow (since it writes zeroes to each block that has to be preallocated). Without a doubt, file systems can do this more efficiently within the kernel, by implementing the proposed fallocate() system call. It is expected that posix_fallocate() will be modified to call this new system call first and incase the kernel/filesystem does not implement it, it should fall back to the current implementation of writing zeroes to the new blocks. ToDos: 1. Implementation on other architectures (other than i386, x86_64, and ppc). Patches for s390(x) and ia64 are already available from previous posts, but it was decided that they should be added later once fallocate is in the mainline. Hence not including those patches in this take. 2. Changes to glibc, a) to support fallocate() system call b) to make posix_fallocate() and posix_fallocate64() call fallocate() Signed-off-by: Amit Arora <aarora@in.ibm.com>
2007-07-18 05:42:44 +04:00
if (offset < 0 || len <= 0)
return -EINVAL;
sys_fallocate() implementation on i386, x86_64 and powerpc fallocate() is a new system call being proposed here which will allow applications to preallocate space to any file(s) in a file system. Each file system implementation that wants to use this feature will need to support an inode operation called ->fallocate(). Applications can use this feature to avoid fragmentation to certain level and thus get faster access speed. With preallocation, applications also get a guarantee of space for particular file(s) - even if later the the system becomes full. Currently, glibc provides an interface called posix_fallocate() which can be used for similar cause. Though this has the advantage of working on all file systems, but it is quite slow (since it writes zeroes to each block that has to be preallocated). Without a doubt, file systems can do this more efficiently within the kernel, by implementing the proposed fallocate() system call. It is expected that posix_fallocate() will be modified to call this new system call first and incase the kernel/filesystem does not implement it, it should fall back to the current implementation of writing zeroes to the new blocks. ToDos: 1. Implementation on other architectures (other than i386, x86_64, and ppc). Patches for s390(x) and ia64 are already available from previous posts, but it was decided that they should be added later once fallocate is in the mainline. Hence not including those patches in this take. 2. Changes to glibc, a) to support fallocate() system call b) to make posix_fallocate() and posix_fallocate64() call fallocate() Signed-off-by: Amit Arora <aarora@in.ibm.com>
2007-07-18 05:42:44 +04:00
/* Return error if mode is not supported */
if (mode & ~FALLOC_FL_SUPPORTED_MASK)
return -EOPNOTSUPP;
/* Punch hole and zero range are mutually exclusive */
if ((mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE)) ==
(FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE))
return -EOPNOTSUPP;
/* Punch hole must have keep size set */
if ((mode & FALLOC_FL_PUNCH_HOLE) &&
!(mode & FALLOC_FL_KEEP_SIZE))
return -EOPNOTSUPP;
sys_fallocate() implementation on i386, x86_64 and powerpc fallocate() is a new system call being proposed here which will allow applications to preallocate space to any file(s) in a file system. Each file system implementation that wants to use this feature will need to support an inode operation called ->fallocate(). Applications can use this feature to avoid fragmentation to certain level and thus get faster access speed. With preallocation, applications also get a guarantee of space for particular file(s) - even if later the the system becomes full. Currently, glibc provides an interface called posix_fallocate() which can be used for similar cause. Though this has the advantage of working on all file systems, but it is quite slow (since it writes zeroes to each block that has to be preallocated). Without a doubt, file systems can do this more efficiently within the kernel, by implementing the proposed fallocate() system call. It is expected that posix_fallocate() will be modified to call this new system call first and incase the kernel/filesystem does not implement it, it should fall back to the current implementation of writing zeroes to the new blocks. ToDos: 1. Implementation on other architectures (other than i386, x86_64, and ppc). Patches for s390(x) and ia64 are already available from previous posts, but it was decided that they should be added later once fallocate is in the mainline. Hence not including those patches in this take. 2. Changes to glibc, a) to support fallocate() system call b) to make posix_fallocate() and posix_fallocate64() call fallocate() Signed-off-by: Amit Arora <aarora@in.ibm.com>
2007-07-18 05:42:44 +04:00
/* Collapse range should only be used exclusively. */
if ((mode & FALLOC_FL_COLLAPSE_RANGE) &&
(mode & ~FALLOC_FL_COLLAPSE_RANGE))
return -EINVAL;
/* Insert range should only be used exclusively. */
if ((mode & FALLOC_FL_INSERT_RANGE) &&
(mode & ~FALLOC_FL_INSERT_RANGE))
return -EINVAL;
/* Unshare range should only be used with allocate mode. */
if ((mode & FALLOC_FL_UNSHARE_RANGE) &&
(mode & ~(FALLOC_FL_UNSHARE_RANGE | FALLOC_FL_KEEP_SIZE)))
return -EINVAL;
sys_fallocate() implementation on i386, x86_64 and powerpc fallocate() is a new system call being proposed here which will allow applications to preallocate space to any file(s) in a file system. Each file system implementation that wants to use this feature will need to support an inode operation called ->fallocate(). Applications can use this feature to avoid fragmentation to certain level and thus get faster access speed. With preallocation, applications also get a guarantee of space for particular file(s) - even if later the the system becomes full. Currently, glibc provides an interface called posix_fallocate() which can be used for similar cause. Though this has the advantage of working on all file systems, but it is quite slow (since it writes zeroes to each block that has to be preallocated). Without a doubt, file systems can do this more efficiently within the kernel, by implementing the proposed fallocate() system call. It is expected that posix_fallocate() will be modified to call this new system call first and incase the kernel/filesystem does not implement it, it should fall back to the current implementation of writing zeroes to the new blocks. ToDos: 1. Implementation on other architectures (other than i386, x86_64, and ppc). Patches for s390(x) and ia64 are already available from previous posts, but it was decided that they should be added later once fallocate is in the mainline. Hence not including those patches in this take. 2. Changes to glibc, a) to support fallocate() system call b) to make posix_fallocate() and posix_fallocate64() call fallocate() Signed-off-by: Amit Arora <aarora@in.ibm.com>
2007-07-18 05:42:44 +04:00
if (!(file->f_mode & FMODE_WRITE))
return -EBADF;
/*
* We can only allow pure fallocate on append only files
*/
if ((mode & ~FALLOC_FL_KEEP_SIZE) && IS_APPEND(inode))
return -EPERM;
if (IS_IMMUTABLE(inode))
return -EPERM;
/*
* We cannot allow any fallocate operation on an active swapfile
*/
if (IS_SWAPFILE(inode))
return -ETXTBSY;
sys_fallocate() implementation on i386, x86_64 and powerpc fallocate() is a new system call being proposed here which will allow applications to preallocate space to any file(s) in a file system. Each file system implementation that wants to use this feature will need to support an inode operation called ->fallocate(). Applications can use this feature to avoid fragmentation to certain level and thus get faster access speed. With preallocation, applications also get a guarantee of space for particular file(s) - even if later the the system becomes full. Currently, glibc provides an interface called posix_fallocate() which can be used for similar cause. Though this has the advantage of working on all file systems, but it is quite slow (since it writes zeroes to each block that has to be preallocated). Without a doubt, file systems can do this more efficiently within the kernel, by implementing the proposed fallocate() system call. It is expected that posix_fallocate() will be modified to call this new system call first and incase the kernel/filesystem does not implement it, it should fall back to the current implementation of writing zeroes to the new blocks. ToDos: 1. Implementation on other architectures (other than i386, x86_64, and ppc). Patches for s390(x) and ia64 are already available from previous posts, but it was decided that they should be added later once fallocate is in the mainline. Hence not including those patches in this take. 2. Changes to glibc, a) to support fallocate() system call b) to make posix_fallocate() and posix_fallocate64() call fallocate() Signed-off-by: Amit Arora <aarora@in.ibm.com>
2007-07-18 05:42:44 +04:00
/*
* Revalidate the write permissions, in case security policy has
* changed since the files were opened.
*/
ret = security_file_permission(file, MAY_WRITE);
if (ret)
return ret;
sys_fallocate() implementation on i386, x86_64 and powerpc fallocate() is a new system call being proposed here which will allow applications to preallocate space to any file(s) in a file system. Each file system implementation that wants to use this feature will need to support an inode operation called ->fallocate(). Applications can use this feature to avoid fragmentation to certain level and thus get faster access speed. With preallocation, applications also get a guarantee of space for particular file(s) - even if later the the system becomes full. Currently, glibc provides an interface called posix_fallocate() which can be used for similar cause. Though this has the advantage of working on all file systems, but it is quite slow (since it writes zeroes to each block that has to be preallocated). Without a doubt, file systems can do this more efficiently within the kernel, by implementing the proposed fallocate() system call. It is expected that posix_fallocate() will be modified to call this new system call first and incase the kernel/filesystem does not implement it, it should fall back to the current implementation of writing zeroes to the new blocks. ToDos: 1. Implementation on other architectures (other than i386, x86_64, and ppc). Patches for s390(x) and ia64 are already available from previous posts, but it was decided that they should be added later once fallocate is in the mainline. Hence not including those patches in this take. 2. Changes to glibc, a) to support fallocate() system call b) to make posix_fallocate() and posix_fallocate64() call fallocate() Signed-off-by: Amit Arora <aarora@in.ibm.com>
2007-07-18 05:42:44 +04:00
if (S_ISFIFO(inode->i_mode))
return -ESPIPE;
sys_fallocate() implementation on i386, x86_64 and powerpc fallocate() is a new system call being proposed here which will allow applications to preallocate space to any file(s) in a file system. Each file system implementation that wants to use this feature will need to support an inode operation called ->fallocate(). Applications can use this feature to avoid fragmentation to certain level and thus get faster access speed. With preallocation, applications also get a guarantee of space for particular file(s) - even if later the the system becomes full. Currently, glibc provides an interface called posix_fallocate() which can be used for similar cause. Though this has the advantage of working on all file systems, but it is quite slow (since it writes zeroes to each block that has to be preallocated). Without a doubt, file systems can do this more efficiently within the kernel, by implementing the proposed fallocate() system call. It is expected that posix_fallocate() will be modified to call this new system call first and incase the kernel/filesystem does not implement it, it should fall back to the current implementation of writing zeroes to the new blocks. ToDos: 1. Implementation on other architectures (other than i386, x86_64, and ppc). Patches for s390(x) and ia64 are already available from previous posts, but it was decided that they should be added later once fallocate is in the mainline. Hence not including those patches in this take. 2. Changes to glibc, a) to support fallocate() system call b) to make posix_fallocate() and posix_fallocate64() call fallocate() Signed-off-by: Amit Arora <aarora@in.ibm.com>
2007-07-18 05:42:44 +04:00
if (S_ISDIR(inode->i_mode))
return -EISDIR;
if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode))
return -ENODEV;
sys_fallocate() implementation on i386, x86_64 and powerpc fallocate() is a new system call being proposed here which will allow applications to preallocate space to any file(s) in a file system. Each file system implementation that wants to use this feature will need to support an inode operation called ->fallocate(). Applications can use this feature to avoid fragmentation to certain level and thus get faster access speed. With preallocation, applications also get a guarantee of space for particular file(s) - even if later the the system becomes full. Currently, glibc provides an interface called posix_fallocate() which can be used for similar cause. Though this has the advantage of working on all file systems, but it is quite slow (since it writes zeroes to each block that has to be preallocated). Without a doubt, file systems can do this more efficiently within the kernel, by implementing the proposed fallocate() system call. It is expected that posix_fallocate() will be modified to call this new system call first and incase the kernel/filesystem does not implement it, it should fall back to the current implementation of writing zeroes to the new blocks. ToDos: 1. Implementation on other architectures (other than i386, x86_64, and ppc). Patches for s390(x) and ia64 are already available from previous posts, but it was decided that they should be added later once fallocate is in the mainline. Hence not including those patches in this take. 2. Changes to glibc, a) to support fallocate() system call b) to make posix_fallocate() and posix_fallocate64() call fallocate() Signed-off-by: Amit Arora <aarora@in.ibm.com>
2007-07-18 05:42:44 +04:00
/* Check for wrap through zero too */
if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
return -EFBIG;
sys_fallocate() implementation on i386, x86_64 and powerpc fallocate() is a new system call being proposed here which will allow applications to preallocate space to any file(s) in a file system. Each file system implementation that wants to use this feature will need to support an inode operation called ->fallocate(). Applications can use this feature to avoid fragmentation to certain level and thus get faster access speed. With preallocation, applications also get a guarantee of space for particular file(s) - even if later the the system becomes full. Currently, glibc provides an interface called posix_fallocate() which can be used for similar cause. Though this has the advantage of working on all file systems, but it is quite slow (since it writes zeroes to each block that has to be preallocated). Without a doubt, file systems can do this more efficiently within the kernel, by implementing the proposed fallocate() system call. It is expected that posix_fallocate() will be modified to call this new system call first and incase the kernel/filesystem does not implement it, it should fall back to the current implementation of writing zeroes to the new blocks. ToDos: 1. Implementation on other architectures (other than i386, x86_64, and ppc). Patches for s390(x) and ia64 are already available from previous posts, but it was decided that they should be added later once fallocate is in the mainline. Hence not including those patches in this take. 2. Changes to glibc, a) to support fallocate() system call b) to make posix_fallocate() and posix_fallocate64() call fallocate() Signed-off-by: Amit Arora <aarora@in.ibm.com>
2007-07-18 05:42:44 +04:00
if (!file->f_op->fallocate)
return -EOPNOTSUPP;
sys_fallocate() implementation on i386, x86_64 and powerpc fallocate() is a new system call being proposed here which will allow applications to preallocate space to any file(s) in a file system. Each file system implementation that wants to use this feature will need to support an inode operation called ->fallocate(). Applications can use this feature to avoid fragmentation to certain level and thus get faster access speed. With preallocation, applications also get a guarantee of space for particular file(s) - even if later the the system becomes full. Currently, glibc provides an interface called posix_fallocate() which can be used for similar cause. Though this has the advantage of working on all file systems, but it is quite slow (since it writes zeroes to each block that has to be preallocated). Without a doubt, file systems can do this more efficiently within the kernel, by implementing the proposed fallocate() system call. It is expected that posix_fallocate() will be modified to call this new system call first and incase the kernel/filesystem does not implement it, it should fall back to the current implementation of writing zeroes to the new blocks. ToDos: 1. Implementation on other architectures (other than i386, x86_64, and ppc). Patches for s390(x) and ia64 are already available from previous posts, but it was decided that they should be added later once fallocate is in the mainline. Hence not including those patches in this take. 2. Changes to glibc, a) to support fallocate() system call b) to make posix_fallocate() and posix_fallocate64() call fallocate() Signed-off-by: Amit Arora <aarora@in.ibm.com>
2007-07-18 05:42:44 +04:00
file_start_write(file);
ret = file->f_op->fallocate(file, mode, offset, len);
fallocate: create FAN_MODIFY and IN_MODIFY events The fanotify and the inotify API can be used to monitor changes of the file system. System call fallocate() modifies files. Hence it should trigger the corresponding fanotify (FAN_MODIFY) and inotify (IN_MODIFY) events. The most interesting case is FALLOC_FL_COLLAPSE_RANGE because this value allows to create arbitrary file content from random data. This patch adds the missing call to fsnotify_modify(). The FAN_MODIFY and IN_MODIFY event will be created when fallocate() succeeds. It will even be created if the file length remains unchanged, e.g. when calling fanotify with flag FALLOC_FL_KEEP_SIZE. This logic was primarily chosen to keep the coding simple. It resembles the logic of the write() system call. When we call write() we always create a FAN_MODIFY event, even in the case of overwriting with identical data. Events FAN_MODIFY and IN_MODIFY do not provide any guarantee that data was actually changed. Furthermore even if if the filesize remains unchanged, fallocate() may influence whether a subsequent write() will succeed and hence the fallocate() call may be considered a modification. The fallocate(2) man page teaches: After a successful call, subsequent writes into the range specified by offset and len are guaranteed not to fail because of lack of disk space. So calling fallocate(fd, FALLOC_FL_KEEP_SIZE, offset, len) may result in different outcomes of a subsequent write depending on the values of offset and len. Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Jan Kara <jack@suse.cz> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Eric Paris <eparis@parisplace.org> Cc: John McCutchan <john@johnmccutchan.com> Cc: Robert Love <rlove@rlove.org> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Theodore Ts'o <tytso@mit.edu> Cc: Dave Chinner <david@fromorbit.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-12-13 03:58:34 +03:00
/*
* Create inotify and fanotify events.
*
* To keep the logic simple always create events if fallocate succeeds.
* This implies that events are even created if the file size remains
* unchanged, e.g. when using flag FALLOC_FL_KEEP_SIZE.
*/
if (ret == 0)
fsnotify_modify(file);
file_end_write(file);
return ret;
}
EXPORT_SYMBOL_GPL(vfs_fallocate);
int ksys_fallocate(int fd, int mode, loff_t offset, loff_t len)
{
struct fd f = fdget(fd);
int error = -EBADF;
if (f.file) {
error = vfs_fallocate(f.file, mode, offset, len);
fdput(f);
}
return error;
sys_fallocate() implementation on i386, x86_64 and powerpc fallocate() is a new system call being proposed here which will allow applications to preallocate space to any file(s) in a file system. Each file system implementation that wants to use this feature will need to support an inode operation called ->fallocate(). Applications can use this feature to avoid fragmentation to certain level and thus get faster access speed. With preallocation, applications also get a guarantee of space for particular file(s) - even if later the the system becomes full. Currently, glibc provides an interface called posix_fallocate() which can be used for similar cause. Though this has the advantage of working on all file systems, but it is quite slow (since it writes zeroes to each block that has to be preallocated). Without a doubt, file systems can do this more efficiently within the kernel, by implementing the proposed fallocate() system call. It is expected that posix_fallocate() will be modified to call this new system call first and incase the kernel/filesystem does not implement it, it should fall back to the current implementation of writing zeroes to the new blocks. ToDos: 1. Implementation on other architectures (other than i386, x86_64, and ppc). Patches for s390(x) and ia64 are already available from previous posts, but it was decided that they should be added later once fallocate is in the mainline. Hence not including those patches in this take. 2. Changes to glibc, a) to support fallocate() system call b) to make posix_fallocate() and posix_fallocate64() call fallocate() Signed-off-by: Amit Arora <aarora@in.ibm.com>
2007-07-18 05:42:44 +04:00
}
SYSCALL_DEFINE4(fallocate, int, fd, int, mode, loff_t, offset, loff_t, len)
{
return ksys_fallocate(fd, mode, offset, len);
}
#if defined(CONFIG_COMPAT) && defined(__ARCH_WANT_COMPAT_FALLOCATE)
COMPAT_SYSCALL_DEFINE6(fallocate, int, fd, int, mode, compat_arg_u64_dual(offset),
compat_arg_u64_dual(len))
{
return ksys_fallocate(fd, mode, compat_arg_u64_glue(offset),
compat_arg_u64_glue(len));
}
#endif
/*
* access() needs to use the real uid/gid, not the effective uid/gid.
* We do this by temporarily clearing all FS-related capabilities and
* switching the fsuid/fsgid around to the real ones.
*
* Creating new credentials is expensive, so we try to skip doing it,
* which we can if the result would match what we already got.
*/
static bool access_need_override_creds(int flags)
{
const struct cred *cred;
if (flags & AT_EACCESS)
return false;
cred = current_cred();
if (!uid_eq(cred->fsuid, cred->uid) ||
!gid_eq(cred->fsgid, cred->gid))
return true;
if (!issecure(SECURE_NO_SETUID_FIXUP)) {
kuid_t root_uid = make_kuid(cred->user_ns, 0);
if (!uid_eq(cred->uid, root_uid)) {
if (!cap_isclear(cred->cap_effective))
return true;
} else {
if (!cap_isidentical(cred->cap_effective,
cred->cap_permitted))
return true;
}
}
return false;
}
static const struct cred *access_override_creds(void)
{
CRED: Inaugurate COW credentials Inaugurate copy-on-write credentials management. This uses RCU to manage the credentials pointer in the task_struct with respect to accesses by other tasks. A process may only modify its own credentials, and so does not need locking to access or modify its own credentials. A mutex (cred_replace_mutex) is added to the task_struct to control the effect of PTRACE_ATTACHED on credential calculations, particularly with respect to execve(). With this patch, the contents of an active credentials struct may not be changed directly; rather a new set of credentials must be prepared, modified and committed using something like the following sequence of events: struct cred *new = prepare_creds(); int ret = blah(new); if (ret < 0) { abort_creds(new); return ret; } return commit_creds(new); There are some exceptions to this rule: the keyrings pointed to by the active credentials may be instantiated - keyrings violate the COW rule as managing COW keyrings is tricky, given that it is possible for a task to directly alter the keys in a keyring in use by another task. To help enforce this, various pointers to sets of credentials, such as those in the task_struct, are declared const. The purpose of this is compile-time discouragement of altering credentials through those pointers. Once a set of credentials has been made public through one of these pointers, it may not be modified, except under special circumstances: (1) Its reference count may incremented and decremented. (2) The keyrings to which it points may be modified, but not replaced. The only safe way to modify anything else is to create a replacement and commit using the functions described in Documentation/credentials.txt (which will be added by a later patch). This patch and the preceding patches have been tested with the LTP SELinux testsuite. This patch makes several logical sets of alteration: (1) execve(). This now prepares and commits credentials in various places in the security code rather than altering the current creds directly. (2) Temporary credential overrides. do_coredump() and sys_faccessat() now prepare their own credentials and temporarily override the ones currently on the acting thread, whilst preventing interference from other threads by holding cred_replace_mutex on the thread being dumped. This will be replaced in a future patch by something that hands down the credentials directly to the functions being called, rather than altering the task's objective credentials. (3) LSM interface. A number of functions have been changed, added or removed: (*) security_capset_check(), ->capset_check() (*) security_capset_set(), ->capset_set() Removed in favour of security_capset(). (*) security_capset(), ->capset() New. This is passed a pointer to the new creds, a pointer to the old creds and the proposed capability sets. It should fill in the new creds or return an error. All pointers, barring the pointer to the new creds, are now const. (*) security_bprm_apply_creds(), ->bprm_apply_creds() Changed; now returns a value, which will cause the process to be killed if it's an error. (*) security_task_alloc(), ->task_alloc_security() Removed in favour of security_prepare_creds(). (*) security_cred_free(), ->cred_free() New. Free security data attached to cred->security. (*) security_prepare_creds(), ->cred_prepare() New. Duplicate any security data attached to cred->security. (*) security_commit_creds(), ->cred_commit() New. Apply any security effects for the upcoming installation of new security by commit_creds(). (*) security_task_post_setuid(), ->task_post_setuid() Removed in favour of security_task_fix_setuid(). (*) security_task_fix_setuid(), ->task_fix_setuid() Fix up the proposed new credentials for setuid(). This is used by cap_set_fix_setuid() to implicitly adjust capabilities in line with setuid() changes. Changes are made to the new credentials, rather than the task itself as in security_task_post_setuid(). (*) security_task_reparent_to_init(), ->task_reparent_to_init() Removed. Instead the task being reparented to init is referred directly to init's credentials. NOTE! This results in the loss of some state: SELinux's osid no longer records the sid of the thread that forked it. (*) security_key_alloc(), ->key_alloc() (*) security_key_permission(), ->key_permission() Changed. These now take cred pointers rather than task pointers to refer to the security context. (4) sys_capset(). This has been simplified and uses less locking. The LSM functions it calls have been merged. (5) reparent_to_kthreadd(). This gives the current thread the same credentials as init by simply using commit_thread() to point that way. (6) __sigqueue_alloc() and switch_uid() __sigqueue_alloc() can't stop the target task from changing its creds beneath it, so this function gets a reference to the currently applicable user_struct which it then passes into the sigqueue struct it returns if successful. switch_uid() is now called from commit_creds(), and possibly should be folded into that. commit_creds() should take care of protecting __sigqueue_alloc(). (7) [sg]et[ug]id() and co and [sg]et_current_groups. The set functions now all use prepare_creds(), commit_creds() and abort_creds() to build and check a new set of credentials before applying it. security_task_set[ug]id() is called inside the prepared section. This guarantees that nothing else will affect the creds until we've finished. The calling of set_dumpable() has been moved into commit_creds(). Much of the functionality of set_user() has been moved into commit_creds(). The get functions all simply access the data directly. (8) security_task_prctl() and cap_task_prctl(). security_task_prctl() has been modified to return -ENOSYS if it doesn't want to handle a function, or otherwise return the return value directly rather than through an argument. Additionally, cap_task_prctl() now prepares a new set of credentials, even if it doesn't end up using it. (9) Keyrings. A number of changes have been made to the keyrings code: (a) switch_uid_keyring(), copy_keys(), exit_keys() and suid_keys() have all been dropped and built in to the credentials functions directly. They may want separating out again later. (b) key_alloc() and search_process_keyrings() now take a cred pointer rather than a task pointer to specify the security context. (c) copy_creds() gives a new thread within the same thread group a new thread keyring if its parent had one, otherwise it discards the thread keyring. (d) The authorisation key now points directly to the credentials to extend the search into rather pointing to the task that carries them. (e) Installing thread, process or session keyrings causes a new set of credentials to be created, even though it's not strictly necessary for process or session keyrings (they're shared). (10) Usermode helper. The usermode helper code now carries a cred struct pointer in its subprocess_info struct instead of a new session keyring pointer. This set of credentials is derived from init_cred and installed on the new process after it has been cloned. call_usermodehelper_setup() allocates the new credentials and call_usermodehelper_freeinfo() discards them if they haven't been used. A special cred function (prepare_usermodeinfo_creds()) is provided specifically for call_usermodehelper_setup() to call. call_usermodehelper_setkeys() adjusts the credentials to sport the supplied keyring as the new session keyring. (11) SELinux. SELinux has a number of changes, in addition to those to support the LSM interface changes mentioned above: (a) selinux_setprocattr() no longer does its check for whether the current ptracer can access processes with the new SID inside the lock that covers getting the ptracer's SID. Whilst this lock ensures that the check is done with the ptracer pinned, the result is only valid until the lock is released, so there's no point doing it inside the lock. (12) is_single_threaded(). This function has been extracted from selinux_setprocattr() and put into a file of its own in the lib/ directory as join_session_keyring() now wants to use it too. The code in SELinux just checked to see whether a task shared mm_structs with other tasks (CLONE_VM), but that isn't good enough. We really want to know if they're part of the same thread group (CLONE_THREAD). (13) nfsd. The NFS server daemon now has to use the COW credentials to set the credentials it is going to use. It really needs to pass the credentials down to the functions it calls, but it can't do that until other patches in this series have been applied. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: James Morris <jmorris@namei.org> Signed-off-by: James Morris <jmorris@namei.org>
2008-11-14 02:39:23 +03:00
const struct cred *old_cred;
struct cred *override_cred;
CRED: Inaugurate COW credentials Inaugurate copy-on-write credentials management. This uses RCU to manage the credentials pointer in the task_struct with respect to accesses by other tasks. A process may only modify its own credentials, and so does not need locking to access or modify its own credentials. A mutex (cred_replace_mutex) is added to the task_struct to control the effect of PTRACE_ATTACHED on credential calculations, particularly with respect to execve(). With this patch, the contents of an active credentials struct may not be changed directly; rather a new set of credentials must be prepared, modified and committed using something like the following sequence of events: struct cred *new = prepare_creds(); int ret = blah(new); if (ret < 0) { abort_creds(new); return ret; } return commit_creds(new); There are some exceptions to this rule: the keyrings pointed to by the active credentials may be instantiated - keyrings violate the COW rule as managing COW keyrings is tricky, given that it is possible for a task to directly alter the keys in a keyring in use by another task. To help enforce this, various pointers to sets of credentials, such as those in the task_struct, are declared const. The purpose of this is compile-time discouragement of altering credentials through those pointers. Once a set of credentials has been made public through one of these pointers, it may not be modified, except under special circumstances: (1) Its reference count may incremented and decremented. (2) The keyrings to which it points may be modified, but not replaced. The only safe way to modify anything else is to create a replacement and commit using the functions described in Documentation/credentials.txt (which will be added by a later patch). This patch and the preceding patches have been tested with the LTP SELinux testsuite. This patch makes several logical sets of alteration: (1) execve(). This now prepares and commits credentials in various places in the security code rather than altering the current creds directly. (2) Temporary credential overrides. do_coredump() and sys_faccessat() now prepare their own credentials and temporarily override the ones currently on the acting thread, whilst preventing interference from other threads by holding cred_replace_mutex on the thread being dumped. This will be replaced in a future patch by something that hands down the credentials directly to the functions being called, rather than altering the task's objective credentials. (3) LSM interface. A number of functions have been changed, added or removed: (*) security_capset_check(), ->capset_check() (*) security_capset_set(), ->capset_set() Removed in favour of security_capset(). (*) security_capset(), ->capset() New. This is passed a pointer to the new creds, a pointer to the old creds and the proposed capability sets. It should fill in the new creds or return an error. All pointers, barring the pointer to the new creds, are now const. (*) security_bprm_apply_creds(), ->bprm_apply_creds() Changed; now returns a value, which will cause the process to be killed if it's an error. (*) security_task_alloc(), ->task_alloc_security() Removed in favour of security_prepare_creds(). (*) security_cred_free(), ->cred_free() New. Free security data attached to cred->security. (*) security_prepare_creds(), ->cred_prepare() New. Duplicate any security data attached to cred->security. (*) security_commit_creds(), ->cred_commit() New. Apply any security effects for the upcoming installation of new security by commit_creds(). (*) security_task_post_setuid(), ->task_post_setuid() Removed in favour of security_task_fix_setuid(). (*) security_task_fix_setuid(), ->task_fix_setuid() Fix up the proposed new credentials for setuid(). This is used by cap_set_fix_setuid() to implicitly adjust capabilities in line with setuid() changes. Changes are made to the new credentials, rather than the task itself as in security_task_post_setuid(). (*) security_task_reparent_to_init(), ->task_reparent_to_init() Removed. Instead the task being reparented to init is referred directly to init's credentials. NOTE! This results in the loss of some state: SELinux's osid no longer records the sid of the thread that forked it. (*) security_key_alloc(), ->key_alloc() (*) security_key_permission(), ->key_permission() Changed. These now take cred pointers rather than task pointers to refer to the security context. (4) sys_capset(). This has been simplified and uses less locking. The LSM functions it calls have been merged. (5) reparent_to_kthreadd(). This gives the current thread the same credentials as init by simply using commit_thread() to point that way. (6) __sigqueue_alloc() and switch_uid() __sigqueue_alloc() can't stop the target task from changing its creds beneath it, so this function gets a reference to the currently applicable user_struct which it then passes into the sigqueue struct it returns if successful. switch_uid() is now called from commit_creds(), and possibly should be folded into that. commit_creds() should take care of protecting __sigqueue_alloc(). (7) [sg]et[ug]id() and co and [sg]et_current_groups. The set functions now all use prepare_creds(), commit_creds() and abort_creds() to build and check a new set of credentials before applying it. security_task_set[ug]id() is called inside the prepared section. This guarantees that nothing else will affect the creds until we've finished. The calling of set_dumpable() has been moved into commit_creds(). Much of the functionality of set_user() has been moved into commit_creds(). The get functions all simply access the data directly. (8) security_task_prctl() and cap_task_prctl(). security_task_prctl() has been modified to return -ENOSYS if it doesn't want to handle a function, or otherwise return the return value directly rather than through an argument. Additionally, cap_task_prctl() now prepares a new set of credentials, even if it doesn't end up using it. (9) Keyrings. A number of changes have been made to the keyrings code: (a) switch_uid_keyring(), copy_keys(), exit_keys() and suid_keys() have all been dropped and built in to the credentials functions directly. They may want separating out again later. (b) key_alloc() and search_process_keyrings() now take a cred pointer rather than a task pointer to specify the security context. (c) copy_creds() gives a new thread within the same thread group a new thread keyring if its parent had one, otherwise it discards the thread keyring. (d) The authorisation key now points directly to the credentials to extend the search into rather pointing to the task that carries them. (e) Installing thread, process or session keyrings causes a new set of credentials to be created, even though it's not strictly necessary for process or session keyrings (they're shared). (10) Usermode helper. The usermode helper code now carries a cred struct pointer in its subprocess_info struct instead of a new session keyring pointer. This set of credentials is derived from init_cred and installed on the new process after it has been cloned. call_usermodehelper_setup() allocates the new credentials and call_usermodehelper_freeinfo() discards them if they haven't been used. A special cred function (prepare_usermodeinfo_creds()) is provided specifically for call_usermodehelper_setup() to call. call_usermodehelper_setkeys() adjusts the credentials to sport the supplied keyring as the new session keyring. (11) SELinux. SELinux has a number of changes, in addition to those to support the LSM interface changes mentioned above: (a) selinux_setprocattr() no longer does its check for whether the current ptracer can access processes with the new SID inside the lock that covers getting the ptracer's SID. Whilst this lock ensures that the check is done with the ptracer pinned, the result is only valid until the lock is released, so there's no point doing it inside the lock. (12) is_single_threaded(). This function has been extracted from selinux_setprocattr() and put into a file of its own in the lib/ directory as join_session_keyring() now wants to use it too. The code in SELinux just checked to see whether a task shared mm_structs with other tasks (CLONE_VM), but that isn't good enough. We really want to know if they're part of the same thread group (CLONE_THREAD). (13) nfsd. The NFS server daemon now has to use the COW credentials to set the credentials it is going to use. It really needs to pass the credentials down to the functions it calls, but it can't do that until other patches in this series have been applied. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: James Morris <jmorris@namei.org> Signed-off-by: James Morris <jmorris@namei.org>
2008-11-14 02:39:23 +03:00
override_cred = prepare_creds();
if (!override_cred)
return NULL;
/*
* XXX access_need_override_creds performs checks in hopes of skipping
* this work. Make sure it stays in sync if making any changes in this
* routine.
*/
CRED: Inaugurate COW credentials Inaugurate copy-on-write credentials management. This uses RCU to manage the credentials pointer in the task_struct with respect to accesses by other tasks. A process may only modify its own credentials, and so does not need locking to access or modify its own credentials. A mutex (cred_replace_mutex) is added to the task_struct to control the effect of PTRACE_ATTACHED on credential calculations, particularly with respect to execve(). With this patch, the contents of an active credentials struct may not be changed directly; rather a new set of credentials must be prepared, modified and committed using something like the following sequence of events: struct cred *new = prepare_creds(); int ret = blah(new); if (ret < 0) { abort_creds(new); return ret; } return commit_creds(new); There are some exceptions to this rule: the keyrings pointed to by the active credentials may be instantiated - keyrings violate the COW rule as managing COW keyrings is tricky, given that it is possible for a task to directly alter the keys in a keyring in use by another task. To help enforce this, various pointers to sets of credentials, such as those in the task_struct, are declared const. The purpose of this is compile-time discouragement of altering credentials through those pointers. Once a set of credentials has been made public through one of these pointers, it may not be modified, except under special circumstances: (1) Its reference count may incremented and decremented. (2) The keyrings to which it points may be modified, but not replaced. The only safe way to modify anything else is to create a replacement and commit using the functions described in Documentation/credentials.txt (which will be added by a later patch). This patch and the preceding patches have been tested with the LTP SELinux testsuite. This patch makes several logical sets of alteration: (1) execve(). This now prepares and commits credentials in various places in the security code rather than altering the current creds directly. (2) Temporary credential overrides. do_coredump() and sys_faccessat() now prepare their own credentials and temporarily override the ones currently on the acting thread, whilst preventing interference from other threads by holding cred_replace_mutex on the thread being dumped. This will be replaced in a future patch by something that hands down the credentials directly to the functions being called, rather than altering the task's objective credentials. (3) LSM interface. A number of functions have been changed, added or removed: (*) security_capset_check(), ->capset_check() (*) security_capset_set(), ->capset_set() Removed in favour of security_capset(). (*) security_capset(), ->capset() New. This is passed a pointer to the new creds, a pointer to the old creds and the proposed capability sets. It should fill in the new creds or return an error. All pointers, barring the pointer to the new creds, are now const. (*) security_bprm_apply_creds(), ->bprm_apply_creds() Changed; now returns a value, which will cause the process to be killed if it's an error. (*) security_task_alloc(), ->task_alloc_security() Removed in favour of security_prepare_creds(). (*) security_cred_free(), ->cred_free() New. Free security data attached to cred->security. (*) security_prepare_creds(), ->cred_prepare() New. Duplicate any security data attached to cred->security. (*) security_commit_creds(), ->cred_commit() New. Apply any security effects for the upcoming installation of new security by commit_creds(). (*) security_task_post_setuid(), ->task_post_setuid() Removed in favour of security_task_fix_setuid(). (*) security_task_fix_setuid(), ->task_fix_setuid() Fix up the proposed new credentials for setuid(). This is used by cap_set_fix_setuid() to implicitly adjust capabilities in line with setuid() changes. Changes are made to the new credentials, rather than the task itself as in security_task_post_setuid(). (*) security_task_reparent_to_init(), ->task_reparent_to_init() Removed. Instead the task being reparented to init is referred directly to init's credentials. NOTE! This results in the loss of some state: SELinux's osid no longer records the sid of the thread that forked it. (*) security_key_alloc(), ->key_alloc() (*) security_key_permission(), ->key_permission() Changed. These now take cred pointers rather than task pointers to refer to the security context. (4) sys_capset(). This has been simplified and uses less locking. The LSM functions it calls have been merged. (5) reparent_to_kthreadd(). This gives the current thread the same credentials as init by simply using commit_thread() to point that way. (6) __sigqueue_alloc() and switch_uid() __sigqueue_alloc() can't stop the target task from changing its creds beneath it, so this function gets a reference to the currently applicable user_struct which it then passes into the sigqueue struct it returns if successful. switch_uid() is now called from commit_creds(), and possibly should be folded into that. commit_creds() should take care of protecting __sigqueue_alloc(). (7) [sg]et[ug]id() and co and [sg]et_current_groups. The set functions now all use prepare_creds(), commit_creds() and abort_creds() to build and check a new set of credentials before applying it. security_task_set[ug]id() is called inside the prepared section. This guarantees that nothing else will affect the creds until we've finished. The calling of set_dumpable() has been moved into commit_creds(). Much of the functionality of set_user() has been moved into commit_creds(). The get functions all simply access the data directly. (8) security_task_prctl() and cap_task_prctl(). security_task_prctl() has been modified to return -ENOSYS if it doesn't want to handle a function, or otherwise return the return value directly rather than through an argument. Additionally, cap_task_prctl() now prepares a new set of credentials, even if it doesn't end up using it. (9) Keyrings. A number of changes have been made to the keyrings code: (a) switch_uid_keyring(), copy_keys(), exit_keys() and suid_keys() have all been dropped and built in to the credentials functions directly. They may want separating out again later. (b) key_alloc() and search_process_keyrings() now take a cred pointer rather than a task pointer to specify the security context. (c) copy_creds() gives a new thread within the same thread group a new thread keyring if its parent had one, otherwise it discards the thread keyring. (d) The authorisation key now points directly to the credentials to extend the search into rather pointing to the task that carries them. (e) Installing thread, process or session keyrings causes a new set of credentials to be created, even though it's not strictly necessary for process or session keyrings (they're shared). (10) Usermode helper. The usermode helper code now carries a cred struct pointer in its subprocess_info struct instead of a new session keyring pointer. This set of credentials is derived from init_cred and installed on the new process after it has been cloned. call_usermodehelper_setup() allocates the new credentials and call_usermodehelper_freeinfo() discards them if they haven't been used. A special cred function (prepare_usermodeinfo_creds()) is provided specifically for call_usermodehelper_setup() to call. call_usermodehelper_setkeys() adjusts the credentials to sport the supplied keyring as the new session keyring. (11) SELinux. SELinux has a number of changes, in addition to those to support the LSM interface changes mentioned above: (a) selinux_setprocattr() no longer does its check for whether the current ptracer can access processes with the new SID inside the lock that covers getting the ptracer's SID. Whilst this lock ensures that the check is done with the ptracer pinned, the result is only valid until the lock is released, so there's no point doing it inside the lock. (12) is_single_threaded(). This function has been extracted from selinux_setprocattr() and put into a file of its own in the lib/ directory as join_session_keyring() now wants to use it too. The code in SELinux just checked to see whether a task shared mm_structs with other tasks (CLONE_VM), but that isn't good enough. We really want to know if they're part of the same thread group (CLONE_THREAD). (13) nfsd. The NFS server daemon now has to use the COW credentials to set the credentials it is going to use. It really needs to pass the credentials down to the functions it calls, but it can't do that until other patches in this series have been applied. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: James Morris <jmorris@namei.org> Signed-off-by: James Morris <jmorris@namei.org>
2008-11-14 02:39:23 +03:00
override_cred->fsuid = override_cred->uid;
override_cred->fsgid = override_cred->gid;
if (!issecure(SECURE_NO_SETUID_FIXUP)) {
/* Clear the capabilities if we switch to a non-root user */
kuid_t root_uid = make_kuid(override_cred->user_ns, 0);
if (!uid_eq(override_cred->uid, root_uid))
CRED: Inaugurate COW credentials Inaugurate copy-on-write credentials management. This uses RCU to manage the credentials pointer in the task_struct with respect to accesses by other tasks. A process may only modify its own credentials, and so does not need locking to access or modify its own credentials. A mutex (cred_replace_mutex) is added to the task_struct to control the effect of PTRACE_ATTACHED on credential calculations, particularly with respect to execve(). With this patch, the contents of an active credentials struct may not be changed directly; rather a new set of credentials must be prepared, modified and committed using something like the following sequence of events: struct cred *new = prepare_creds(); int ret = blah(new); if (ret < 0) { abort_creds(new); return ret; } return commit_creds(new); There are some exceptions to this rule: the keyrings pointed to by the active credentials may be instantiated - keyrings violate the COW rule as managing COW keyrings is tricky, given that it is possible for a task to directly alter the keys in a keyring in use by another task. To help enforce this, various pointers to sets of credentials, such as those in the task_struct, are declared const. The purpose of this is compile-time discouragement of altering credentials through those pointers. Once a set of credentials has been made public through one of these pointers, it may not be modified, except under special circumstances: (1) Its reference count may incremented and decremented. (2) The keyrings to which it points may be modified, but not replaced. The only safe way to modify anything else is to create a replacement and commit using the functions described in Documentation/credentials.txt (which will be added by a later patch). This patch and the preceding patches have been tested with the LTP SELinux testsuite. This patch makes several logical sets of alteration: (1) execve(). This now prepares and commits credentials in various places in the security code rather than altering the current creds directly. (2) Temporary credential overrides. do_coredump() and sys_faccessat() now prepare their own credentials and temporarily override the ones currently on the acting thread, whilst preventing interference from other threads by holding cred_replace_mutex on the thread being dumped. This will be replaced in a future patch by something that hands down the credentials directly to the functions being called, rather than altering the task's objective credentials. (3) LSM interface. A number of functions have been changed, added or removed: (*) security_capset_check(), ->capset_check() (*) security_capset_set(), ->capset_set() Removed in favour of security_capset(). (*) security_capset(), ->capset() New. This is passed a pointer to the new creds, a pointer to the old creds and the proposed capability sets. It should fill in the new creds or return an error. All pointers, barring the pointer to the new creds, are now const. (*) security_bprm_apply_creds(), ->bprm_apply_creds() Changed; now returns a value, which will cause the process to be killed if it's an error. (*) security_task_alloc(), ->task_alloc_security() Removed in favour of security_prepare_creds(). (*) security_cred_free(), ->cred_free() New. Free security data attached to cred->security. (*) security_prepare_creds(), ->cred_prepare() New. Duplicate any security data attached to cred->security. (*) security_commit_creds(), ->cred_commit() New. Apply any security effects for the upcoming installation of new security by commit_creds(). (*) security_task_post_setuid(), ->task_post_setuid() Removed in favour of security_task_fix_setuid(). (*) security_task_fix_setuid(), ->task_fix_setuid() Fix up the proposed new credentials for setuid(). This is used by cap_set_fix_setuid() to implicitly adjust capabilities in line with setuid() changes. Changes are made to the new credentials, rather than the task itself as in security_task_post_setuid(). (*) security_task_reparent_to_init(), ->task_reparent_to_init() Removed. Instead the task being reparented to init is referred directly to init's credentials. NOTE! This results in the loss of some state: SELinux's osid no longer records the sid of the thread that forked it. (*) security_key_alloc(), ->key_alloc() (*) security_key_permission(), ->key_permission() Changed. These now take cred pointers rather than task pointers to refer to the security context. (4) sys_capset(). This has been simplified and uses less locking. The LSM functions it calls have been merged. (5) reparent_to_kthreadd(). This gives the current thread the same credentials as init by simply using commit_thread() to point that way. (6) __sigqueue_alloc() and switch_uid() __sigqueue_alloc() can't stop the target task from changing its creds beneath it, so this function gets a reference to the currently applicable user_struct which it then passes into the sigqueue struct it returns if successful. switch_uid() is now called from commit_creds(), and possibly should be folded into that. commit_creds() should take care of protecting __sigqueue_alloc(). (7) [sg]et[ug]id() and co and [sg]et_current_groups. The set functions now all use prepare_creds(), commit_creds() and abort_creds() to build and check a new set of credentials before applying it. security_task_set[ug]id() is called inside the prepared section. This guarantees that nothing else will affect the creds until we've finished. The calling of set_dumpable() has been moved into commit_creds(). Much of the functionality of set_user() has been moved into commit_creds(). The get functions all simply access the data directly. (8) security_task_prctl() and cap_task_prctl(). security_task_prctl() has been modified to return -ENOSYS if it doesn't want to handle a function, or otherwise return the return value directly rather than through an argument. Additionally, cap_task_prctl() now prepares a new set of credentials, even if it doesn't end up using it. (9) Keyrings. A number of changes have been made to the keyrings code: (a) switch_uid_keyring(), copy_keys(), exit_keys() and suid_keys() have all been dropped and built in to the credentials functions directly. They may want separating out again later. (b) key_alloc() and search_process_keyrings() now take a cred pointer rather than a task pointer to specify the security context. (c) copy_creds() gives a new thread within the same thread group a new thread keyring if its parent had one, otherwise it discards the thread keyring. (d) The authorisation key now points directly to the credentials to extend the search into rather pointing to the task that carries them. (e) Installing thread, process or session keyrings causes a new set of credentials to be created, even though it's not strictly necessary for process or session keyrings (they're shared). (10) Usermode helper. The usermode helper code now carries a cred struct pointer in its subprocess_info struct instead of a new session keyring pointer. This set of credentials is derived from init_cred and installed on the new process after it has been cloned. call_usermodehelper_setup() allocates the new credentials and call_usermodehelper_freeinfo() discards them if they haven't been used. A special cred function (prepare_usermodeinfo_creds()) is provided specifically for call_usermodehelper_setup() to call. call_usermodehelper_setkeys() adjusts the credentials to sport the supplied keyring as the new session keyring. (11) SELinux. SELinux has a number of changes, in addition to those to support the LSM interface changes mentioned above: (a) selinux_setprocattr() no longer does its check for whether the current ptracer can access processes with the new SID inside the lock that covers getting the ptracer's SID. Whilst this lock ensures that the check is done with the ptracer pinned, the result is only valid until the lock is released, so there's no point doing it inside the lock. (12) is_single_threaded(). This function has been extracted from selinux_setprocattr() and put into a file of its own in the lib/ directory as join_session_keyring() now wants to use it too. The code in SELinux just checked to see whether a task shared mm_structs with other tasks (CLONE_VM), but that isn't good enough. We really want to know if they're part of the same thread group (CLONE_THREAD). (13) nfsd. The NFS server daemon now has to use the COW credentials to set the credentials it is going to use. It really needs to pass the credentials down to the functions it calls, but it can't do that until other patches in this series have been applied. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: James Morris <jmorris@namei.org> Signed-off-by: James Morris <jmorris@namei.org>
2008-11-14 02:39:23 +03:00
cap_clear(override_cred->cap_effective);
else
CRED: Inaugurate COW credentials Inaugurate copy-on-write credentials management. This uses RCU to manage the credentials pointer in the task_struct with respect to accesses by other tasks. A process may only modify its own credentials, and so does not need locking to access or modify its own credentials. A mutex (cred_replace_mutex) is added to the task_struct to control the effect of PTRACE_ATTACHED on credential calculations, particularly with respect to execve(). With this patch, the contents of an active credentials struct may not be changed directly; rather a new set of credentials must be prepared, modified and committed using something like the following sequence of events: struct cred *new = prepare_creds(); int ret = blah(new); if (ret < 0) { abort_creds(new); return ret; } return commit_creds(new); There are some exceptions to this rule: the keyrings pointed to by the active credentials may be instantiated - keyrings violate the COW rule as managing COW keyrings is tricky, given that it is possible for a task to directly alter the keys in a keyring in use by another task. To help enforce this, various pointers to sets of credentials, such as those in the task_struct, are declared const. The purpose of this is compile-time discouragement of altering credentials through those pointers. Once a set of credentials has been made public through one of these pointers, it may not be modified, except under special circumstances: (1) Its reference count may incremented and decremented. (2) The keyrings to which it points may be modified, but not replaced. The only safe way to modify anything else is to create a replacement and commit using the functions described in Documentation/credentials.txt (which will be added by a later patch). This patch and the preceding patches have been tested with the LTP SELinux testsuite. This patch makes several logical sets of alteration: (1) execve(). This now prepares and commits credentials in various places in the security code rather than altering the current creds directly. (2) Temporary credential overrides. do_coredump() and sys_faccessat() now prepare their own credentials and temporarily override the ones currently on the acting thread, whilst preventing interference from other threads by holding cred_replace_mutex on the thread being dumped. This will be replaced in a future patch by something that hands down the credentials directly to the functions being called, rather than altering the task's objective credentials. (3) LSM interface. A number of functions have been changed, added or removed: (*) security_capset_check(), ->capset_check() (*) security_capset_set(), ->capset_set() Removed in favour of security_capset(). (*) security_capset(), ->capset() New. This is passed a pointer to the new creds, a pointer to the old creds and the proposed capability sets. It should fill in the new creds or return an error. All pointers, barring the pointer to the new creds, are now const. (*) security_bprm_apply_creds(), ->bprm_apply_creds() Changed; now returns a value, which will cause the process to be killed if it's an error. (*) security_task_alloc(), ->task_alloc_security() Removed in favour of security_prepare_creds(). (*) security_cred_free(), ->cred_free() New. Free security data attached to cred->security. (*) security_prepare_creds(), ->cred_prepare() New. Duplicate any security data attached to cred->security. (*) security_commit_creds(), ->cred_commit() New. Apply any security effects for the upcoming installation of new security by commit_creds(). (*) security_task_post_setuid(), ->task_post_setuid() Removed in favour of security_task_fix_setuid(). (*) security_task_fix_setuid(), ->task_fix_setuid() Fix up the proposed new credentials for setuid(). This is used by cap_set_fix_setuid() to implicitly adjust capabilities in line with setuid() changes. Changes are made to the new credentials, rather than the task itself as in security_task_post_setuid(). (*) security_task_reparent_to_init(), ->task_reparent_to_init() Removed. Instead the task being reparented to init is referred directly to init's credentials. NOTE! This results in the loss of some state: SELinux's osid no longer records the sid of the thread that forked it. (*) security_key_alloc(), ->key_alloc() (*) security_key_permission(), ->key_permission() Changed. These now take cred pointers rather than task pointers to refer to the security context. (4) sys_capset(). This has been simplified and uses less locking. The LSM functions it calls have been merged. (5) reparent_to_kthreadd(). This gives the current thread the same credentials as init by simply using commit_thread() to point that way. (6) __sigqueue_alloc() and switch_uid() __sigqueue_alloc() can't stop the target task from changing its creds beneath it, so this function gets a reference to the currently applicable user_struct which it then passes into the sigqueue struct it returns if successful. switch_uid() is now called from commit_creds(), and possibly should be folded into that. commit_creds() should take care of protecting __sigqueue_alloc(). (7) [sg]et[ug]id() and co and [sg]et_current_groups. The set functions now all use prepare_creds(), commit_creds() and abort_creds() to build and check a new set of credentials before applying it. security_task_set[ug]id() is called inside the prepared section. This guarantees that nothing else will affect the creds until we've finished. The calling of set_dumpable() has been moved into commit_creds(). Much of the functionality of set_user() has been moved into commit_creds(). The get functions all simply access the data directly. (8) security_task_prctl() and cap_task_prctl(). security_task_prctl() has been modified to return -ENOSYS if it doesn't want to handle a function, or otherwise return the return value directly rather than through an argument. Additionally, cap_task_prctl() now prepares a new set of credentials, even if it doesn't end up using it. (9) Keyrings. A number of changes have been made to the keyrings code: (a) switch_uid_keyring(), copy_keys(), exit_keys() and suid_keys() have all been dropped and built in to the credentials functions directly. They may want separating out again later. (b) key_alloc() and search_process_keyrings() now take a cred pointer rather than a task pointer to specify the security context. (c) copy_creds() gives a new thread within the same thread group a new thread keyring if its parent had one, otherwise it discards the thread keyring. (d) The authorisation key now points directly to the credentials to extend the search into rather pointing to the task that carries them. (e) Installing thread, process or session keyrings causes a new set of credentials to be created, even though it's not strictly necessary for process or session keyrings (they're shared). (10) Usermode helper. The usermode helper code now carries a cred struct pointer in its subprocess_info struct instead of a new session keyring pointer. This set of credentials is derived from init_cred and installed on the new process after it has been cloned. call_usermodehelper_setup() allocates the new credentials and call_usermodehelper_freeinfo() discards them if they haven't been used. A special cred function (prepare_usermodeinfo_creds()) is provided specifically for call_usermodehelper_setup() to call. call_usermodehelper_setkeys() adjusts the credentials to sport the supplied keyring as the new session keyring. (11) SELinux. SELinux has a number of changes, in addition to those to support the LSM interface changes mentioned above: (a) selinux_setprocattr() no longer does its check for whether the current ptracer can access processes with the new SID inside the lock that covers getting the ptracer's SID. Whilst this lock ensures that the check is done with the ptracer pinned, the result is only valid until the lock is released, so there's no point doing it inside the lock. (12) is_single_threaded(). This function has been extracted from selinux_setprocattr() and put into a file of its own in the lib/ directory as join_session_keyring() now wants to use it too. The code in SELinux just checked to see whether a task shared mm_structs with other tasks (CLONE_VM), but that isn't good enough. We really want to know if they're part of the same thread group (CLONE_THREAD). (13) nfsd. The NFS server daemon now has to use the COW credentials to set the credentials it is going to use. It really needs to pass the credentials down to the functions it calls, but it can't do that until other patches in this series have been applied. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: James Morris <jmorris@namei.org> Signed-off-by: James Morris <jmorris@namei.org>
2008-11-14 02:39:23 +03:00
override_cred->cap_effective =
override_cred->cap_permitted;
}
access: avoid the RCU grace period for the temporary subjective credentials It turns out that 'access()' (and 'faccessat()') can cause a lot of RCU work because it installs a temporary credential that gets allocated and freed for each system call. The allocation and freeing overhead is mostly benign, but because credentials can be accessed under the RCU read lock, the freeing involves a RCU grace period. Which is not a huge deal normally, but if you have a lot of access() calls, this causes a fair amount of seconday damage: instead of having a nice alloc/free patterns that hits in hot per-CPU slab caches, you have all those delayed free's, and on big machines with hundreds of cores, the RCU overhead can end up being enormous. But it turns out that all of this is entirely unnecessary. Exactly because access() only installs the credential as the thread-local subjective credential, the temporary cred pointer doesn't actually need to be RCU free'd at all. Once we're done using it, we can just free it synchronously and avoid all the RCU overhead. So add a 'non_rcu' flag to 'struct cred', which can be set by users that know they only use it in non-RCU context (there are other potential users for this). We can make it a union with the rcu freeing list head that we need for the RCU case, so this doesn't need any extra storage. Note that this also makes 'get_current_cred()' clear the new non_rcu flag, in case we have filesystems that take a long-term reference to the cred and then expect the RCU delayed freeing afterwards. It's not entirely clear that this is required, but it makes for clear semantics: the subjective cred remains non-RCU as long as you only access it synchronously using the thread-local accessors, but you _can_ use it as a generic cred if you want to. It is possible that we should just remove the whole RCU markings for ->cred entirely. Only ->real_cred is really supposed to be accessed through RCU, and the long-term cred copies that nfs uses might want to explicitly re-enable RCU freeing if required, rather than have get_current_cred() do it implicitly. But this is a "minimal semantic changes" change for the immediate problem. Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Eric Dumazet <edumazet@google.com> Acked-by: Paul E. McKenney <paulmck@linux.ibm.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Jan Glauber <jglauber@marvell.com> Cc: Jiri Kosina <jikos@kernel.org> Cc: Jayachandran Chandrasekharan Nair <jnair@marvell.com> Cc: Greg KH <greg@kroah.com> Cc: Kees Cook <keescook@chromium.org> Cc: David Howells <dhowells@redhat.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-07-11 19:54:40 +03:00
/*
* The new set of credentials can *only* be used in
* task-synchronous circumstances, and does not need
* RCU freeing, unless somebody then takes a separate
* reference to it.
*
* NOTE! This is _only_ true because this credential
* is used purely for override_creds() that installs
* it as the subjective cred. Other threads will be
* accessing ->real_cred, not the subjective cred.
*
* If somebody _does_ make a copy of this (using the
* 'get_current_cred()' function), that will clear the
* non_rcu field, because now that other user may be
* expecting RCU freeing. But normal thread-synchronous
* cred accesses will keep things non-RCY.
*/
override_cred->non_rcu = 1;
CRED: Inaugurate COW credentials Inaugurate copy-on-write credentials management. This uses RCU to manage the credentials pointer in the task_struct with respect to accesses by other tasks. A process may only modify its own credentials, and so does not need locking to access or modify its own credentials. A mutex (cred_replace_mutex) is added to the task_struct to control the effect of PTRACE_ATTACHED on credential calculations, particularly with respect to execve(). With this patch, the contents of an active credentials struct may not be changed directly; rather a new set of credentials must be prepared, modified and committed using something like the following sequence of events: struct cred *new = prepare_creds(); int ret = blah(new); if (ret < 0) { abort_creds(new); return ret; } return commit_creds(new); There are some exceptions to this rule: the keyrings pointed to by the active credentials may be instantiated - keyrings violate the COW rule as managing COW keyrings is tricky, given that it is possible for a task to directly alter the keys in a keyring in use by another task. To help enforce this, various pointers to sets of credentials, such as those in the task_struct, are declared const. The purpose of this is compile-time discouragement of altering credentials through those pointers. Once a set of credentials has been made public through one of these pointers, it may not be modified, except under special circumstances: (1) Its reference count may incremented and decremented. (2) The keyrings to which it points may be modified, but not replaced. The only safe way to modify anything else is to create a replacement and commit using the functions described in Documentation/credentials.txt (which will be added by a later patch). This patch and the preceding patches have been tested with the LTP SELinux testsuite. This patch makes several logical sets of alteration: (1) execve(). This now prepares and commits credentials in various places in the security code rather than altering the current creds directly. (2) Temporary credential overrides. do_coredump() and sys_faccessat() now prepare their own credentials and temporarily override the ones currently on the acting thread, whilst preventing interference from other threads by holding cred_replace_mutex on the thread being dumped. This will be replaced in a future patch by something that hands down the credentials directly to the functions being called, rather than altering the task's objective credentials. (3) LSM interface. A number of functions have been changed, added or removed: (*) security_capset_check(), ->capset_check() (*) security_capset_set(), ->capset_set() Removed in favour of security_capset(). (*) security_capset(), ->capset() New. This is passed a pointer to the new creds, a pointer to the old creds and the proposed capability sets. It should fill in the new creds or return an error. All pointers, barring the pointer to the new creds, are now const. (*) security_bprm_apply_creds(), ->bprm_apply_creds() Changed; now returns a value, which will cause the process to be killed if it's an error. (*) security_task_alloc(), ->task_alloc_security() Removed in favour of security_prepare_creds(). (*) security_cred_free(), ->cred_free() New. Free security data attached to cred->security. (*) security_prepare_creds(), ->cred_prepare() New. Duplicate any security data attached to cred->security. (*) security_commit_creds(), ->cred_commit() New. Apply any security effects for the upcoming installation of new security by commit_creds(). (*) security_task_post_setuid(), ->task_post_setuid() Removed in favour of security_task_fix_setuid(). (*) security_task_fix_setuid(), ->task_fix_setuid() Fix up the proposed new credentials for setuid(). This is used by cap_set_fix_setuid() to implicitly adjust capabilities in line with setuid() changes. Changes are made to the new credentials, rather than the task itself as in security_task_post_setuid(). (*) security_task_reparent_to_init(), ->task_reparent_to_init() Removed. Instead the task being reparented to init is referred directly to init's credentials. NOTE! This results in the loss of some state: SELinux's osid no longer records the sid of the thread that forked it. (*) security_key_alloc(), ->key_alloc() (*) security_key_permission(), ->key_permission() Changed. These now take cred pointers rather than task pointers to refer to the security context. (4) sys_capset(). This has been simplified and uses less locking. The LSM functions it calls have been merged. (5) reparent_to_kthreadd(). This gives the current thread the same credentials as init by simply using commit_thread() to point that way. (6) __sigqueue_alloc() and switch_uid() __sigqueue_alloc() can't stop the target task from changing its creds beneath it, so this function gets a reference to the currently applicable user_struct which it then passes into the sigqueue struct it returns if successful. switch_uid() is now called from commit_creds(), and possibly should be folded into that. commit_creds() should take care of protecting __sigqueue_alloc(). (7) [sg]et[ug]id() and co and [sg]et_current_groups. The set functions now all use prepare_creds(), commit_creds() and abort_creds() to build and check a new set of credentials before applying it. security_task_set[ug]id() is called inside the prepared section. This guarantees that nothing else will affect the creds until we've finished. The calling of set_dumpable() has been moved into commit_creds(). Much of the functionality of set_user() has been moved into commit_creds(). The get functions all simply access the data directly. (8) security_task_prctl() and cap_task_prctl(). security_task_prctl() has been modified to return -ENOSYS if it doesn't want to handle a function, or otherwise return the return value directly rather than through an argument. Additionally, cap_task_prctl() now prepares a new set of credentials, even if it doesn't end up using it. (9) Keyrings. A number of changes have been made to the keyrings code: (a) switch_uid_keyring(), copy_keys(), exit_keys() and suid_keys() have all been dropped and built in to the credentials functions directly. They may want separating out again later. (b) key_alloc() and search_process_keyrings() now take a cred pointer rather than a task pointer to specify the security context. (c) copy_creds() gives a new thread within the same thread group a new thread keyring if its parent had one, otherwise it discards the thread keyring. (d) The authorisation key now points directly to the credentials to extend the search into rather pointing to the task that carries them. (e) Installing thread, process or session keyrings causes a new set of credentials to be created, even though it's not strictly necessary for process or session keyrings (they're shared). (10) Usermode helper. The usermode helper code now carries a cred struct pointer in its subprocess_info struct instead of a new session keyring pointer. This set of credentials is derived from init_cred and installed on the new process after it has been cloned. call_usermodehelper_setup() allocates the new credentials and call_usermodehelper_freeinfo() discards them if they haven't been used. A special cred function (prepare_usermodeinfo_creds()) is provided specifically for call_usermodehelper_setup() to call. call_usermodehelper_setkeys() adjusts the credentials to sport the supplied keyring as the new session keyring. (11) SELinux. SELinux has a number of changes, in addition to those to support the LSM interface changes mentioned above: (a) selinux_setprocattr() no longer does its check for whether the current ptracer can access processes with the new SID inside the lock that covers getting the ptracer's SID. Whilst this lock ensures that the check is done with the ptracer pinned, the result is only valid until the lock is released, so there's no point doing it inside the lock. (12) is_single_threaded(). This function has been extracted from selinux_setprocattr() and put into a file of its own in the lib/ directory as join_session_keyring() now wants to use it too. The code in SELinux just checked to see whether a task shared mm_structs with other tasks (CLONE_VM), but that isn't good enough. We really want to know if they're part of the same thread group (CLONE_THREAD). (13) nfsd. The NFS server daemon now has to use the COW credentials to set the credentials it is going to use. It really needs to pass the credentials down to the functions it calls, but it can't do that until other patches in this series have been applied. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: James Morris <jmorris@namei.org> Signed-off-by: James Morris <jmorris@namei.org>
2008-11-14 02:39:23 +03:00
old_cred = override_creds(override_cred);
/* override_cred() gets its own ref */
put_cred(override_cred);
return old_cred;
}
static long do_faccessat(int dfd, const char __user *filename, int mode, int flags)
{
struct path path;
struct inode *inode;
int res;
unsigned int lookup_flags = LOOKUP_FOLLOW;
const struct cred *old_cred = NULL;
if (mode & ~S_IRWXO) /* where's F_OK, X_OK, W_OK, R_OK? */
return -EINVAL;
if (flags & ~(AT_EACCESS | AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH))
return -EINVAL;
if (flags & AT_SYMLINK_NOFOLLOW)
lookup_flags &= ~LOOKUP_FOLLOW;
if (flags & AT_EMPTY_PATH)
lookup_flags |= LOOKUP_EMPTY;
if (access_need_override_creds(flags)) {
old_cred = access_override_creds();
if (!old_cred)
return -ENOMEM;
}
retry:
res = user_path_at(dfd, filename, lookup_flags, &path);
if (res)
goto out;
inode = d_backing_inode(path.dentry);
if ((mode & MAY_EXEC) && S_ISREG(inode->i_mode)) {
/*
* MAY_EXEC on regular files is denied if the fs is mounted
* with the "noexec" flag.
*/
res = -EACCES;
vfs: Commit to never having exectuables on proc and sysfs. Today proc and sysfs do not contain any executable files. Several applications today mount proc or sysfs without noexec and nosuid and then depend on there being no exectuables files on proc or sysfs. Having any executable files show on proc or sysfs would cause a user space visible regression, and most likely security problems. Therefore commit to never allowing executables on proc and sysfs by adding a new flag to mark them as filesystems without executables and enforce that flag. Test the flag where MNT_NOEXEC is tested today, so that the only user visible effect will be that exectuables will be treated as if the execute bit is cleared. The filesystems proc and sysfs do not currently incoporate any executable files so this does not result in any user visible effects. This makes it unnecessary to vet changes to proc and sysfs tightly for adding exectuable files or changes to chattr that would modify existing files, as no matter what the individual file say they will not be treated as exectuable files by the vfs. Not having to vet changes to closely is important as without this we are only one proc_create call (or another goof up in the implementation of notify_change) from having problematic executables on proc. Those mistakes are all too easy to make and would create a situation where there are security issues or the assumptions of some program having to be broken (and cause userspace regressions). Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2015-06-29 22:42:03 +03:00
if (path_noexec(&path))
goto out_path_release;
}
res = inode_permission(mnt_idmap(path.mnt), inode, mode | MAY_ACCESS);
/* SuS v2 requires we report a read only fs too */
if (res || !(mode & S_IWOTH) || special_file(inode->i_mode))
goto out_path_release;
/*
* This is a rare case where using __mnt_is_readonly()
* is OK without a mnt_want/drop_write() pair. Since
* no actual write to the fs is performed here, we do
* not need to telegraph to that to anyone.
*
* By doing this, we accept that this access is
* inherently racy and know that the fs may change
* state before we even see this result.
*/
if (__mnt_is_readonly(path.mnt))
res = -EROFS;
out_path_release:
path_put(&path);
if (retry_estale(res, lookup_flags)) {
lookup_flags |= LOOKUP_REVAL;
goto retry;
}
out:
if (old_cred)
revert_creds(old_cred);
return res;
}
SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
{
return do_faccessat(dfd, filename, mode, 0);
}
SYSCALL_DEFINE4(faccessat2, int, dfd, const char __user *, filename, int, mode,
int, flags)
{
return do_faccessat(dfd, filename, mode, flags);
}
SYSCALL_DEFINE2(access, const char __user *, filename, int, mode)
[PATCH] vfs: *at functions: core Here is a series of patches which introduce in total 13 new system calls which take a file descriptor/filename pair instead of a single file name. These functions, openat etc, have been discussed on numerous occasions. They are needed to implement race-free filesystem traversal, they are necessary to implement a virtual per-thread current working directory (think multi-threaded backup software), etc. We have in glibc today implementations of the interfaces which use the /proc/self/fd magic. But this code is rather expensive. Here are some results (similar to what Jim Meyering posted before). The test creates a deep directory hierarchy on a tmpfs filesystem. Then rm -fr is used to remove all directories. Without syscall support I get this: real 0m31.921s user 0m0.688s sys 0m31.234s With syscall support the results are much better: real 0m20.699s user 0m0.536s sys 0m20.149s The interfaces are for obvious reasons currently not much used. But they'll be used. coreutils (and Jeff's posixutils) are already using them. Furthermore, code like ftw/fts in libc (maybe even glob) will also start using them. I expect a patch to make follow soon. Every program which is walking the filesystem tree will benefit. Signed-off-by: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@ftp.linux.org.uk> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-19 04:43:53 +03:00
{
return do_faccessat(AT_FDCWD, filename, mode, 0);
[PATCH] vfs: *at functions: core Here is a series of patches which introduce in total 13 new system calls which take a file descriptor/filename pair instead of a single file name. These functions, openat etc, have been discussed on numerous occasions. They are needed to implement race-free filesystem traversal, they are necessary to implement a virtual per-thread current working directory (think multi-threaded backup software), etc. We have in glibc today implementations of the interfaces which use the /proc/self/fd magic. But this code is rather expensive. Here are some results (similar to what Jim Meyering posted before). The test creates a deep directory hierarchy on a tmpfs filesystem. Then rm -fr is used to remove all directories. Without syscall support I get this: real 0m31.921s user 0m0.688s sys 0m31.234s With syscall support the results are much better: real 0m20.699s user 0m0.536s sys 0m20.149s The interfaces are for obvious reasons currently not much used. But they'll be used. coreutils (and Jeff's posixutils) are already using them. Furthermore, code like ftw/fts in libc (maybe even glob) will also start using them. I expect a patch to make follow soon. Every program which is walking the filesystem tree will benefit. Signed-off-by: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@ftp.linux.org.uk> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-19 04:43:53 +03:00
}
SYSCALL_DEFINE1(chdir, const char __user *, filename)
{
struct path path;
int error;
unsigned int lookup_flags = LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
retry:
error = user_path_at(AT_FDCWD, filename, lookup_flags, &path);
if (error)
goto out;
error = path_permission(&path, MAY_EXEC | MAY_CHDIR);
if (error)
goto dput_and_out;
set_fs_pwd(current->fs, &path);
dput_and_out:
path_put(&path);
if (retry_estale(error, lookup_flags)) {
lookup_flags |= LOOKUP_REVAL;
goto retry;
}
out:
return error;
}
SYSCALL_DEFINE1(fchdir, unsigned int, fd)
{
struct fd f = fdget_raw(fd);
int error;
error = -EBADF;
if (!f.file)
goto out;
error = -ENOTDIR;
if (!d_can_lookup(f.file->f_path.dentry))
goto out_putf;
error = file_permission(f.file, MAY_EXEC | MAY_CHDIR);
if (!error)
set_fs_pwd(current->fs, &f.file->f_path);
out_putf:
fdput(f);
out:
return error;
}
SYSCALL_DEFINE1(chroot, const char __user *, filename)
{
struct path path;
int error;
unsigned int lookup_flags = LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
retry:
error = user_path_at(AT_FDCWD, filename, lookup_flags, &path);
if (error)
goto out;
error = path_permission(&path, MAY_EXEC | MAY_CHDIR);
if (error)
goto dput_and_out;
error = -EPERM;
if (!ns_capable(current_user_ns(), CAP_SYS_CHROOT))
goto dput_and_out;
error = security_path_chroot(&path);
if (error)
goto dput_and_out;
set_fs_root(current->fs, &path);
error = 0;
dput_and_out:
path_put(&path);
if (retry_estale(error, lookup_flags)) {
lookup_flags |= LOOKUP_REVAL;
goto retry;
}
out:
return error;
}
int chmod_common(const struct path *path, umode_t mode)
{
struct inode *inode = path->dentry->d_inode;
struct inode *delegated_inode = NULL;
struct iattr newattrs;
int error;
error = mnt_want_write(path->mnt);
if (error)
return error;
retry_deleg:
inode_lock(inode);
error = security_path_chmod(path, mode);
if (error)
goto out_unlock;
newattrs.ia_mode = (mode & S_IALLUGO) | (inode->i_mode & ~S_IALLUGO);
newattrs.ia_valid = ATTR_MODE | ATTR_CTIME;
error = notify_change(mnt_idmap(path->mnt), path->dentry,
&newattrs, &delegated_inode);
out_unlock:
inode_unlock(inode);
if (delegated_inode) {
error = break_deleg_wait(&delegated_inode);
if (!error)
goto retry_deleg;
}
mnt_drop_write(path->mnt);
return error;
}
int vfs_fchmod(struct file *file, umode_t mode)
{
audit_file(file);
return chmod_common(&file->f_path, mode);
}
SYSCALL_DEFINE2(fchmod, unsigned int, fd, umode_t, mode)
{
struct fd f = fdget(fd);
int err = -EBADF;
if (f.file) {
err = vfs_fchmod(f.file, mode);
fdput(f);
}
return err;
}
static int do_fchmodat(int dfd, const char __user *filename, umode_t mode,
unsigned int flags)
{
struct path path;
int error;
unsigned int lookup_flags;
if (unlikely(flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)))
return -EINVAL;
lookup_flags = (flags & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
if (flags & AT_EMPTY_PATH)
lookup_flags |= LOOKUP_EMPTY;
retry:
error = user_path_at(dfd, filename, lookup_flags, &path);
if (!error) {
error = chmod_common(&path, mode);
path_put(&path);
if (retry_estale(error, lookup_flags)) {
lookup_flags |= LOOKUP_REVAL;
goto retry;
}
}
return error;
}
SYSCALL_DEFINE4(fchmodat2, int, dfd, const char __user *, filename,
umode_t, mode, unsigned int, flags)
{
return do_fchmodat(dfd, filename, mode, flags);
}
SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename,
umode_t, mode)
{
return do_fchmodat(dfd, filename, mode, 0);
}
SYSCALL_DEFINE2(chmod, const char __user *, filename, umode_t, mode)
[PATCH] vfs: *at functions: core Here is a series of patches which introduce in total 13 new system calls which take a file descriptor/filename pair instead of a single file name. These functions, openat etc, have been discussed on numerous occasions. They are needed to implement race-free filesystem traversal, they are necessary to implement a virtual per-thread current working directory (think multi-threaded backup software), etc. We have in glibc today implementations of the interfaces which use the /proc/self/fd magic. But this code is rather expensive. Here are some results (similar to what Jim Meyering posted before). The test creates a deep directory hierarchy on a tmpfs filesystem. Then rm -fr is used to remove all directories. Without syscall support I get this: real 0m31.921s user 0m0.688s sys 0m31.234s With syscall support the results are much better: real 0m20.699s user 0m0.536s sys 0m20.149s The interfaces are for obvious reasons currently not much used. But they'll be used. coreutils (and Jeff's posixutils) are already using them. Furthermore, code like ftw/fts in libc (maybe even glob) will also start using them. I expect a patch to make follow soon. Every program which is walking the filesystem tree will benefit. Signed-off-by: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@ftp.linux.org.uk> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-19 04:43:53 +03:00
{
return do_fchmodat(AT_FDCWD, filename, mode, 0);
[PATCH] vfs: *at functions: core Here is a series of patches which introduce in total 13 new system calls which take a file descriptor/filename pair instead of a single file name. These functions, openat etc, have been discussed on numerous occasions. They are needed to implement race-free filesystem traversal, they are necessary to implement a virtual per-thread current working directory (think multi-threaded backup software), etc. We have in glibc today implementations of the interfaces which use the /proc/self/fd magic. But this code is rather expensive. Here are some results (similar to what Jim Meyering posted before). The test creates a deep directory hierarchy on a tmpfs filesystem. Then rm -fr is used to remove all directories. Without syscall support I get this: real 0m31.921s user 0m0.688s sys 0m31.234s With syscall support the results are much better: real 0m20.699s user 0m0.536s sys 0m20.149s The interfaces are for obvious reasons currently not much used. But they'll be used. coreutils (and Jeff's posixutils) are already using them. Furthermore, code like ftw/fts in libc (maybe even glob) will also start using them. I expect a patch to make follow soon. Every program which is walking the filesystem tree will benefit. Signed-off-by: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@ftp.linux.org.uk> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-19 04:43:53 +03:00
}
/*
attr: port attribute changes to new types Now that we introduced new infrastructure to increase the type safety for filesystems supporting idmapped mounts port the first part of the vfs over to them. This ports the attribute changes codepaths to rely on the new better helpers using a dedicated type. Before this change we used to take a shortcut and place the actual values that would be written to inode->i_{g,u}id into struct iattr. This had the advantage that we moved idmappings mostly out of the picture early on but it made reasoning about changes more difficult than it should be. The filesystem was never explicitly told that it dealt with an idmapped mount. The transition to the value that needed to be stored in inode->i_{g,u}id appeared way too early and increased the probability of bugs in various codepaths. We know place the same value in struct iattr no matter if this is an idmapped mount or not. The vfs will only deal with type safe vfs{g,u}id_t. This makes it massively safer to perform permission checks as the type will tell us what checks we need to perform and what helpers we need to use. Fileystems raising FS_ALLOW_IDMAP can't simply write ia_vfs{g,u}id to inode->i_{g,u}id since they are different types. Instead they need to use the dedicated vfs{g,u}id_to_k{g,u}id() helpers that map the vfs{g,u}id into the filesystem. The other nice effect is that filesystems like overlayfs don't need to care about idmappings explicitly anymore and can simply set up struct iattr accordingly directly. Link: https://lore.kernel.org/lkml/CAHk-=win6+ahs1EwLkcq8apqLi_1wXFWbrPf340zYEhObpz4jA@mail.gmail.com [1] Link: https://lore.kernel.org/r/20220621141454.2914719-9-brauner@kernel.org Cc: Seth Forshee <sforshee@digitalocean.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aleksa Sarai <cyphar@cyphar.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> CC: linux-fsdevel@vger.kernel.org Reviewed-by: Seth Forshee <sforshee@digitalocean.com> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-06-21 17:14:54 +03:00
* Check whether @kuid is valid and if so generate and set vfsuid_t in
* ia_vfsuid.
*
* Return: true if @kuid is valid, false if not.
*/
static inline bool setattr_vfsuid(struct iattr *attr, kuid_t kuid)
{
if (!uid_valid(kuid))
return false;
attr->ia_valid |= ATTR_UID;
attr->ia_vfsuid = VFSUIDT_INIT(kuid);
return true;
}
/*
attr: port attribute changes to new types Now that we introduced new infrastructure to increase the type safety for filesystems supporting idmapped mounts port the first part of the vfs over to them. This ports the attribute changes codepaths to rely on the new better helpers using a dedicated type. Before this change we used to take a shortcut and place the actual values that would be written to inode->i_{g,u}id into struct iattr. This had the advantage that we moved idmappings mostly out of the picture early on but it made reasoning about changes more difficult than it should be. The filesystem was never explicitly told that it dealt with an idmapped mount. The transition to the value that needed to be stored in inode->i_{g,u}id appeared way too early and increased the probability of bugs in various codepaths. We know place the same value in struct iattr no matter if this is an idmapped mount or not. The vfs will only deal with type safe vfs{g,u}id_t. This makes it massively safer to perform permission checks as the type will tell us what checks we need to perform and what helpers we need to use. Fileystems raising FS_ALLOW_IDMAP can't simply write ia_vfs{g,u}id to inode->i_{g,u}id since they are different types. Instead they need to use the dedicated vfs{g,u}id_to_k{g,u}id() helpers that map the vfs{g,u}id into the filesystem. The other nice effect is that filesystems like overlayfs don't need to care about idmappings explicitly anymore and can simply set up struct iattr accordingly directly. Link: https://lore.kernel.org/lkml/CAHk-=win6+ahs1EwLkcq8apqLi_1wXFWbrPf340zYEhObpz4jA@mail.gmail.com [1] Link: https://lore.kernel.org/r/20220621141454.2914719-9-brauner@kernel.org Cc: Seth Forshee <sforshee@digitalocean.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aleksa Sarai <cyphar@cyphar.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> CC: linux-fsdevel@vger.kernel.org Reviewed-by: Seth Forshee <sforshee@digitalocean.com> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-06-21 17:14:54 +03:00
* Check whether @kgid is valid and if so generate and set vfsgid_t in
* ia_vfsgid.
*
* Return: true if @kgid is valid, false if not.
*/
static inline bool setattr_vfsgid(struct iattr *attr, kgid_t kgid)
{
if (!gid_valid(kgid))
return false;
attr->ia_valid |= ATTR_GID;
attr->ia_vfsgid = VFSGIDT_INIT(kgid);
return true;
}
int chown_common(const struct path *path, uid_t user, gid_t group)
{
struct mnt_idmap *idmap;
struct user_namespace *fs_userns;
struct inode *inode = path->dentry->d_inode;
struct inode *delegated_inode = NULL;
int error;
struct iattr newattrs;
kuid_t uid;
kgid_t gid;
uid = make_kuid(current_user_ns(), user);
gid = make_kgid(current_user_ns(), group);
idmap = mnt_idmap(path->mnt);
fs: support mapped mounts of mapped filesystems In previous patches we added new and modified existing helpers to handle idmapped mounts of filesystems mounted with an idmapping. In this final patch we convert all relevant places in the vfs to actually pass the filesystem's idmapping into these helpers. With this the vfs is in shape to handle idmapped mounts of filesystems mounted with an idmapping. Note that this is just the generic infrastructure. Actually adding support for idmapped mounts to a filesystem mountable with an idmapping is follow-up work. In this patch we extend the definition of an idmapped mount from a mount that that has the initial idmapping attached to it to a mount that has an idmapping attached to it which is not the same as the idmapping the filesystem was mounted with. As before we do not allow the initial idmapping to be attached to a mount. In addition this patch prevents that the idmapping the filesystem was mounted with can be attached to a mount created based on this filesystem. This has multiple reasons and advantages. First, attaching the initial idmapping or the filesystem's idmapping doesn't make much sense as in both cases the values of the i_{g,u}id and other places where k{g,u}ids are used do not change. Second, a user that really wants to do this for whatever reason can just create a separate dedicated identical idmapping to attach to the mount. Third, we can continue to use the initial idmapping as an indicator that a mount is not idmapped allowing us to continue to keep passing the initial idmapping into the mapping helpers to tell them that something isn't an idmapped mount even if the filesystem is mounted with an idmapping. Link: https://lore.kernel.org/r/20211123114227.3124056-11-brauner@kernel.org (v1) Link: https://lore.kernel.org/r/20211130121032.3753852-11-brauner@kernel.org (v2) Link: https://lore.kernel.org/r/20211203111707.3901969-11-brauner@kernel.org Cc: Seth Forshee <sforshee@digitalocean.com> Cc: Amir Goldstein <amir73il@gmail.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@zeniv.linux.org.uk> CC: linux-fsdevel@vger.kernel.org Reviewed-by: Seth Forshee <sforshee@digitalocean.com> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-12-03 14:17:07 +03:00
fs_userns = i_user_ns(inode);
NFS: fix BUG() crash in notify_change() with patch to chown_common() We have observed a BUG() crash in fs/attr.c:notify_change(). The crash occurs during an rsync into a filesystem that is exported via NFS. 1.) fs/attr.c:notify_change() modifies the caller's version of attr. 2.) 6de0ec00ba8d ("VFS: make notify_change pass ATTR_KILL_S*ID to setattr operations") introduced a BUG() restriction such that "no function will ever call notify_change() with both ATTR_MODE and ATTR_KILL_S*ID set". Under some circumstances though, it will have assisted in setting the caller's version of attr to this very combination. 3.) 27ac0ffeac80 ("locks: break delegations on any attribute modification") introduced code to handle breaking delegations. This can result in notify_change() being re-called. attr _must_ be explicitly reset to avoid triggering the BUG() established in #2. 4.) The path that that triggers this is via fs/open.c:chmod_common(). The combination of attr flags set here and in the first call to notify_change() along with a later failed break_deleg_wait() results in notify_change() being called again via retry_deleg without resetting attr. Solution is to move retry_deleg in chmod_common() a bit further up to ensure attr is completely reset. There are other places where this seemingly could occur, such as fs/utimes.c:utimes_common(), but the attr flags are not initially set in such a way to trigger this. Fixes: 27ac0ffeac80 ("locks: break delegations on any attribute modification") Reported-by: Eric Meddaugh <etmsys@rit.edu> Tested-by: Eric Meddaugh <etmsys@rit.edu> Signed-off-by: Andrew Elble <aweits@rit.edu> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2015-02-23 16:51:24 +03:00
retry_deleg:
newattrs.ia_vfsuid = INVALID_VFSUID;
newattrs.ia_vfsgid = INVALID_VFSGID;
newattrs.ia_valid = ATTR_CTIME;
attr: port attribute changes to new types Now that we introduced new infrastructure to increase the type safety for filesystems supporting idmapped mounts port the first part of the vfs over to them. This ports the attribute changes codepaths to rely on the new better helpers using a dedicated type. Before this change we used to take a shortcut and place the actual values that would be written to inode->i_{g,u}id into struct iattr. This had the advantage that we moved idmappings mostly out of the picture early on but it made reasoning about changes more difficult than it should be. The filesystem was never explicitly told that it dealt with an idmapped mount. The transition to the value that needed to be stored in inode->i_{g,u}id appeared way too early and increased the probability of bugs in various codepaths. We know place the same value in struct iattr no matter if this is an idmapped mount or not. The vfs will only deal with type safe vfs{g,u}id_t. This makes it massively safer to perform permission checks as the type will tell us what checks we need to perform and what helpers we need to use. Fileystems raising FS_ALLOW_IDMAP can't simply write ia_vfs{g,u}id to inode->i_{g,u}id since they are different types. Instead they need to use the dedicated vfs{g,u}id_to_k{g,u}id() helpers that map the vfs{g,u}id into the filesystem. The other nice effect is that filesystems like overlayfs don't need to care about idmappings explicitly anymore and can simply set up struct iattr accordingly directly. Link: https://lore.kernel.org/lkml/CAHk-=win6+ahs1EwLkcq8apqLi_1wXFWbrPf340zYEhObpz4jA@mail.gmail.com [1] Link: https://lore.kernel.org/r/20220621141454.2914719-9-brauner@kernel.org Cc: Seth Forshee <sforshee@digitalocean.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aleksa Sarai <cyphar@cyphar.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> CC: linux-fsdevel@vger.kernel.org Reviewed-by: Seth Forshee <sforshee@digitalocean.com> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-06-21 17:14:54 +03:00
if ((user != (uid_t)-1) && !setattr_vfsuid(&newattrs, uid))
return -EINVAL;
if ((group != (gid_t)-1) && !setattr_vfsgid(&newattrs, gid))
return -EINVAL;
inode_lock(inode);
attr: use consistent sgid stripping checks Currently setgid stripping in file_remove_privs()'s should_remove_suid() helper is inconsistent with other parts of the vfs. Specifically, it only raises ATTR_KILL_SGID if the inode is S_ISGID and S_IXGRP but not if the inode isn't in the caller's groups and the caller isn't privileged over the inode although we require this already in setattr_prepare() and setattr_copy() and so all filesystem implement this requirement implicitly because they have to use setattr_{prepare,copy}() anyway. But the inconsistency shows up in setgid stripping bugs for overlayfs in xfstests (e.g., generic/673, generic/683, generic/685, generic/686, generic/687). For example, we test whether suid and setgid stripping works correctly when performing various write-like operations as an unprivileged user (fallocate, reflink, write, etc.): echo "Test 1 - qa_user, non-exec file $verb" setup_testfile chmod a+rws $junk_file commit_and_check "$qa_user" "$verb" 64k 64k The test basically creates a file with 6666 permissions. While the file has the S_ISUID and S_ISGID bits set it does not have the S_IXGRP set. On a regular filesystem like xfs what will happen is: sys_fallocate() -> vfs_fallocate() -> xfs_file_fallocate() -> file_modified() -> __file_remove_privs() -> dentry_needs_remove_privs() -> should_remove_suid() -> __remove_privs() newattrs.ia_valid = ATTR_FORCE | kill; -> notify_change() -> setattr_copy() In should_remove_suid() we can see that ATTR_KILL_SUID is raised unconditionally because the file in the test has S_ISUID set. But we also see that ATTR_KILL_SGID won't be set because while the file is S_ISGID it is not S_IXGRP (see above) which is a condition for ATTR_KILL_SGID being raised. So by the time we call notify_change() we have attr->ia_valid set to ATTR_KILL_SUID | ATTR_FORCE. Now notify_change() sees that ATTR_KILL_SUID is set and does: ia_valid = attr->ia_valid |= ATTR_MODE attr->ia_mode = (inode->i_mode & ~S_ISUID); which means that when we call setattr_copy() later we will definitely update inode->i_mode. Note that attr->ia_mode still contains S_ISGID. Now we call into the filesystem's ->setattr() inode operation which will end up calling setattr_copy(). Since ATTR_MODE is set we will hit: if (ia_valid & ATTR_MODE) { umode_t mode = attr->ia_mode; vfsgid_t vfsgid = i_gid_into_vfsgid(mnt_userns, inode); if (!vfsgid_in_group_p(vfsgid) && !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID)) mode &= ~S_ISGID; inode->i_mode = mode; } and since the caller in the test is neither capable nor in the group of the inode the S_ISGID bit is stripped. But assume the file isn't suid then ATTR_KILL_SUID won't be raised which has the consequence that neither the setgid nor the suid bits are stripped even though it should be stripped because the inode isn't in the caller's groups and the caller isn't privileged over the inode. If overlayfs is in the mix things become a bit more complicated and the bug shows up more clearly. When e.g., ovl_setattr() is hit from ovl_fallocate()'s call to file_remove_privs() then ATTR_KILL_SUID and ATTR_KILL_SGID might be raised but because the check in notify_change() is questioning the ATTR_KILL_SGID flag again by requiring S_IXGRP for it to be stripped the S_ISGID bit isn't removed even though it should be stripped: sys_fallocate() -> vfs_fallocate() -> ovl_fallocate() -> file_remove_privs() -> dentry_needs_remove_privs() -> should_remove_suid() -> __remove_privs() newattrs.ia_valid = ATTR_FORCE | kill; -> notify_change() -> ovl_setattr() // TAKE ON MOUNTER'S CREDS -> ovl_do_notify_change() -> notify_change() // GIVE UP MOUNTER'S CREDS // TAKE ON MOUNTER'S CREDS -> vfs_fallocate() -> xfs_file_fallocate() -> file_modified() -> __file_remove_privs() -> dentry_needs_remove_privs() -> should_remove_suid() -> __remove_privs() newattrs.ia_valid = attr_force | kill; -> notify_change() The fix for all of this is to make file_remove_privs()'s should_remove_suid() helper to perform the same checks as we already require in setattr_prepare() and setattr_copy() and have notify_change() not pointlessly requiring S_IXGRP again. It doesn't make any sense in the first place because the caller must calculate the flags via should_remove_suid() anyway which would raise ATTR_KILL_SGID. While we're at it we move should_remove_suid() from inode.c to attr.c where it belongs with the rest of the iattr helpers. Especially since it returns ATTR_KILL_S{G,U}ID flags. We also rename it to setattr_should_drop_suidgid() to better reflect that it indicates both setuid and setgid bit removal and also that it returns attr flags. Running xfstests with this doesn't report any regressions. We should really try and use consistent checks. Reviewed-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-10-17 18:06:37 +03:00
if (!S_ISDIR(inode->i_mode))
newattrs.ia_valid |= ATTR_KILL_SUID | ATTR_KILL_PRIV |
setattr_should_drop_sgid(idmap, inode);
attr: port attribute changes to new types Now that we introduced new infrastructure to increase the type safety for filesystems supporting idmapped mounts port the first part of the vfs over to them. This ports the attribute changes codepaths to rely on the new better helpers using a dedicated type. Before this change we used to take a shortcut and place the actual values that would be written to inode->i_{g,u}id into struct iattr. This had the advantage that we moved idmappings mostly out of the picture early on but it made reasoning about changes more difficult than it should be. The filesystem was never explicitly told that it dealt with an idmapped mount. The transition to the value that needed to be stored in inode->i_{g,u}id appeared way too early and increased the probability of bugs in various codepaths. We know place the same value in struct iattr no matter if this is an idmapped mount or not. The vfs will only deal with type safe vfs{g,u}id_t. This makes it massively safer to perform permission checks as the type will tell us what checks we need to perform and what helpers we need to use. Fileystems raising FS_ALLOW_IDMAP can't simply write ia_vfs{g,u}id to inode->i_{g,u}id since they are different types. Instead they need to use the dedicated vfs{g,u}id_to_k{g,u}id() helpers that map the vfs{g,u}id into the filesystem. The other nice effect is that filesystems like overlayfs don't need to care about idmappings explicitly anymore and can simply set up struct iattr accordingly directly. Link: https://lore.kernel.org/lkml/CAHk-=win6+ahs1EwLkcq8apqLi_1wXFWbrPf340zYEhObpz4jA@mail.gmail.com [1] Link: https://lore.kernel.org/r/20220621141454.2914719-9-brauner@kernel.org Cc: Seth Forshee <sforshee@digitalocean.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aleksa Sarai <cyphar@cyphar.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> CC: linux-fsdevel@vger.kernel.org Reviewed-by: Seth Forshee <sforshee@digitalocean.com> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-06-21 17:14:54 +03:00
/* Continue to send actual fs values, not the mount values. */
error = security_path_chown(
path,
from_vfsuid(idmap, fs_userns, newattrs.ia_vfsuid),
from_vfsgid(idmap, fs_userns, newattrs.ia_vfsgid));
if (!error)
error = notify_change(idmap, path->dentry, &newattrs,
&delegated_inode);
inode_unlock(inode);
if (delegated_inode) {
error = break_deleg_wait(&delegated_inode);
if (!error)
goto retry_deleg;
}
return error;
}
int do_fchownat(int dfd, const char __user *filename, uid_t user, gid_t group,
int flag)
[PATCH] vfs: *at functions: core Here is a series of patches which introduce in total 13 new system calls which take a file descriptor/filename pair instead of a single file name. These functions, openat etc, have been discussed on numerous occasions. They are needed to implement race-free filesystem traversal, they are necessary to implement a virtual per-thread current working directory (think multi-threaded backup software), etc. We have in glibc today implementations of the interfaces which use the /proc/self/fd magic. But this code is rather expensive. Here are some results (similar to what Jim Meyering posted before). The test creates a deep directory hierarchy on a tmpfs filesystem. Then rm -fr is used to remove all directories. Without syscall support I get this: real 0m31.921s user 0m0.688s sys 0m31.234s With syscall support the results are much better: real 0m20.699s user 0m0.536s sys 0m20.149s The interfaces are for obvious reasons currently not much used. But they'll be used. coreutils (and Jeff's posixutils) are already using them. Furthermore, code like ftw/fts in libc (maybe even glob) will also start using them. I expect a patch to make follow soon. Every program which is walking the filesystem tree will benefit. Signed-off-by: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@ftp.linux.org.uk> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-19 04:43:53 +03:00
{
struct path path;
[PATCH] vfs: *at functions: core Here is a series of patches which introduce in total 13 new system calls which take a file descriptor/filename pair instead of a single file name. These functions, openat etc, have been discussed on numerous occasions. They are needed to implement race-free filesystem traversal, they are necessary to implement a virtual per-thread current working directory (think multi-threaded backup software), etc. We have in glibc today implementations of the interfaces which use the /proc/self/fd magic. But this code is rather expensive. Here are some results (similar to what Jim Meyering posted before). The test creates a deep directory hierarchy on a tmpfs filesystem. Then rm -fr is used to remove all directories. Without syscall support I get this: real 0m31.921s user 0m0.688s sys 0m31.234s With syscall support the results are much better: real 0m20.699s user 0m0.536s sys 0m20.149s The interfaces are for obvious reasons currently not much used. But they'll be used. coreutils (and Jeff's posixutils) are already using them. Furthermore, code like ftw/fts in libc (maybe even glob) will also start using them. I expect a patch to make follow soon. Every program which is walking the filesystem tree will benefit. Signed-off-by: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@ftp.linux.org.uk> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-19 04:43:53 +03:00
int error = -EINVAL;
int lookup_flags;
[PATCH] vfs: *at functions: core Here is a series of patches which introduce in total 13 new system calls which take a file descriptor/filename pair instead of a single file name. These functions, openat etc, have been discussed on numerous occasions. They are needed to implement race-free filesystem traversal, they are necessary to implement a virtual per-thread current working directory (think multi-threaded backup software), etc. We have in glibc today implementations of the interfaces which use the /proc/self/fd magic. But this code is rather expensive. Here are some results (similar to what Jim Meyering posted before). The test creates a deep directory hierarchy on a tmpfs filesystem. Then rm -fr is used to remove all directories. Without syscall support I get this: real 0m31.921s user 0m0.688s sys 0m31.234s With syscall support the results are much better: real 0m20.699s user 0m0.536s sys 0m20.149s The interfaces are for obvious reasons currently not much used. But they'll be used. coreutils (and Jeff's posixutils) are already using them. Furthermore, code like ftw/fts in libc (maybe even glob) will also start using them. I expect a patch to make follow soon. Every program which is walking the filesystem tree will benefit. Signed-off-by: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@ftp.linux.org.uk> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-19 04:43:53 +03:00
if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
[PATCH] vfs: *at functions: core Here is a series of patches which introduce in total 13 new system calls which take a file descriptor/filename pair instead of a single file name. These functions, openat etc, have been discussed on numerous occasions. They are needed to implement race-free filesystem traversal, they are necessary to implement a virtual per-thread current working directory (think multi-threaded backup software), etc. We have in glibc today implementations of the interfaces which use the /proc/self/fd magic. But this code is rather expensive. Here are some results (similar to what Jim Meyering posted before). The test creates a deep directory hierarchy on a tmpfs filesystem. Then rm -fr is used to remove all directories. Without syscall support I get this: real 0m31.921s user 0m0.688s sys 0m31.234s With syscall support the results are much better: real 0m20.699s user 0m0.536s sys 0m20.149s The interfaces are for obvious reasons currently not much used. But they'll be used. coreutils (and Jeff's posixutils) are already using them. Furthermore, code like ftw/fts in libc (maybe even glob) will also start using them. I expect a patch to make follow soon. Every program which is walking the filesystem tree will benefit. Signed-off-by: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@ftp.linux.org.uk> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-19 04:43:53 +03:00
goto out;
lookup_flags = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
if (flag & AT_EMPTY_PATH)
lookup_flags |= LOOKUP_EMPTY;
retry:
error = user_path_at(dfd, filename, lookup_flags, &path);
if (error)
goto out;
error = mnt_want_write(path.mnt);
if (error)
goto out_release;
error = chown_common(&path, user, group);
mnt_drop_write(path.mnt);
out_release:
path_put(&path);
if (retry_estale(error, lookup_flags)) {
lookup_flags |= LOOKUP_REVAL;
goto retry;
}
[PATCH] vfs: *at functions: core Here is a series of patches which introduce in total 13 new system calls which take a file descriptor/filename pair instead of a single file name. These functions, openat etc, have been discussed on numerous occasions. They are needed to implement race-free filesystem traversal, they are necessary to implement a virtual per-thread current working directory (think multi-threaded backup software), etc. We have in glibc today implementations of the interfaces which use the /proc/self/fd magic. But this code is rather expensive. Here are some results (similar to what Jim Meyering posted before). The test creates a deep directory hierarchy on a tmpfs filesystem. Then rm -fr is used to remove all directories. Without syscall support I get this: real 0m31.921s user 0m0.688s sys 0m31.234s With syscall support the results are much better: real 0m20.699s user 0m0.536s sys 0m20.149s The interfaces are for obvious reasons currently not much used. But they'll be used. coreutils (and Jeff's posixutils) are already using them. Furthermore, code like ftw/fts in libc (maybe even glob) will also start using them. I expect a patch to make follow soon. Every program which is walking the filesystem tree will benefit. Signed-off-by: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@ftp.linux.org.uk> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-19 04:43:53 +03:00
out:
return error;
}
SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,
gid_t, group, int, flag)
{
return do_fchownat(dfd, filename, user, group, flag);
}
SYSCALL_DEFINE3(chown, const char __user *, filename, uid_t, user, gid_t, group)
{
return do_fchownat(AT_FDCWD, filename, user, group, 0);
}
SYSCALL_DEFINE3(lchown, const char __user *, filename, uid_t, user, gid_t, group)
{
return do_fchownat(AT_FDCWD, filename, user, group,
AT_SYMLINK_NOFOLLOW);
}
int vfs_fchown(struct file *file, uid_t user, gid_t group)
{
int error;
error = mnt_want_write_file(file);
if (error)
return error;
audit_file(file);
error = chown_common(&file->f_path, user, group);
mnt_drop_write_file(file);
return error;
}
int ksys_fchown(unsigned int fd, uid_t user, gid_t group)
{
struct fd f = fdget(fd);
int error = -EBADF;
if (f.file) {
error = vfs_fchown(f.file, user, group);
fdput(f);
}
return error;
}
SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group)
{
return ksys_fchown(fd, user, group);
}
static inline int file_get_write_access(struct file *f)
{
int error;
error = get_write_access(f->f_inode);
if (unlikely(error))
return error;
error = mnt_get_write_access(f->f_path.mnt);
if (unlikely(error))
goto cleanup_inode;
if (unlikely(f->f_mode & FMODE_BACKING)) {
error = mnt_get_write_access(backing_file_user_path(f)->mnt);
if (unlikely(error))
goto cleanup_mnt;
}
return 0;
cleanup_mnt:
mnt_put_write_access(f->f_path.mnt);
cleanup_inode:
put_write_access(f->f_inode);
return error;
}
static int do_dentry_open(struct file *f,
overlayfs: Make f_path always point to the overlay and f_inode to the underlay Make file->f_path always point to the overlay dentry so that the path in /proc/pid/fd is correct and to ensure that label-based LSMs have access to the overlay as well as the underlay (path-based LSMs probably don't need it). Using my union testsuite to set things up, before the patch I see: [root@andromeda union-testsuite]# bash 5</mnt/a/foo107 [root@andromeda union-testsuite]# ls -l /proc/$$/fd/ ... lr-x------. 1 root root 64 Jun 5 14:38 5 -> /a/foo107 [root@andromeda union-testsuite]# stat /mnt/a/foo107 ... Device: 23h/35d Inode: 13381 Links: 1 ... [root@andromeda union-testsuite]# stat -L /proc/$$/fd/5 ... Device: 23h/35d Inode: 13381 Links: 1 ... After the patch: [root@andromeda union-testsuite]# bash 5</mnt/a/foo107 [root@andromeda union-testsuite]# ls -l /proc/$$/fd/ ... lr-x------. 1 root root 64 Jun 5 14:22 5 -> /mnt/a/foo107 [root@andromeda union-testsuite]# stat /mnt/a/foo107 ... Device: 23h/35d Inode: 40346 Links: 1 ... [root@andromeda union-testsuite]# stat -L /proc/$$/fd/5 ... Device: 23h/35d Inode: 40346 Links: 1 ... Note the change in where /proc/$$/fd/5 points to in the ls command. It was pointing to /a/foo107 (which doesn't exist) and now points to /mnt/a/foo107 (which is correct). The inode accessed, however, is the lower layer. The union layer is on device 25h/37d and the upper layer on 24h/36d. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2015-06-18 16:32:31 +03:00
struct inode *inode,
int (*open)(struct inode *, struct file *))
{
2011-03-13 10:51:11 +03:00
static const struct file_operations empty_fops = {};
int error;
path_get(&f->f_path);
overlayfs: Make f_path always point to the overlay and f_inode to the underlay Make file->f_path always point to the overlay dentry so that the path in /proc/pid/fd is correct and to ensure that label-based LSMs have access to the overlay as well as the underlay (path-based LSMs probably don't need it). Using my union testsuite to set things up, before the patch I see: [root@andromeda union-testsuite]# bash 5</mnt/a/foo107 [root@andromeda union-testsuite]# ls -l /proc/$$/fd/ ... lr-x------. 1 root root 64 Jun 5 14:38 5 -> /a/foo107 [root@andromeda union-testsuite]# stat /mnt/a/foo107 ... Device: 23h/35d Inode: 13381 Links: 1 ... [root@andromeda union-testsuite]# stat -L /proc/$$/fd/5 ... Device: 23h/35d Inode: 13381 Links: 1 ... After the patch: [root@andromeda union-testsuite]# bash 5</mnt/a/foo107 [root@andromeda union-testsuite]# ls -l /proc/$$/fd/ ... lr-x------. 1 root root 64 Jun 5 14:22 5 -> /mnt/a/foo107 [root@andromeda union-testsuite]# stat /mnt/a/foo107 ... Device: 23h/35d Inode: 40346 Links: 1 ... [root@andromeda union-testsuite]# stat -L /proc/$$/fd/5 ... Device: 23h/35d Inode: 40346 Links: 1 ... Note the change in where /proc/$$/fd/5 points to in the ls command. It was pointing to /a/foo107 (which doesn't exist) and now points to /mnt/a/foo107 (which is correct). The inode accessed, however, is the lower layer. The union layer is on device 25h/37d and the upper layer on 24h/36d. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2015-06-18 16:32:31 +03:00
f->f_inode = inode;
f->f_mapping = inode->i_mapping;
fs: new infrastructure for writeback error handling and reporting Most filesystems currently use mapping_set_error and filemap_check_errors for setting and reporting/clearing writeback errors at the mapping level. filemap_check_errors is indirectly called from most of the filemap_fdatawait_* functions and from filemap_write_and_wait*. These functions are called from all sorts of contexts to wait on writeback to finish -- e.g. mostly in fsync, but also in truncate calls, getattr, etc. The non-fsync callers are problematic. We should be reporting writeback errors during fsync, but many places spread over the tree clear out errors before they can be properly reported, or report errors at nonsensical times. If I get -EIO on a stat() call, there is no reason for me to assume that it is because some previous writeback failed. The fact that it also clears out the error such that a subsequent fsync returns 0 is a bug, and a nasty one since that's potentially silent data corruption. This patch adds a small bit of new infrastructure for setting and reporting errors during address_space writeback. While the above was my original impetus for adding this, I think it's also the case that current fsync semantics are just problematic for userland. Most applications that call fsync do so to ensure that the data they wrote has hit the backing store. In the case where there are multiple writers to the file at the same time, this is really hard to determine. The first one to call fsync will see any stored error, and the rest get back 0. The processes with open fds may not be associated with one another in any way. They could even be in different containers, so ensuring coordination between all fsync callers is not really an option. One way to remedy this would be to track what file descriptor was used to dirty the file, but that's rather cumbersome and would likely be slow. However, there is a simpler way to improve the semantics here without incurring too much overhead. This set adds an errseq_t to struct address_space, and a corresponding one is added to struct file. Writeback errors are recorded in the mapping's errseq_t, and the one in struct file is used as the "since" value. This changes the semantics of the Linux fsync implementation such that applications can now use it to determine whether there were any writeback errors since fsync(fd) was last called (or since the file was opened in the case of fsync having never been called). Note that those writeback errors may have occurred when writing data that was dirtied via an entirely different fd, but that's the case now with the current mapping_set_error/filemap_check_error infrastructure. This will at least prevent you from getting a false report of success. The new behavior is still consistent with the POSIX spec, and is more reliable for application developers. This patch just adds some basic infrastructure for doing this, and ensures that the f_wb_err "cursor" is properly set when a file is opened. Later patches will change the existing code to use this new infrastructure for reporting errors at fsync time. Signed-off-by: Jeff Layton <jlayton@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz>
2017-07-06 14:02:25 +03:00
f->f_wb_err = filemap_sample_wb_err(f->f_mapping);
vfs: track per-sb writeback errors and report them to syncfs Patch series "vfs: have syncfs() return error when there are writeback errors", v6. Currently, syncfs does not return errors when one of the inodes fails to be written back. It will return errors based on the legacy AS_EIO and AS_ENOSPC flags when syncing out the block device fails, but that's not particularly helpful for filesystems that aren't backed by a blockdev. It's also possible for a stray sync to lose those errors. The basic idea in this set is to track writeback errors at the superblock level, so that we can quickly and easily check whether something bad happened without having to fsync each file individually. syncfs is then changed to reliably report writeback errors after they occur, much in the same fashion as fsync does now. This patch (of 2): Usually we suggest that applications call fsync when they want to ensure that all data written to the file has made it to the backing store, but that can be inefficient when there are a lot of open files. Calling syncfs on the filesystem can be more efficient in some situations, but the error reporting doesn't currently work the way most people expect. If a single inode on a filesystem reports a writeback error, syncfs won't necessarily return an error. syncfs only returns an error if __sync_blockdev fails, and on some filesystems that's a no-op. It would be better if syncfs reported an error if there were any writeback failures. Then applications could call syncfs to see if there are any errors on any open files, and could then call fsync on all of the other descriptors to figure out which one failed. This patch adds a new errseq_t to struct super_block, and has mapping_set_error also record writeback errors there. To report those errors, we also need to keep an errseq_t in struct file to act as a cursor. This patch adds a dedicated field for that purpose, which slots nicely into 4 bytes of padding at the end of struct file on x86_64. An earlier version of this patch used an O_PATH file descriptor to cue the kernel that the open file should track the superblock error and not the inode's writeback error. I think that API is just too weird though. This is simpler and should make syncfs error reporting "just work" even if someone is multiplexing fsync and syncfs on the same fds. Signed-off-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Andres Freund <andres@anarazel.de> Cc: Matthew Wilcox <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dave Chinner <david@fromorbit.com> Cc: David Howells <dhowells@redhat.com> Link: http://lkml.kernel.org/r/20200428135155.19223-1-jlayton@kernel.org Link: http://lkml.kernel.org/r/20200428135155.19223-2-jlayton@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-02 07:45:36 +03:00
f->f_sb_err = file_sample_sb_err(f);
fs: new infrastructure for writeback error handling and reporting Most filesystems currently use mapping_set_error and filemap_check_errors for setting and reporting/clearing writeback errors at the mapping level. filemap_check_errors is indirectly called from most of the filemap_fdatawait_* functions and from filemap_write_and_wait*. These functions are called from all sorts of contexts to wait on writeback to finish -- e.g. mostly in fsync, but also in truncate calls, getattr, etc. The non-fsync callers are problematic. We should be reporting writeback errors during fsync, but many places spread over the tree clear out errors before they can be properly reported, or report errors at nonsensical times. If I get -EIO on a stat() call, there is no reason for me to assume that it is because some previous writeback failed. The fact that it also clears out the error such that a subsequent fsync returns 0 is a bug, and a nasty one since that's potentially silent data corruption. This patch adds a small bit of new infrastructure for setting and reporting errors during address_space writeback. While the above was my original impetus for adding this, I think it's also the case that current fsync semantics are just problematic for userland. Most applications that call fsync do so to ensure that the data they wrote has hit the backing store. In the case where there are multiple writers to the file at the same time, this is really hard to determine. The first one to call fsync will see any stored error, and the rest get back 0. The processes with open fds may not be associated with one another in any way. They could even be in different containers, so ensuring coordination between all fsync callers is not really an option. One way to remedy this would be to track what file descriptor was used to dirty the file, but that's rather cumbersome and would likely be slow. However, there is a simpler way to improve the semantics here without incurring too much overhead. This set adds an errseq_t to struct address_space, and a corresponding one is added to struct file. Writeback errors are recorded in the mapping's errseq_t, and the one in struct file is used as the "since" value. This changes the semantics of the Linux fsync implementation such that applications can now use it to determine whether there were any writeback errors since fsync(fd) was last called (or since the file was opened in the case of fsync having never been called). Note that those writeback errors may have occurred when writing data that was dirtied via an entirely different fd, but that's the case now with the current mapping_set_error/filemap_check_error infrastructure. This will at least prevent you from getting a false report of success. The new behavior is still consistent with the POSIX spec, and is more reliable for application developers. This patch just adds some basic infrastructure for doing this, and ensures that the f_wb_err "cursor" is properly set when a file is opened. Later patches will change the existing code to use this new infrastructure for reporting errors at fsync time. Signed-off-by: Jeff Layton <jlayton@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz>
2017-07-06 14:02:25 +03:00
if (unlikely(f->f_flags & O_PATH)) {
f->f_mode = FMODE_PATH | FMODE_OPENED;
2011-03-13 10:51:11 +03:00
f->f_op = &empty_fops;
return 0;
2011-03-13 10:51:11 +03:00
}
if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) {
i_readcount_inc(inode);
} else if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
error = file_get_write_access(f);
if (unlikely(error))
goto cleanup_file;
f->f_mode |= FMODE_WRITER;
}
Revert "vfs: properly and reliably lock f_pos in fdget_pos()" This reverts commit 0be0ee71816b2b6725e2b4f32ad6726c9d729777. I was hoping it would be benign to switch over entirely to FMODE_STREAM, and we'd have just a couple of small fixups we'd need, but it looks like we're not quite there yet. While it worked fine on both my desktop and laptop, they are fairly similar in other respects, and run mostly the same loads. Kenneth Crudup reports that it seems to break both his vmware installation and the KDE upower service. In both cases apparently leading to timeouts due to waitinmg for the f_pos lock. There are a number of character devices in particular that definitely want stream-like behavior, but that currently don't get marked as streams, and as a result get the exclusion between concurrent read()/write() on the same file descriptor. Which doesn't work well for them. The most obvious example if this is /dev/console and /dev/tty, which use console_fops and tty_fops respectively (and ptmx_fops for the pty master side). It may be that it's just this that causes problems, but we clearly weren't ready yet. Because there's a number of other likely common cases that don't have llseek implementations and would seem to act as stream devices: /dev/fuse (fuse_dev_operations) /dev/mcelog (mce_chrdev_ops) /dev/mei0 (mei_fops) /dev/net/tun (tun_fops) /dev/nvme0 (nvme_dev_fops) /dev/tpm0 (tpm_fops) /proc/self/ns/mnt (ns_file_operations) /dev/snd/pcm* (snd_pcm_f_ops[]) and while some of these could be trivially automatically detected by the vfs layer when the character device is opened by just noticing that they have no read or write operations either, it often isn't that obvious. Some character devices most definitely do use the file position, even if they don't allow seeking: the firmware update code, for example, uses simple_read_from_buffer() that does use f_pos, but doesn't allow seeking back and forth. We'll revisit this when there's a better way to detect the problem and fix it (possibly with a coccinelle script to do more of the FMODE_STREAM annotations). Reported-by: Kenneth R. Crudup <kenny@panix.com> Cc: Kirill Smelkov <kirr@nexedi.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-11-26 22:34:06 +03:00
/* POSIX.1-2008/SUSv4 Section XSI 2.9.7 */
if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode))
f->f_mode |= FMODE_ATOMIC_POS;
2011-03-13 10:51:11 +03:00
f->f_op = fops_get(inode->i_fop);
if (WARN_ON(!f->f_op)) {
error = -ENODEV;
goto cleanup_all;
}
2011-03-13 10:51:11 +03:00
error = security_file_open(f);
if (error)
goto cleanup_all;
error = break_lease(file_inode(f), f->f_flags);
if (error)
goto cleanup_all;
/* normally all 3 are set; ->open() can clear them if needed */
f->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
if (!open)
open = f->f_op->open;
if (open) {
error = open(inode, f);
if (error)
goto cleanup_all;
}
f->f_mode |= FMODE_OPENED;
if ((f->f_mode & FMODE_READ) &&
likely(f->f_op->read || f->f_op->read_iter))
f->f_mode |= FMODE_CAN_READ;
if ((f->f_mode & FMODE_WRITE) &&
likely(f->f_op->write || f->f_op->write_iter))
f->f_mode |= FMODE_CAN_WRITE;
if ((f->f_mode & FMODE_LSEEK) && !f->f_op->llseek)
f->f_mode &= ~FMODE_LSEEK;
if (f->f_mapping->a_ops && f->f_mapping->a_ops->direct_IO)
f->f_mode |= FMODE_CAN_ODIRECT;
f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
f->f_iocb_flags = iocb_flags(f);
file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);
if ((f->f_flags & O_DIRECT) && !(f->f_mode & FMODE_CAN_ODIRECT))
return -EINVAL;
/*
* XXX: Huge page cache doesn't support writing yet. Drop all page
* cache for this file before processing writes.
*/
mm, thp: relax the VM_DENYWRITE constraint on file-backed THPs Transparent huge pages are supported for read-only non-shmem files, but are only used for vmas with VM_DENYWRITE. This condition ensures that file THPs are protected from writes while an application is running (ETXTBSY). Any existing file THPs are then dropped from the page cache when a file is opened for write in do_dentry_open(). Since sys_mmap ignores MAP_DENYWRITE, this constrains the use of file THPs to vmas produced by execve(). Systems that make heavy use of shared libraries (e.g. Android) are unable to apply VM_DENYWRITE through the dynamic linker, preventing them from benefiting from the resultant reduced contention on the TLB. This patch reduces the constraint on file THPs allowing use with any executable mapping from a file not opened for write (see inode_is_open_for_write()). It also introduces additional conditions to ensure that files opened for write will never be backed by file THPs. Restricting the use of THPs to executable mappings eliminates the risk that a read-only file later opened for write would encounter significant latencies due to page cache truncation. The ld linker flag '-z max-page-size=(hugepage size)' can be used to produce executables with the necessary layout. The dynamic linker must map these file's segments at a hugepage size aligned vma for the mapping to be backed with THPs. Comparison of the performance characteristics of 4KB and 2MB-backed libraries follows; the Android dex2oat tool was used to AOT compile an example application on a single ARM core. 4KB Pages: ========== count event_name # count / runtime 598,995,035,942 cpu-cycles # 1.800861 GHz 81,195,620,851 raw-stall-frontend # 244.112 M/sec 347,754,466,597 iTLB-loads # 1.046 G/sec 2,970,248,900 iTLB-load-misses # 0.854122% miss rate Total test time: 332.854998 seconds. 2MB Pages: ========== count event_name # count / runtime 592,872,663,047 cpu-cycles # 1.800358 GHz 76,485,624,143 raw-stall-frontend # 232.261 M/sec 350,478,413,710 iTLB-loads # 1.064 G/sec 803,233,322 iTLB-load-misses # 0.229182% miss rate Total test time: 329.826087 seconds A check of /proc/$(pidof dex2oat64)/smaps shows THPs in use: /apex/com.android.art/lib64/libart.so FilePmdMapped: 4096 kB /apex/com.android.art/lib64/libart-compiler.so FilePmdMapped: 2048 kB Link: https://lkml.kernel.org/r/20210406000930.3455850-1-cfijalkovich@google.com Signed-off-by: Collin Fijalkovich <cfijalkovich@google.com> Acked-by: Hugh Dickins <hughd@google.com> Reviewed-by: William Kucharski <william.kucharski@oracle.com> Acked-by: Song Liu <song@kernel.org> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Hridya Valsaraju <hridya@google.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Tim Murray <timmurray@google.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-01 04:51:32 +03:00
if (f->f_mode & FMODE_WRITE) {
/*
* Paired with smp_mb() in collapse_file() to ensure nr_thps
* is up to date and the update to i_writecount by
* get_write_access() is visible. Ensures subsequent insertion
* of THPs into the page cache will fail.
*/
smp_mb();
mm, thp: lock filemap when truncating page cache Patch series "fix two bugs for file THP". This patch (of 2): Transparent huge page has supported read-only non-shmem files. The file- backed THP is collapsed by khugepaged and truncated when written (for shared libraries). However, there is a race when multiple writers truncate the same page cache concurrently. In that case, subpage(s) of file THP can be revealed by find_get_entry in truncate_inode_pages_range, which will trigger PageTail BUG_ON in truncate_inode_page, as follows: page:000000009e420ff2 refcount:1 mapcount:0 mapping:0000000000000000 index:0x7ff pfn:0x50c3ff head:0000000075ff816d order:9 compound_mapcount:0 compound_pincount:0 flags: 0x37fffe0000010815(locked|uptodate|lru|arch_1|head) raw: 37fffe0000000000 fffffe0013108001 dead000000000122 dead000000000400 raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000 head: 37fffe0000010815 fffffe001066bd48 ffff000404183c20 0000000000000000 head: 0000000000000600 0000000000000000 00000001ffffffff ffff000c0345a000 page dumped because: VM_BUG_ON_PAGE(PageTail(page)) ------------[ cut here ]------------ kernel BUG at mm/truncate.c:213! Internal error: Oops - BUG: 0 [#1] SMP Modules linked in: xfs(E) libcrc32c(E) rfkill(E) ... CPU: 14 PID: 11394 Comm: check_madvise_d Kdump: ... Hardware name: ECS, BIOS 0.0.0 02/06/2015 pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) Call trace: truncate_inode_page+0x64/0x70 truncate_inode_pages_range+0x550/0x7e4 truncate_pagecache+0x58/0x80 do_dentry_open+0x1e4/0x3c0 vfs_open+0x38/0x44 do_open+0x1f0/0x310 path_openat+0x114/0x1dc do_filp_open+0x84/0x134 do_sys_openat2+0xbc/0x164 __arm64_sys_openat+0x74/0xc0 el0_svc_common.constprop.0+0x88/0x220 do_el0_svc+0x30/0xa0 el0_svc+0x20/0x30 el0_sync_handler+0x1a4/0x1b0 el0_sync+0x180/0x1c0 Code: aa0103e0 900061e1 910ec021 9400d300 (d4210000) This patch mainly to lock filemap when one enter truncate_pagecache(), avoiding truncating the same page cache concurrently. Link: https://lkml.kernel.org/r/20211025092134.18562-1-rongwei.wang@linux.alibaba.com Link: https://lkml.kernel.org/r/20211025092134.18562-2-rongwei.wang@linux.alibaba.com Fixes: eb6ecbed0aa2 ("mm, thp: relax the VM_DENYWRITE constraint on file-backed THPs") Signed-off-by: Xu Yu <xuyu@linux.alibaba.com> Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com> Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org> Tested-by: Song Liu <song@kernel.org> Cc: Collin Fijalkovich <cfijalkovich@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: William Kucharski <william.kucharski@oracle.com> Cc: Yang Shi <shy828301@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-11-05 23:43:41 +03:00
if (filemap_nr_thps(inode->i_mapping)) {
struct address_space *mapping = inode->i_mapping;
mm, thp: lock filemap when truncating page cache Patch series "fix two bugs for file THP". This patch (of 2): Transparent huge page has supported read-only non-shmem files. The file- backed THP is collapsed by khugepaged and truncated when written (for shared libraries). However, there is a race when multiple writers truncate the same page cache concurrently. In that case, subpage(s) of file THP can be revealed by find_get_entry in truncate_inode_pages_range, which will trigger PageTail BUG_ON in truncate_inode_page, as follows: page:000000009e420ff2 refcount:1 mapcount:0 mapping:0000000000000000 index:0x7ff pfn:0x50c3ff head:0000000075ff816d order:9 compound_mapcount:0 compound_pincount:0 flags: 0x37fffe0000010815(locked|uptodate|lru|arch_1|head) raw: 37fffe0000000000 fffffe0013108001 dead000000000122 dead000000000400 raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000 head: 37fffe0000010815 fffffe001066bd48 ffff000404183c20 0000000000000000 head: 0000000000000600 0000000000000000 00000001ffffffff ffff000c0345a000 page dumped because: VM_BUG_ON_PAGE(PageTail(page)) ------------[ cut here ]------------ kernel BUG at mm/truncate.c:213! Internal error: Oops - BUG: 0 [#1] SMP Modules linked in: xfs(E) libcrc32c(E) rfkill(E) ... CPU: 14 PID: 11394 Comm: check_madvise_d Kdump: ... Hardware name: ECS, BIOS 0.0.0 02/06/2015 pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) Call trace: truncate_inode_page+0x64/0x70 truncate_inode_pages_range+0x550/0x7e4 truncate_pagecache+0x58/0x80 do_dentry_open+0x1e4/0x3c0 vfs_open+0x38/0x44 do_open+0x1f0/0x310 path_openat+0x114/0x1dc do_filp_open+0x84/0x134 do_sys_openat2+0xbc/0x164 __arm64_sys_openat+0x74/0xc0 el0_svc_common.constprop.0+0x88/0x220 do_el0_svc+0x30/0xa0 el0_svc+0x20/0x30 el0_sync_handler+0x1a4/0x1b0 el0_sync+0x180/0x1c0 Code: aa0103e0 900061e1 910ec021 9400d300 (d4210000) This patch mainly to lock filemap when one enter truncate_pagecache(), avoiding truncating the same page cache concurrently. Link: https://lkml.kernel.org/r/20211025092134.18562-1-rongwei.wang@linux.alibaba.com Link: https://lkml.kernel.org/r/20211025092134.18562-2-rongwei.wang@linux.alibaba.com Fixes: eb6ecbed0aa2 ("mm, thp: relax the VM_DENYWRITE constraint on file-backed THPs") Signed-off-by: Xu Yu <xuyu@linux.alibaba.com> Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com> Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org> Tested-by: Song Liu <song@kernel.org> Cc: Collin Fijalkovich <cfijalkovich@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: William Kucharski <william.kucharski@oracle.com> Cc: Yang Shi <shy828301@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-11-05 23:43:41 +03:00
filemap_invalidate_lock(inode->i_mapping);
/*
* unmap_mapping_range just need to be called once
* here, because the private pages is not need to be
* unmapped mapping (e.g. data segment of dynamic
* shared libraries here).
*/
unmap_mapping_range(mapping, 0, 0, 0);
truncate_inode_pages(mapping, 0);
mm, thp: lock filemap when truncating page cache Patch series "fix two bugs for file THP". This patch (of 2): Transparent huge page has supported read-only non-shmem files. The file- backed THP is collapsed by khugepaged and truncated when written (for shared libraries). However, there is a race when multiple writers truncate the same page cache concurrently. In that case, subpage(s) of file THP can be revealed by find_get_entry in truncate_inode_pages_range, which will trigger PageTail BUG_ON in truncate_inode_page, as follows: page:000000009e420ff2 refcount:1 mapcount:0 mapping:0000000000000000 index:0x7ff pfn:0x50c3ff head:0000000075ff816d order:9 compound_mapcount:0 compound_pincount:0 flags: 0x37fffe0000010815(locked|uptodate|lru|arch_1|head) raw: 37fffe0000000000 fffffe0013108001 dead000000000122 dead000000000400 raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000 head: 37fffe0000010815 fffffe001066bd48 ffff000404183c20 0000000000000000 head: 0000000000000600 0000000000000000 00000001ffffffff ffff000c0345a000 page dumped because: VM_BUG_ON_PAGE(PageTail(page)) ------------[ cut here ]------------ kernel BUG at mm/truncate.c:213! Internal error: Oops - BUG: 0 [#1] SMP Modules linked in: xfs(E) libcrc32c(E) rfkill(E) ... CPU: 14 PID: 11394 Comm: check_madvise_d Kdump: ... Hardware name: ECS, BIOS 0.0.0 02/06/2015 pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) Call trace: truncate_inode_page+0x64/0x70 truncate_inode_pages_range+0x550/0x7e4 truncate_pagecache+0x58/0x80 do_dentry_open+0x1e4/0x3c0 vfs_open+0x38/0x44 do_open+0x1f0/0x310 path_openat+0x114/0x1dc do_filp_open+0x84/0x134 do_sys_openat2+0xbc/0x164 __arm64_sys_openat+0x74/0xc0 el0_svc_common.constprop.0+0x88/0x220 do_el0_svc+0x30/0xa0 el0_svc+0x20/0x30 el0_sync_handler+0x1a4/0x1b0 el0_sync+0x180/0x1c0 Code: aa0103e0 900061e1 910ec021 9400d300 (d4210000) This patch mainly to lock filemap when one enter truncate_pagecache(), avoiding truncating the same page cache concurrently. Link: https://lkml.kernel.org/r/20211025092134.18562-1-rongwei.wang@linux.alibaba.com Link: https://lkml.kernel.org/r/20211025092134.18562-2-rongwei.wang@linux.alibaba.com Fixes: eb6ecbed0aa2 ("mm, thp: relax the VM_DENYWRITE constraint on file-backed THPs") Signed-off-by: Xu Yu <xuyu@linux.alibaba.com> Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com> Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org> Tested-by: Song Liu <song@kernel.org> Cc: Collin Fijalkovich <cfijalkovich@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: William Kucharski <william.kucharski@oracle.com> Cc: Yang Shi <shy828301@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-11-05 23:43:41 +03:00
filemap_invalidate_unlock(inode->i_mapping);
}
mm, thp: relax the VM_DENYWRITE constraint on file-backed THPs Transparent huge pages are supported for read-only non-shmem files, but are only used for vmas with VM_DENYWRITE. This condition ensures that file THPs are protected from writes while an application is running (ETXTBSY). Any existing file THPs are then dropped from the page cache when a file is opened for write in do_dentry_open(). Since sys_mmap ignores MAP_DENYWRITE, this constrains the use of file THPs to vmas produced by execve(). Systems that make heavy use of shared libraries (e.g. Android) are unable to apply VM_DENYWRITE through the dynamic linker, preventing them from benefiting from the resultant reduced contention on the TLB. This patch reduces the constraint on file THPs allowing use with any executable mapping from a file not opened for write (see inode_is_open_for_write()). It also introduces additional conditions to ensure that files opened for write will never be backed by file THPs. Restricting the use of THPs to executable mappings eliminates the risk that a read-only file later opened for write would encounter significant latencies due to page cache truncation. The ld linker flag '-z max-page-size=(hugepage size)' can be used to produce executables with the necessary layout. The dynamic linker must map these file's segments at a hugepage size aligned vma for the mapping to be backed with THPs. Comparison of the performance characteristics of 4KB and 2MB-backed libraries follows; the Android dex2oat tool was used to AOT compile an example application on a single ARM core. 4KB Pages: ========== count event_name # count / runtime 598,995,035,942 cpu-cycles # 1.800861 GHz 81,195,620,851 raw-stall-frontend # 244.112 M/sec 347,754,466,597 iTLB-loads # 1.046 G/sec 2,970,248,900 iTLB-load-misses # 0.854122% miss rate Total test time: 332.854998 seconds. 2MB Pages: ========== count event_name # count / runtime 592,872,663,047 cpu-cycles # 1.800358 GHz 76,485,624,143 raw-stall-frontend # 232.261 M/sec 350,478,413,710 iTLB-loads # 1.064 G/sec 803,233,322 iTLB-load-misses # 0.229182% miss rate Total test time: 329.826087 seconds A check of /proc/$(pidof dex2oat64)/smaps shows THPs in use: /apex/com.android.art/lib64/libart.so FilePmdMapped: 4096 kB /apex/com.android.art/lib64/libart-compiler.so FilePmdMapped: 2048 kB Link: https://lkml.kernel.org/r/20210406000930.3455850-1-cfijalkovich@google.com Signed-off-by: Collin Fijalkovich <cfijalkovich@google.com> Acked-by: Hugh Dickins <hughd@google.com> Reviewed-by: William Kucharski <william.kucharski@oracle.com> Acked-by: Song Liu <song@kernel.org> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Hridya Valsaraju <hridya@google.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Tim Murray <timmurray@google.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-01 04:51:32 +03:00
}
/*
* Once we return a file with FMODE_OPENED, __fput() will call
* fsnotify_close(), so we need fsnotify_open() here for symmetry.
*/
fsnotify_open(f);
return 0;
cleanup_all:
if (WARN_ON_ONCE(error > 0))
error = -EINVAL;
fops_put(f->f_op);
put_file_access(f);
cleanup_file:
path_put(&f->f_path);
f->f_path.mnt = NULL;
f->f_path.dentry = NULL;
f->f_inode = NULL;
return error;
}
/**
* finish_open - finish opening a file
* @file: file pointer
* @dentry: pointer to dentry
* @open: open callback
*
* This can be used to finish opening a file passed to i_op->atomic_open().
*
* If the open callback is set to NULL, then the standard f_op->open()
* filesystem callback is substituted.
*
* NB: the dentry reference is _not_ consumed. If, for example, the dentry is
* the return value of d_splice_alias(), then the caller needs to perform dput()
* on it after finish_open().
*
* Returns zero on success or -errno if the open failed.
*/
int finish_open(struct file *file, struct dentry *dentry,
int (*open)(struct inode *, struct file *))
{
BUG_ON(file->f_mode & FMODE_OPENED); /* once it's opened, it's opened */
file->f_path.dentry = dentry;
return do_dentry_open(file, d_backing_inode(dentry), open);
}
EXPORT_SYMBOL(finish_open);
/**
* finish_no_open - finish ->atomic_open() without opening the file
*
* @file: file pointer
* @dentry: dentry or NULL (as returned from ->lookup())
*
* This can be used to set the result of a successful lookup in ->atomic_open().
*
* NB: unlike finish_open() this function does consume the dentry reference and
* the caller need not dput() it.
*
* Returns "0" which must be the return value of ->atomic_open() after having
* called this function.
*/
int finish_no_open(struct file *file, struct dentry *dentry)
{
file->f_path.dentry = dentry;
return 0;
}
EXPORT_SYMBOL(finish_no_open);
char *file_path(struct file *filp, char *buf, int buflen)
{
return d_path(&filp->f_path, buf, buflen);
}
EXPORT_SYMBOL(file_path);
overlayfs: Make f_path always point to the overlay and f_inode to the underlay Make file->f_path always point to the overlay dentry so that the path in /proc/pid/fd is correct and to ensure that label-based LSMs have access to the overlay as well as the underlay (path-based LSMs probably don't need it). Using my union testsuite to set things up, before the patch I see: [root@andromeda union-testsuite]# bash 5</mnt/a/foo107 [root@andromeda union-testsuite]# ls -l /proc/$$/fd/ ... lr-x------. 1 root root 64 Jun 5 14:38 5 -> /a/foo107 [root@andromeda union-testsuite]# stat /mnt/a/foo107 ... Device: 23h/35d Inode: 13381 Links: 1 ... [root@andromeda union-testsuite]# stat -L /proc/$$/fd/5 ... Device: 23h/35d Inode: 13381 Links: 1 ... After the patch: [root@andromeda union-testsuite]# bash 5</mnt/a/foo107 [root@andromeda union-testsuite]# ls -l /proc/$$/fd/ ... lr-x------. 1 root root 64 Jun 5 14:22 5 -> /mnt/a/foo107 [root@andromeda union-testsuite]# stat /mnt/a/foo107 ... Device: 23h/35d Inode: 40346 Links: 1 ... [root@andromeda union-testsuite]# stat -L /proc/$$/fd/5 ... Device: 23h/35d Inode: 40346 Links: 1 ... Note the change in where /proc/$$/fd/5 points to in the ls command. It was pointing to /a/foo107 (which doesn't exist) and now points to /mnt/a/foo107 (which is correct). The inode accessed, however, is the lower layer. The union layer is on device 25h/37d and the upper layer on 24h/36d. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2015-06-18 16:32:31 +03:00
/**
* vfs_open - open the file at the given path
* @path: path to open
* @file: newly allocated file with f_flag initialized
*/
int vfs_open(const struct path *path, struct file *file)
overlayfs: Make f_path always point to the overlay and f_inode to the underlay Make file->f_path always point to the overlay dentry so that the path in /proc/pid/fd is correct and to ensure that label-based LSMs have access to the overlay as well as the underlay (path-based LSMs probably don't need it). Using my union testsuite to set things up, before the patch I see: [root@andromeda union-testsuite]# bash 5</mnt/a/foo107 [root@andromeda union-testsuite]# ls -l /proc/$$/fd/ ... lr-x------. 1 root root 64 Jun 5 14:38 5 -> /a/foo107 [root@andromeda union-testsuite]# stat /mnt/a/foo107 ... Device: 23h/35d Inode: 13381 Links: 1 ... [root@andromeda union-testsuite]# stat -L /proc/$$/fd/5 ... Device: 23h/35d Inode: 13381 Links: 1 ... After the patch: [root@andromeda union-testsuite]# bash 5</mnt/a/foo107 [root@andromeda union-testsuite]# ls -l /proc/$$/fd/ ... lr-x------. 1 root root 64 Jun 5 14:22 5 -> /mnt/a/foo107 [root@andromeda union-testsuite]# stat /mnt/a/foo107 ... Device: 23h/35d Inode: 40346 Links: 1 ... [root@andromeda union-testsuite]# stat -L /proc/$$/fd/5 ... Device: 23h/35d Inode: 40346 Links: 1 ... Note the change in where /proc/$$/fd/5 points to in the ls command. It was pointing to /a/foo107 (which doesn't exist) and now points to /mnt/a/foo107 (which is correct). The inode accessed, however, is the lower layer. The union layer is on device 25h/37d and the upper layer on 24h/36d. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2015-06-18 16:32:31 +03:00
{
file->f_path = *path;
return do_dentry_open(file, d_backing_inode(path->dentry), NULL);
overlayfs: Make f_path always point to the overlay and f_inode to the underlay Make file->f_path always point to the overlay dentry so that the path in /proc/pid/fd is correct and to ensure that label-based LSMs have access to the overlay as well as the underlay (path-based LSMs probably don't need it). Using my union testsuite to set things up, before the patch I see: [root@andromeda union-testsuite]# bash 5</mnt/a/foo107 [root@andromeda union-testsuite]# ls -l /proc/$$/fd/ ... lr-x------. 1 root root 64 Jun 5 14:38 5 -> /a/foo107 [root@andromeda union-testsuite]# stat /mnt/a/foo107 ... Device: 23h/35d Inode: 13381 Links: 1 ... [root@andromeda union-testsuite]# stat -L /proc/$$/fd/5 ... Device: 23h/35d Inode: 13381 Links: 1 ... After the patch: [root@andromeda union-testsuite]# bash 5</mnt/a/foo107 [root@andromeda union-testsuite]# ls -l /proc/$$/fd/ ... lr-x------. 1 root root 64 Jun 5 14:22 5 -> /mnt/a/foo107 [root@andromeda union-testsuite]# stat /mnt/a/foo107 ... Device: 23h/35d Inode: 40346 Links: 1 ... [root@andromeda union-testsuite]# stat -L /proc/$$/fd/5 ... Device: 23h/35d Inode: 40346 Links: 1 ... Note the change in where /proc/$$/fd/5 points to in the ls command. It was pointing to /a/foo107 (which doesn't exist) and now points to /mnt/a/foo107 (which is correct). The inode accessed, however, is the lower layer. The union layer is on device 25h/37d and the upper layer on 24h/36d. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2015-06-18 16:32:31 +03:00
}
struct file *dentry_open(const struct path *path, int flags,
const struct cred *cred)
{
int error;
struct file *f;
validate_creds(cred);
/* We must always pass in a valid mount pointer. */
BUG_ON(!path->mnt);
f = alloc_empty_file(flags, cred);
if (!IS_ERR(f)) {
error = vfs_open(path, f);
if (error) {
fput(f);
f = ERR_PTR(error);
}
}
return f;
}
EXPORT_SYMBOL(dentry_open);
/**
* dentry_create - Create and open a file
* @path: path to create
* @flags: O_ flags
* @mode: mode bits for new file
* @cred: credentials to use
*
* Caller must hold the parent directory's lock, and have prepared
* a negative dentry, placed in @path->dentry, for the new file.
*
* Caller sets @path->mnt to the vfsmount of the filesystem where
* the new file is to be created. The parent directory and the
* negative dentry must reside on the same filesystem instance.
*
* On success, returns a "struct file *". Otherwise a ERR_PTR
* is returned.
*/
struct file *dentry_create(const struct path *path, int flags, umode_t mode,
const struct cred *cred)
{
struct file *f;
int error;
validate_creds(cred);
f = alloc_empty_file(flags, cred);
if (IS_ERR(f))
return f;
error = vfs_create(mnt_idmap(path->mnt),
d_inode(path->dentry->d_parent),
path->dentry, mode, true);
if (!error)
error = vfs_open(path, f);
if (unlikely(error)) {
fput(f);
return ERR_PTR(error);
}
return f;
}
EXPORT_SYMBOL(dentry_create);
/**
* kernel_file_open - open a file for kernel internal use
* @path: path of the file to open
* @flags: open flags
* @inode: the inode
* @cred: credentials for open
*
* Open a file for use by in-kernel consumers. The file is not accounted
* against nr_files and must not be installed into the file descriptor
* table.
*
* Return: Opened file on success, an error pointer on failure.
*/
struct file *kernel_file_open(const struct path *path, int flags,
struct inode *inode, const struct cred *cred)
{
struct file *f;
int error;
f = alloc_empty_file_noaccount(flags, cred);
if (IS_ERR(f))
return f;
f->f_path = *path;
error = do_dentry_open(f, inode, NULL);
if (error) {
fput(f);
f = ERR_PTR(error);
}
return f;
}
EXPORT_SYMBOL_GPL(kernel_file_open);
/**
* backing_file_open - open a backing file for kernel internal use
* @user_path: path that the user reuqested to open
* @flags: open flags
* @real_path: path of the backing file
* @cred: credentials for open
*
* Open a backing file for a stackable filesystem (e.g., overlayfs).
* @user_path may be on the stackable filesystem and @real_path on the
* underlying filesystem. In this case, we want to be able to return the
* @user_path of the stackable filesystem. This is done by embedding the
* returned file into a container structure that also stores the stacked
* file's path, which can be retrieved using backing_file_user_path().
*/
struct file *backing_file_open(const struct path *user_path, int flags,
const struct path *real_path,
const struct cred *cred)
{
struct file *f;
int error;
f = alloc_empty_backing_file(flags, cred);
if (IS_ERR(f))
return f;
path_get(user_path);
*backing_file_user_path(f) = *user_path;
f->f_path = *real_path;
error = do_dentry_open(f, d_inode(real_path->dentry), NULL);
if (error) {
fput(f);
f = ERR_PTR(error);
}
return f;
}
EXPORT_SYMBOL_GPL(backing_file_open);
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
#define WILL_CREATE(flags) (flags & (O_CREAT | __O_TMPFILE))
#define O_PATH_FLAGS (O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC)
inline struct open_how build_open_how(int flags, umode_t mode)
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
{
struct open_how how = {
.flags = flags & VALID_OPEN_FLAGS,
.mode = mode & S_IALLUGO,
};
/* O_PATH beats everything else. */
if (how.flags & O_PATH)
how.flags &= O_PATH_FLAGS;
/* Modes should only be set for create-like flags. */
if (!WILL_CREATE(how.flags))
how.mode = 0;
return how;
}
inline int build_open_flags(const struct open_how *how, struct open_flags *op)
{
open: don't silently ignore unknown O-flags in openat2() The new openat2() syscall verifies that no unknown O-flag values are set and returns an error to userspace if they are while the older open syscalls like open() and openat() simply ignore unknown flag values: #define O_FLAG_CURRENTLY_INVALID (1 << 31) struct open_how how = { .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID, .resolve = 0, }; /* fails */ fd = openat2(-EBADF, "/dev/null", &how, sizeof(how)); /* succeeds */ fd = openat(-EBADF, "/dev/null", O_RDONLY | O_FLAG_CURRENTLY_INVALID); However, openat2() silently truncates the upper 32 bits meaning: #define O_FLAG_CURRENTLY_INVALID_LOWER32 (1 << 31) #define O_FLAG_CURRENTLY_INVALID_UPPER32 (1 << 40) struct open_how how_lowe32 = { .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID_LOWER32, }; struct open_how how_upper32 = { .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID_UPPER32, }; /* fails */ fd = openat2(-EBADF, "/dev/null", &how_lower32, sizeof(how_lower32)); /* succeeds */ fd = openat2(-EBADF, "/dev/null", &how_upper32, sizeof(how_upper32)); Fix this by preventing the immediate truncation in build_open_flags(). There's a snafu here though stripping FMODE_* directly from flags would cause the upper 32 bits to be truncated as well due to integer promotion rules since FMODE_* is unsigned int, O_* are signed ints (yuck). In addition, struct open_flags currently defines flags to be 32 bit which is reasonable. If we simply were to bump it to 64 bit we would need to change a lot of code preemptively which doesn't seem worth it. So simply add a compile-time check verifying that all currently known O_* flags are within the 32 bit range and fail to build if they aren't anymore. This change shouldn't regress old open syscalls since they silently truncate any unknown values anyway. It is a tiny semantic change for openat2() but it is very unlikely people pass ing > 32 bit unknown flags and the syscall is relatively new too. Link: https://lore.kernel.org/r/20210528092417.3942079-3-brauner@kernel.org Cc: Christoph Hellwig <hch@lst.de> Cc: Aleksa Sarai <cyphar@cyphar.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Reported-by: Richard Guy Briggs <rgb@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Aleksa Sarai <cyphar@cyphar.com> Reviewed-by: Richard Guy Briggs <rgb@redhat.com> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-05-28 12:24:16 +03:00
u64 flags = how->flags;
u64 strip = __FMODE_NONOTIFY | O_CLOEXEC;
int lookup_flags = 0;
int acc_mode = ACC_MODE(flags);
open: don't silently ignore unknown O-flags in openat2() The new openat2() syscall verifies that no unknown O-flag values are set and returns an error to userspace if they are while the older open syscalls like open() and openat() simply ignore unknown flag values: #define O_FLAG_CURRENTLY_INVALID (1 << 31) struct open_how how = { .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID, .resolve = 0, }; /* fails */ fd = openat2(-EBADF, "/dev/null", &how, sizeof(how)); /* succeeds */ fd = openat(-EBADF, "/dev/null", O_RDONLY | O_FLAG_CURRENTLY_INVALID); However, openat2() silently truncates the upper 32 bits meaning: #define O_FLAG_CURRENTLY_INVALID_LOWER32 (1 << 31) #define O_FLAG_CURRENTLY_INVALID_UPPER32 (1 << 40) struct open_how how_lowe32 = { .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID_LOWER32, }; struct open_how how_upper32 = { .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID_UPPER32, }; /* fails */ fd = openat2(-EBADF, "/dev/null", &how_lower32, sizeof(how_lower32)); /* succeeds */ fd = openat2(-EBADF, "/dev/null", &how_upper32, sizeof(how_upper32)); Fix this by preventing the immediate truncation in build_open_flags(). There's a snafu here though stripping FMODE_* directly from flags would cause the upper 32 bits to be truncated as well due to integer promotion rules since FMODE_* is unsigned int, O_* are signed ints (yuck). In addition, struct open_flags currently defines flags to be 32 bit which is reasonable. If we simply were to bump it to 64 bit we would need to change a lot of code preemptively which doesn't seem worth it. So simply add a compile-time check verifying that all currently known O_* flags are within the 32 bit range and fail to build if they aren't anymore. This change shouldn't regress old open syscalls since they silently truncate any unknown values anyway. It is a tiny semantic change for openat2() but it is very unlikely people pass ing > 32 bit unknown flags and the syscall is relatively new too. Link: https://lore.kernel.org/r/20210528092417.3942079-3-brauner@kernel.org Cc: Christoph Hellwig <hch@lst.de> Cc: Aleksa Sarai <cyphar@cyphar.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Reported-by: Richard Guy Briggs <rgb@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Aleksa Sarai <cyphar@cyphar.com> Reviewed-by: Richard Guy Briggs <rgb@redhat.com> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-05-28 12:24:16 +03:00
BUILD_BUG_ON_MSG(upper_32_bits(VALID_OPEN_FLAGS),
"struct open_flags doesn't yet handle flags > 32 bits");
/*
* Strip flags that either shouldn't be set by userspace like
* FMODE_NONOTIFY or that aren't relevant in determining struct
* open_flags like O_CLOEXEC.
*/
flags &= ~strip;
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
/*
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
* Older syscalls implicitly clear all of the invalid flags or argument
* values before calling build_open_flags(), but openat2(2) checks all
* of its arguments.
*/
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
if (flags & ~VALID_OPEN_FLAGS)
return -EINVAL;
if (how->resolve & ~VALID_RESOLVE_FLAGS)
return -EINVAL;
/* Scoping flags are mutually exclusive. */
if ((how->resolve & RESOLVE_BENEATH) && (how->resolve & RESOLVE_IN_ROOT))
return -EINVAL;
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
/* Deal with the mode. */
if (WILL_CREATE(flags)) {
if (how->mode & ~S_IALLUGO)
return -EINVAL;
op->mode = how->mode | S_IFREG;
} else {
if (how->mode != 0)
return -EINVAL;
op->mode = 0;
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
}
/*
open: return EINVAL for O_DIRECTORY | O_CREAT After a couple of years and multiple LTS releases we received a report that the behavior of O_DIRECTORY | O_CREAT changed starting with v5.7. On kernels prior to v5.7 combinations of O_DIRECTORY, O_CREAT, O_EXCL had the following semantics: (1) open("/tmp/d", O_DIRECTORY | O_CREAT) * d doesn't exist: create regular file * d exists and is a regular file: ENOTDIR * d exists and is a directory: EISDIR (2) open("/tmp/d", O_DIRECTORY | O_CREAT | O_EXCL) * d doesn't exist: create regular file * d exists and is a regular file: EEXIST * d exists and is a directory: EEXIST (3) open("/tmp/d", O_DIRECTORY | O_EXCL) * d doesn't exist: ENOENT * d exists and is a regular file: ENOTDIR * d exists and is a directory: open directory On kernels since to v5.7 combinations of O_DIRECTORY, O_CREAT, O_EXCL have the following semantics: (1) open("/tmp/d", O_DIRECTORY | O_CREAT) * d doesn't exist: ENOTDIR (create regular file) * d exists and is a regular file: ENOTDIR * d exists and is a directory: EISDIR (2) open("/tmp/d", O_DIRECTORY | O_CREAT | O_EXCL) * d doesn't exist: ENOTDIR (create regular file) * d exists and is a regular file: EEXIST * d exists and is a directory: EEXIST (3) open("/tmp/d", O_DIRECTORY | O_EXCL) * d doesn't exist: ENOENT * d exists and is a regular file: ENOTDIR * d exists and is a directory: open directory This is a fairly substantial semantic change that userspace didn't notice until Pedro took the time to deliberately figure out corner cases. Since no one noticed this breakage we can somewhat safely assume that O_DIRECTORY | O_CREAT combinations are likely unused. The v5.7 breakage is especially weird because while ENOTDIR is returned indicating failure a regular file is actually created. This doesn't make a lot of sense. Time was spent finding potential users of this combination. Searching on codesearch.debian.net showed that codebases often express semantical expectations about O_DIRECTORY | O_CREAT which are completely contrary to what our code has done and currently does. The expectation often is that this particular combination would create and open a directory. This suggests users who tried to use that combination would stumble upon the counterintuitive behavior no matter if pre-v5.7 or post v5.7 and quickly realize neither semantics give them what they want. For some examples see the code examples in [1] to [3] and the discussion in [4]. There are various ways to address this issue. The lazy/simple option would be to restore the pre-v5.7 behavior and to just live with that bug forever. But since there's a real chance that the O_DIRECTORY | O_CREAT quirk isn't relied upon we should try to get away with murder(ing bad semantics) first. If we need to Frankenstein pre-v5.7 behavior later so be it. So let's simply return EINVAL categorically for O_DIRECTORY | O_CREAT combinations. In addition to cleaning up the old bug this also opens up the possiblity to make that flag combination do something more intuitive in the future. Starting with this commit the following semantics apply: (1) open("/tmp/d", O_DIRECTORY | O_CREAT) * d doesn't exist: EINVAL * d exists and is a regular file: EINVAL * d exists and is a directory: EINVAL (2) open("/tmp/d", O_DIRECTORY | O_CREAT | O_EXCL) * d doesn't exist: EINVAL * d exists and is a regular file: EINVAL * d exists and is a directory: EINVAL (3) open("/tmp/d", O_DIRECTORY | O_EXCL) * d doesn't exist: ENOENT * d exists and is a regular file: ENOTDIR * d exists and is a directory: open directory One additional note, O_TMPFILE is implemented as: #define __O_TMPFILE 020000000 #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY) #define O_TMPFILE_MASK (__O_TMPFILE | O_DIRECTORY | O_CREAT) For older kernels it was important to return an explicit error when O_TMPFILE wasn't supported. So O_TMPFILE requires that O_DIRECTORY is raised alongside __O_TMPFILE. It also enforced that O_CREAT wasn't specified. Since O_DIRECTORY | O_CREAT could be used to create a regular allowing that combination together with __O_TMPFILE would've meant that false positives were possible, i.e., that a regular file was created instead of a O_TMPFILE. This could've been used to trick userspace into thinking it operated on a O_TMPFILE when it wasn't. Now that we block O_DIRECTORY | O_CREAT completely the check for O_CREAT in the __O_TMPFILE branch via if ((flags & O_TMPFILE_MASK) != O_TMPFILE) can be dropped. Instead we can simply check verify that O_DIRECTORY is raised via if (!(flags & O_DIRECTORY)) and explain this in two comments. As Aleksa pointed out O_PATH is unaffected by this change since it always returned EINVAL if O_CREAT was specified - with or without O_DIRECTORY. Link: https://lore.kernel.org/lkml/20230320071442.172228-1-pedro.falcato@gmail.com Link: https://sources.debian.org/src/flatpak/1.14.4-1/subprojects/libglnx/glnx-dirfd.c/?hl=324#L324 [1] Link: https://sources.debian.org/src/flatpak-builder/1.2.3-1/subprojects/libglnx/glnx-shutil.c/?hl=251#L251 [2] Link: https://sources.debian.org/src/ostree/2022.7-2/libglnx/glnx-dirfd.c/?hl=324#L324 [3] Link: https://www.openwall.com/lists/oss-security/2014/11/26/14 [4] Reported-by: Pedro Falcato <pedro.falcato@gmail.com> Cc: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Christian Brauner <brauner@kernel.org>
2023-03-21 11:18:07 +03:00
* Block bugs where O_DIRECTORY | O_CREAT created regular files.
* Note, that blocking O_DIRECTORY | O_CREAT here also protects
* O_TMPFILE below which requires O_DIRECTORY being raised.
*/
open: return EINVAL for O_DIRECTORY | O_CREAT After a couple of years and multiple LTS releases we received a report that the behavior of O_DIRECTORY | O_CREAT changed starting with v5.7. On kernels prior to v5.7 combinations of O_DIRECTORY, O_CREAT, O_EXCL had the following semantics: (1) open("/tmp/d", O_DIRECTORY | O_CREAT) * d doesn't exist: create regular file * d exists and is a regular file: ENOTDIR * d exists and is a directory: EISDIR (2) open("/tmp/d", O_DIRECTORY | O_CREAT | O_EXCL) * d doesn't exist: create regular file * d exists and is a regular file: EEXIST * d exists and is a directory: EEXIST (3) open("/tmp/d", O_DIRECTORY | O_EXCL) * d doesn't exist: ENOENT * d exists and is a regular file: ENOTDIR * d exists and is a directory: open directory On kernels since to v5.7 combinations of O_DIRECTORY, O_CREAT, O_EXCL have the following semantics: (1) open("/tmp/d", O_DIRECTORY | O_CREAT) * d doesn't exist: ENOTDIR (create regular file) * d exists and is a regular file: ENOTDIR * d exists and is a directory: EISDIR (2) open("/tmp/d", O_DIRECTORY | O_CREAT | O_EXCL) * d doesn't exist: ENOTDIR (create regular file) * d exists and is a regular file: EEXIST * d exists and is a directory: EEXIST (3) open("/tmp/d", O_DIRECTORY | O_EXCL) * d doesn't exist: ENOENT * d exists and is a regular file: ENOTDIR * d exists and is a directory: open directory This is a fairly substantial semantic change that userspace didn't notice until Pedro took the time to deliberately figure out corner cases. Since no one noticed this breakage we can somewhat safely assume that O_DIRECTORY | O_CREAT combinations are likely unused. The v5.7 breakage is especially weird because while ENOTDIR is returned indicating failure a regular file is actually created. This doesn't make a lot of sense. Time was spent finding potential users of this combination. Searching on codesearch.debian.net showed that codebases often express semantical expectations about O_DIRECTORY | O_CREAT which are completely contrary to what our code has done and currently does. The expectation often is that this particular combination would create and open a directory. This suggests users who tried to use that combination would stumble upon the counterintuitive behavior no matter if pre-v5.7 or post v5.7 and quickly realize neither semantics give them what they want. For some examples see the code examples in [1] to [3] and the discussion in [4]. There are various ways to address this issue. The lazy/simple option would be to restore the pre-v5.7 behavior and to just live with that bug forever. But since there's a real chance that the O_DIRECTORY | O_CREAT quirk isn't relied upon we should try to get away with murder(ing bad semantics) first. If we need to Frankenstein pre-v5.7 behavior later so be it. So let's simply return EINVAL categorically for O_DIRECTORY | O_CREAT combinations. In addition to cleaning up the old bug this also opens up the possiblity to make that flag combination do something more intuitive in the future. Starting with this commit the following semantics apply: (1) open("/tmp/d", O_DIRECTORY | O_CREAT) * d doesn't exist: EINVAL * d exists and is a regular file: EINVAL * d exists and is a directory: EINVAL (2) open("/tmp/d", O_DIRECTORY | O_CREAT | O_EXCL) * d doesn't exist: EINVAL * d exists and is a regular file: EINVAL * d exists and is a directory: EINVAL (3) open("/tmp/d", O_DIRECTORY | O_EXCL) * d doesn't exist: ENOENT * d exists and is a regular file: ENOTDIR * d exists and is a directory: open directory One additional note, O_TMPFILE is implemented as: #define __O_TMPFILE 020000000 #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY) #define O_TMPFILE_MASK (__O_TMPFILE | O_DIRECTORY | O_CREAT) For older kernels it was important to return an explicit error when O_TMPFILE wasn't supported. So O_TMPFILE requires that O_DIRECTORY is raised alongside __O_TMPFILE. It also enforced that O_CREAT wasn't specified. Since O_DIRECTORY | O_CREAT could be used to create a regular allowing that combination together with __O_TMPFILE would've meant that false positives were possible, i.e., that a regular file was created instead of a O_TMPFILE. This could've been used to trick userspace into thinking it operated on a O_TMPFILE when it wasn't. Now that we block O_DIRECTORY | O_CREAT completely the check for O_CREAT in the __O_TMPFILE branch via if ((flags & O_TMPFILE_MASK) != O_TMPFILE) can be dropped. Instead we can simply check verify that O_DIRECTORY is raised via if (!(flags & O_DIRECTORY)) and explain this in two comments. As Aleksa pointed out O_PATH is unaffected by this change since it always returned EINVAL if O_CREAT was specified - with or without O_DIRECTORY. Link: https://lore.kernel.org/lkml/20230320071442.172228-1-pedro.falcato@gmail.com Link: https://sources.debian.org/src/flatpak/1.14.4-1/subprojects/libglnx/glnx-dirfd.c/?hl=324#L324 [1] Link: https://sources.debian.org/src/flatpak-builder/1.2.3-1/subprojects/libglnx/glnx-shutil.c/?hl=251#L251 [2] Link: https://sources.debian.org/src/ostree/2022.7-2/libglnx/glnx-dirfd.c/?hl=324#L324 [3] Link: https://www.openwall.com/lists/oss-security/2014/11/26/14 [4] Reported-by: Pedro Falcato <pedro.falcato@gmail.com> Cc: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Christian Brauner <brauner@kernel.org>
2023-03-21 11:18:07 +03:00
if ((flags & (O_DIRECTORY | O_CREAT)) == (O_DIRECTORY | O_CREAT))
return -EINVAL;
/* Now handle the creative implementation of O_TMPFILE. */
if (flags & __O_TMPFILE) {
open: return EINVAL for O_DIRECTORY | O_CREAT After a couple of years and multiple LTS releases we received a report that the behavior of O_DIRECTORY | O_CREAT changed starting with v5.7. On kernels prior to v5.7 combinations of O_DIRECTORY, O_CREAT, O_EXCL had the following semantics: (1) open("/tmp/d", O_DIRECTORY | O_CREAT) * d doesn't exist: create regular file * d exists and is a regular file: ENOTDIR * d exists and is a directory: EISDIR (2) open("/tmp/d", O_DIRECTORY | O_CREAT | O_EXCL) * d doesn't exist: create regular file * d exists and is a regular file: EEXIST * d exists and is a directory: EEXIST (3) open("/tmp/d", O_DIRECTORY | O_EXCL) * d doesn't exist: ENOENT * d exists and is a regular file: ENOTDIR * d exists and is a directory: open directory On kernels since to v5.7 combinations of O_DIRECTORY, O_CREAT, O_EXCL have the following semantics: (1) open("/tmp/d", O_DIRECTORY | O_CREAT) * d doesn't exist: ENOTDIR (create regular file) * d exists and is a regular file: ENOTDIR * d exists and is a directory: EISDIR (2) open("/tmp/d", O_DIRECTORY | O_CREAT | O_EXCL) * d doesn't exist: ENOTDIR (create regular file) * d exists and is a regular file: EEXIST * d exists and is a directory: EEXIST (3) open("/tmp/d", O_DIRECTORY | O_EXCL) * d doesn't exist: ENOENT * d exists and is a regular file: ENOTDIR * d exists and is a directory: open directory This is a fairly substantial semantic change that userspace didn't notice until Pedro took the time to deliberately figure out corner cases. Since no one noticed this breakage we can somewhat safely assume that O_DIRECTORY | O_CREAT combinations are likely unused. The v5.7 breakage is especially weird because while ENOTDIR is returned indicating failure a regular file is actually created. This doesn't make a lot of sense. Time was spent finding potential users of this combination. Searching on codesearch.debian.net showed that codebases often express semantical expectations about O_DIRECTORY | O_CREAT which are completely contrary to what our code has done and currently does. The expectation often is that this particular combination would create and open a directory. This suggests users who tried to use that combination would stumble upon the counterintuitive behavior no matter if pre-v5.7 or post v5.7 and quickly realize neither semantics give them what they want. For some examples see the code examples in [1] to [3] and the discussion in [4]. There are various ways to address this issue. The lazy/simple option would be to restore the pre-v5.7 behavior and to just live with that bug forever. But since there's a real chance that the O_DIRECTORY | O_CREAT quirk isn't relied upon we should try to get away with murder(ing bad semantics) first. If we need to Frankenstein pre-v5.7 behavior later so be it. So let's simply return EINVAL categorically for O_DIRECTORY | O_CREAT combinations. In addition to cleaning up the old bug this also opens up the possiblity to make that flag combination do something more intuitive in the future. Starting with this commit the following semantics apply: (1) open("/tmp/d", O_DIRECTORY | O_CREAT) * d doesn't exist: EINVAL * d exists and is a regular file: EINVAL * d exists and is a directory: EINVAL (2) open("/tmp/d", O_DIRECTORY | O_CREAT | O_EXCL) * d doesn't exist: EINVAL * d exists and is a regular file: EINVAL * d exists and is a directory: EINVAL (3) open("/tmp/d", O_DIRECTORY | O_EXCL) * d doesn't exist: ENOENT * d exists and is a regular file: ENOTDIR * d exists and is a directory: open directory One additional note, O_TMPFILE is implemented as: #define __O_TMPFILE 020000000 #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY) #define O_TMPFILE_MASK (__O_TMPFILE | O_DIRECTORY | O_CREAT) For older kernels it was important to return an explicit error when O_TMPFILE wasn't supported. So O_TMPFILE requires that O_DIRECTORY is raised alongside __O_TMPFILE. It also enforced that O_CREAT wasn't specified. Since O_DIRECTORY | O_CREAT could be used to create a regular allowing that combination together with __O_TMPFILE would've meant that false positives were possible, i.e., that a regular file was created instead of a O_TMPFILE. This could've been used to trick userspace into thinking it operated on a O_TMPFILE when it wasn't. Now that we block O_DIRECTORY | O_CREAT completely the check for O_CREAT in the __O_TMPFILE branch via if ((flags & O_TMPFILE_MASK) != O_TMPFILE) can be dropped. Instead we can simply check verify that O_DIRECTORY is raised via if (!(flags & O_DIRECTORY)) and explain this in two comments. As Aleksa pointed out O_PATH is unaffected by this change since it always returned EINVAL if O_CREAT was specified - with or without O_DIRECTORY. Link: https://lore.kernel.org/lkml/20230320071442.172228-1-pedro.falcato@gmail.com Link: https://sources.debian.org/src/flatpak/1.14.4-1/subprojects/libglnx/glnx-dirfd.c/?hl=324#L324 [1] Link: https://sources.debian.org/src/flatpak-builder/1.2.3-1/subprojects/libglnx/glnx-shutil.c/?hl=251#L251 [2] Link: https://sources.debian.org/src/ostree/2022.7-2/libglnx/glnx-dirfd.c/?hl=324#L324 [3] Link: https://www.openwall.com/lists/oss-security/2014/11/26/14 [4] Reported-by: Pedro Falcato <pedro.falcato@gmail.com> Cc: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Christian Brauner <brauner@kernel.org>
2023-03-21 11:18:07 +03:00
/*
* In order to ensure programs get explicit errors when trying
* to use O_TMPFILE on old kernels we enforce that O_DIRECTORY
* is raised alongside __O_TMPFILE.
*/
if (!(flags & O_DIRECTORY))
return -EINVAL;
if (!(acc_mode & MAY_WRITE))
return -EINVAL;
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
}
if (flags & O_PATH) {
/* O_PATH only permits certain other flags to be set. */
if (flags & ~O_PATH_FLAGS)
return -EINVAL;
2011-03-13 10:51:11 +03:00
acc_mode = 0;
}
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
/*
* O_SYNC is implemented as __O_SYNC|O_DSYNC. As many places only
* check for O_DSYNC if the need any syncing at all we enforce it's
* always set instead of having to deal with possibly weird behaviour
* for malicious applications setting only __O_SYNC.
*/
if (flags & __O_SYNC)
flags |= O_DSYNC;
2011-03-13 10:51:11 +03:00
op->open_flag = flags;
/* O_TRUNC implies we need access checks for write permissions */
if (flags & O_TRUNC)
acc_mode |= MAY_WRITE;
/* Allow the LSM permission hook to distinguish append
access from general write access. */
if (flags & O_APPEND)
acc_mode |= MAY_APPEND;
op->acc_mode = acc_mode;
2011-03-13 10:51:11 +03:00
op->intent = flags & O_PATH ? 0 : LOOKUP_OPEN;
if (flags & O_CREAT) {
op->intent |= LOOKUP_CREATE;
if (flags & O_EXCL) {
op->intent |= LOOKUP_EXCL;
flags |= O_NOFOLLOW;
}
}
if (flags & O_DIRECTORY)
lookup_flags |= LOOKUP_DIRECTORY;
if (!(flags & O_NOFOLLOW))
lookup_flags |= LOOKUP_FOLLOW;
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
if (how->resolve & RESOLVE_NO_XDEV)
lookup_flags |= LOOKUP_NO_XDEV;
if (how->resolve & RESOLVE_NO_MAGICLINKS)
lookup_flags |= LOOKUP_NO_MAGICLINKS;
if (how->resolve & RESOLVE_NO_SYMLINKS)
lookup_flags |= LOOKUP_NO_SYMLINKS;
if (how->resolve & RESOLVE_BENEATH)
lookup_flags |= LOOKUP_BENEATH;
if (how->resolve & RESOLVE_IN_ROOT)
lookup_flags |= LOOKUP_IN_ROOT;
if (how->resolve & RESOLVE_CACHED) {
/* Don't bother even trying for create/truncate/tmpfile open */
if (flags & (O_TRUNC | O_CREAT | __O_TMPFILE))
return -EAGAIN;
lookup_flags |= LOOKUP_CACHED;
}
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
op->lookup_flags = lookup_flags;
return 0;
}
/**
* file_open_name - open file and return file pointer
*
* @name: struct filename containing path to open
* @flags: open flags as per the open(2) second argument
* @mode: mode for the new file if O_CREAT is set, else ignored
*
* This is the helper to open a file from kernelspace if you really
* have to. But in generally you should not do this, so please move
* along, nothing to see here..
*/
struct file *file_open_name(struct filename *name, int flags, umode_t mode)
{
struct open_flags op;
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
struct open_how how = build_open_how(flags, mode);
int err = build_open_flags(&how, &op);
if (err)
return ERR_PTR(err);
return do_filp_open(AT_FDCWD, name, &op);
}
/**
* filp_open - open file and return file pointer
*
* @filename: path to open
* @flags: open flags as per the open(2) second argument
* @mode: mode for the new file if O_CREAT is set, else ignored
*
* This is the helper to open a file from kernelspace if you really
* have to. But in generally you should not do this, so please move
* along, nothing to see here..
*/
struct file *filp_open(const char *filename, int flags, umode_t mode)
{
struct filename *name = getname_kernel(filename);
struct file *file = ERR_CAST(name);
if (!IS_ERR(name)) {
file = file_open_name(name, flags, mode);
putname(name);
}
return file;
}
EXPORT_SYMBOL(filp_open);
struct file *file_open_root(const struct path *root,
2016-03-23 00:25:36 +03:00
const char *filename, int flags, umode_t mode)
{
struct open_flags op;
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
struct open_how how = build_open_how(flags, mode);
int err = build_open_flags(&how, &op);
if (err)
return ERR_PTR(err);
return do_file_open_root(root, filename, &op);
}
EXPORT_SYMBOL(file_open_root);
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
static long do_sys_openat2(int dfd, const char __user *filename,
struct open_how *how)
{
struct open_flags op;
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
int fd = build_open_flags(how, &op);
struct filename *tmp;
if (fd)
return fd;
tmp = getname(filename);
if (IS_ERR(tmp))
return PTR_ERR(tmp);
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
fd = get_unused_fd_flags(how->flags);
if (fd >= 0) {
struct file *f = do_filp_open(dfd, tmp, &op);
if (IS_ERR(f)) {
put_unused_fd(fd);
fd = PTR_ERR(f);
} else {
fd_install(fd, f);
}
}
putname(tmp);
return fd;
}
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)
{
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
struct open_how how = build_open_how(flags, mode);
return do_sys_openat2(dfd, filename, &how);
}
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, mode)
{
if (force_o_largefile())
flags |= O_LARGEFILE;
return do_sys_open(AT_FDCWD, filename, flags, mode);
}
SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags,
umode_t, mode)
[PATCH] vfs: *at functions: core Here is a series of patches which introduce in total 13 new system calls which take a file descriptor/filename pair instead of a single file name. These functions, openat etc, have been discussed on numerous occasions. They are needed to implement race-free filesystem traversal, they are necessary to implement a virtual per-thread current working directory (think multi-threaded backup software), etc. We have in glibc today implementations of the interfaces which use the /proc/self/fd magic. But this code is rather expensive. Here are some results (similar to what Jim Meyering posted before). The test creates a deep directory hierarchy on a tmpfs filesystem. Then rm -fr is used to remove all directories. Without syscall support I get this: real 0m31.921s user 0m0.688s sys 0m31.234s With syscall support the results are much better: real 0m20.699s user 0m0.536s sys 0m20.149s The interfaces are for obvious reasons currently not much used. But they'll be used. coreutils (and Jeff's posixutils) are already using them. Furthermore, code like ftw/fts in libc (maybe even glob) will also start using them. I expect a patch to make follow soon. Every program which is walking the filesystem tree will benefit. Signed-off-by: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@ftp.linux.org.uk> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-19 04:43:53 +03:00
{
if (force_o_largefile())
flags |= O_LARGEFILE;
return do_sys_open(dfd, filename, flags, mode);
[PATCH] vfs: *at functions: core Here is a series of patches which introduce in total 13 new system calls which take a file descriptor/filename pair instead of a single file name. These functions, openat etc, have been discussed on numerous occasions. They are needed to implement race-free filesystem traversal, they are necessary to implement a virtual per-thread current working directory (think multi-threaded backup software), etc. We have in glibc today implementations of the interfaces which use the /proc/self/fd magic. But this code is rather expensive. Here are some results (similar to what Jim Meyering posted before). The test creates a deep directory hierarchy on a tmpfs filesystem. Then rm -fr is used to remove all directories. Without syscall support I get this: real 0m31.921s user 0m0.688s sys 0m31.234s With syscall support the results are much better: real 0m20.699s user 0m0.536s sys 0m20.149s The interfaces are for obvious reasons currently not much used. But they'll be used. coreutils (and Jeff's posixutils) are already using them. Furthermore, code like ftw/fts in libc (maybe even glob) will also start using them. I expect a patch to make follow soon. Every program which is walking the filesystem tree will benefit. Signed-off-by: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@ftp.linux.org.uk> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-19 04:43:53 +03:00
}
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
SYSCALL_DEFINE4(openat2, int, dfd, const char __user *, filename,
struct open_how __user *, how, size_t, usize)
{
int err;
struct open_how tmp;
BUILD_BUG_ON(sizeof(struct open_how) < OPEN_HOW_SIZE_VER0);
BUILD_BUG_ON(sizeof(struct open_how) != OPEN_HOW_SIZE_LATEST);
if (unlikely(usize < OPEN_HOW_SIZE_VER0))
return -EINVAL;
err = copy_struct_from_user(&tmp, sizeof(tmp), how, usize);
if (err)
return err;
audit: add OPENAT2 record to list "how" info Since the openat2(2) syscall uses a struct open_how pointer to communicate its parameters they are not usefully recorded by the audit SYSCALL record's four existing arguments. Add a new audit record type OPENAT2 that reports the parameters in its third argument, struct open_how with fields oflag, mode and resolve. The new record in the context of an event would look like: time->Wed Mar 17 16:28:53 2021 type=PROCTITLE msg=audit(1616012933.531:184): proctitle= 73797363616C6C735F66696C652F6F70656E617432002F746D702F61756469742D 7465737473756974652D737641440066696C652D6F70656E617432 type=PATH msg=audit(1616012933.531:184): item=1 name="file-openat2" inode=29 dev=00:1f mode=0100600 ouid=0 ogid=0 rdev=00:00 obj=unconfined_u:object_r:user_tmp_t:s0 nametype=CREATE cap_fp=0 cap_fi=0 cap_fe=0 cap_fver=0 cap_frootid=0 type=PATH msg=audit(1616012933.531:184): item=0 name="/root/rgb/git/audit-testsuite/tests" inode=25 dev=00:1f mode=040700 ouid=0 ogid=0 rdev=00:00 obj=unconfined_u:object_r:user_tmp_t:s0 nametype=PARENT cap_fp=0 cap_fi=0 cap_fe=0 cap_fver=0 cap_frootid=0 type=CWD msg=audit(1616012933.531:184): cwd="/root/rgb/git/audit-testsuite/tests" type=OPENAT2 msg=audit(1616012933.531:184): oflag=0100302 mode=0600 resolve=0xa type=SYSCALL msg=audit(1616012933.531:184): arch=c000003e syscall=437 success=yes exit=4 a0=3 a1=7ffe315f1c53 a2=7ffe315f1550 a3=18 items=2 ppid=528 pid=540 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=1 comm="openat2" exe="/root/rgb/git/audit-testsuite/tests/syscalls_file/openat2" subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 key="testsuite-1616012933-bjAUcEPO" Link: https://lore.kernel.org/r/d23fbb89186754487850367224b060e26f9b7181.1621363275.git.rgb@redhat.com Signed-off-by: Richard Guy Briggs <rgb@redhat.com> Acked-by: Christian Brauner <christian.brauner@ubuntu.com> [PM: tweak subject, wrap example, move AUDIT_OPENAT2 to 1337] Signed-off-by: Paul Moore <paul@paul-moore.com>
2021-05-19 23:00:22 +03:00
audit_openat2_how(&tmp);
open: introduce openat2(2) syscall /* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1]. This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2). Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof. In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument. Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2). /* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ }; int openat2(int dfd, const char *pathname, struct open_how *how, size_t size); /* Description. */ The initial version of 'struct open_how' contains the following fields: flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2). mode The file mode for O_CREAT or O_TMPFILE. Must be set to zero if flags does not contain O_CREAT or O_TMPFILE. resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag). RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future. Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2). After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header. /* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios. In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace). /* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution). Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened. Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out). [1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs Suggested-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-18 15:07:59 +03:00
/* O_LARGEFILE is only allowed for non-O_PATH. */
if (!(tmp.flags & O_PATH) && force_o_largefile())
tmp.flags |= O_LARGEFILE;
return do_sys_openat2(dfd, filename, &tmp);
}
#ifdef CONFIG_COMPAT
/*
* Exactly like sys_open(), except that it doesn't set the
* O_LARGEFILE flag.
*/
COMPAT_SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, mode)
{
return do_sys_open(AT_FDCWD, filename, flags, mode);
}
/*
* Exactly like sys_openat(), except that it doesn't set the
* O_LARGEFILE flag.
*/
COMPAT_SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags, umode_t, mode)
{
return do_sys_open(dfd, filename, flags, mode);
}
#endif
#ifndef __alpha__
/*
* For backward compatibility? Maybe this should be moved
* into arch/i386 instead?
*/
SYSCALL_DEFINE2(creat, const char __user *, pathname, umode_t, mode)
{
int flags = O_CREAT | O_WRONLY | O_TRUNC;
if (force_o_largefile())
flags |= O_LARGEFILE;
return do_sys_open(AT_FDCWD, pathname, flags, mode);
}
#endif
/*
* "id" is the POSIX thread ID. We use the
* files pointer for this..
*/
static int filp_flush(struct file *filp, fl_owner_t id)
{
int retval = 0;
if (CHECK_DATA_CORRUPTION(file_count(filp) == 0,
"VFS: Close: file count is 0 (f_op=%ps)",
filp->f_op)) {
return 0;
}
if (filp->f_op->flush)
retval = filp->f_op->flush(filp, id);
2011-03-13 10:51:11 +03:00
if (likely(!(filp->f_mode & FMODE_PATH))) {
dnotify_flush(filp, id);
locks_remove_posix(filp, id);
}
return retval;
}
int filp_close(struct file *filp, fl_owner_t id)
{
int retval;
retval = filp_flush(filp, id);
fput(filp);
return retval;
}
EXPORT_SYMBOL(filp_close);
/*
* Careful here! We test whether the file pointer is NULL before
* releasing the fd. This ensures that one clone task can't release
* an fd while another clone is opening it.
*/
SYSCALL_DEFINE1(close, unsigned int, fd)
{
int retval;
struct file *file;
file = close_fd_get_file(fd);
if (!file)
return -EBADF;
retval = filp_flush(file, current->files);
/*
* We're returning to user space. Don't bother
* with any delayed fput() cases.
*/
__fput_sync(file);
2006-09-29 13:00:13 +04:00
/* can't restart close syscall because file table entry was cleared */
if (unlikely(retval == -ERESTARTSYS ||
retval == -ERESTARTNOINTR ||
retval == -ERESTARTNOHAND ||
retval == -ERESTART_RESTARTBLOCK))
retval = -EINTR;
return retval;
}
open: add close_range() This adds the close_range() syscall. It allows to efficiently close a range of file descriptors up to all file descriptors of a calling task. I was contacted by FreeBSD as they wanted to have the same close_range() syscall as we proposed here. We've coordinated this and in the meantime, Kyle was fast enough to merge close_range() into FreeBSD already in April: https://reviews.freebsd.org/D21627 https://svnweb.freebsd.org/base?view=revision&revision=359836 and the current plan is to backport close_range() to FreeBSD 12.2 (cf. [2]) once its merged in Linux too. Python is in the process of switching to close_range() on FreeBSD and they are waiting on us to merge this to switch on Linux as well: https://bugs.python.org/issue38061 The syscall came up in a recent discussion around the new mount API and making new file descriptor types cloexec by default. During this discussion, Al suggested the close_range() syscall (cf. [1]). Note, a syscall in this manner has been requested by various people over time. First, it helps to close all file descriptors of an exec()ing task. This can be done safely via (quoting Al's example from [1] verbatim): /* that exec is sensitive */ unshare(CLONE_FILES); /* we don't want anything past stderr here */ close_range(3, ~0U); execve(....); The code snippet above is one way of working around the problem that file descriptors are not cloexec by default. This is aggravated by the fact that we can't just switch them over without massively regressing userspace. For a whole class of programs having an in-kernel method of closing all file descriptors is very helpful (e.g. demons, service managers, programming language standard libraries, container managers etc.). (Please note, unshare(CLONE_FILES) should only be needed if the calling task is multi-threaded and shares the file descriptor table with another thread in which case two threads could race with one thread allocating file descriptors and the other one closing them via close_range(). For the general case close_range() before the execve() is sufficient.) Second, it allows userspace to avoid implementing closing all file descriptors by parsing through /proc/<pid>/fd/* and calling close() on each file descriptor. From looking at various large(ish) userspace code bases this or similar patterns are very common in: - service managers (cf. [4]) - libcs (cf. [6]) - container runtimes (cf. [5]) - programming language runtimes/standard libraries - Python (cf. [2]) - Rust (cf. [7], [8]) As Dmitry pointed out there's even a long-standing glibc bug about missing kernel support for this task (cf. [3]). In addition, the syscall will also work for tasks that do not have procfs mounted and on kernels that do not have procfs support compiled in. In such situations the only way to make sure that all file descriptors are closed is to call close() on each file descriptor up to UINT_MAX or RLIMIT_NOFILE, OPEN_MAX trickery (cf. comment [8] on Rust). The performance is striking. For good measure, comparing the following simple close_all_fds() userspace implementation that is essentially just glibc's version in [6]: static int close_all_fds(void) { int dir_fd; DIR *dir; struct dirent *direntp; dir = opendir("/proc/self/fd"); if (!dir) return -1; dir_fd = dirfd(dir); while ((direntp = readdir(dir))) { int fd; if (strcmp(direntp->d_name, ".") == 0) continue; if (strcmp(direntp->d_name, "..") == 0) continue; fd = atoi(direntp->d_name); if (fd == dir_fd || fd == 0 || fd == 1 || fd == 2) continue; close(fd); } closedir(dir); return 0; } to close_range() yields: 1. closing 4 open files: - close_all_fds(): ~280 us - close_range(): ~24 us 2. closing 1000 open files: - close_all_fds(): ~5000 us - close_range(): ~800 us close_range() is designed to allow for some flexibility. Specifically, it does not simply always close all open file descriptors of a task. Instead, callers can specify an upper bound. This is e.g. useful for scenarios where specific file descriptors are created with well-known numbers that are supposed to be excluded from getting closed. For extra paranoia close_range() comes with a flags argument. This can e.g. be used to implement extension. Once can imagine userspace wanting to stop at the first error instead of ignoring errors under certain circumstances. There might be other valid ideas in the future. In any case, a flag argument doesn't hurt and keeps us on the safe side. From an implementation side this is kept rather dumb. It saw some input from David and Jann but all nonsense is obviously my own! - Errors to close file descriptors are currently ignored. (Could be changed by setting a flag in the future if needed.) - __close_range() is a rather simplistic wrapper around __close_fd(). My reasoning behind this is based on the nature of how __close_fd() needs to release an fd. But maybe I misunderstood specifics: We take the files_lock and rcu-dereference the fdtable of the calling task, we find the entry in the fdtable, get the file and need to release files_lock before calling filp_close(). In the meantime the fdtable might have been altered so we can't just retake the spinlock and keep the old rcu-reference of the fdtable around. Instead we need to grab a fresh reference to the fdtable. If my reasoning is correct then there's really no point in fancyfying __close_range(): We just need to rcu-dereference the fdtable of the calling task once to cap the max_fd value correctly and then go on calling __close_fd() in a loop. /* References */ [1]: https://lore.kernel.org/lkml/20190516165021.GD17978@ZenIV.linux.org.uk/ [2]: https://github.com/python/cpython/blob/9e4f2f3a6b8ee995c365e86d976937c141d867f8/Modules/_posixsubprocess.c#L220 [3]: https://sourceware.org/bugzilla/show_bug.cgi?id=10353#c7 [4]: https://github.com/systemd/systemd/blob/5238e9575906297608ff802a27e2ff9effa3b338/src/basic/fd-util.c#L217 [5]: https://github.com/lxc/lxc/blob/ddf4b77e11a4d08f09b7b9cd13e593f8c047edc5/src/lxc/start.c#L236 [6]: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/grantpt.c;h=2030e07fa6e652aac32c775b8c6e005844c3c4eb;hb=HEAD#l17 Note that this is an internal implementation that is not exported. Currently, libc seems to not provide an exported version of this because of missing kernel support to do this. Note, in a recent patch series Florian made grantpt() a nop thereby removing the code referenced here. [7]: https://github.com/rust-lang/rust/issues/12148 [8]: https://github.com/rust-lang/rust/blob/5f47c0613ed4eb46fca3633c1297364c09e5e451/src/libstd/sys/unix/process2.rs#L303-L308 Rust's solution is slightly different but is equally unperformant. Rust calls getdtablesize() which is a glibc library function that simply returns the current RLIMIT_NOFILE or OPEN_MAX values. Rust then goes on to call close() on each fd. That's obviously overkill for most tasks. Rarely, tasks - especially non-demons - hit RLIMIT_NOFILE or OPEN_MAX. Let's be nice and assume an unprivileged user with RLIMIT_NOFILE set to 1024. Even in this case, there's a very high chance that in the common case Rust is calling the close() syscall 1021 times pointlessly if the task just has 0, 1, and 2 open. Suggested-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Kyle Evans <self@kyle-evans.net> Cc: Jann Horn <jannh@google.com> Cc: David Howells <dhowells@redhat.com> Cc: Dmitry V. Levin <ldv@altlinux.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Florian Weimer <fweimer@redhat.com> Cc: linux-api@vger.kernel.org
2019-05-24 12:30:34 +03:00
/**
* sys_close_range() - Close all file descriptors in a given range.
open: add close_range() This adds the close_range() syscall. It allows to efficiently close a range of file descriptors up to all file descriptors of a calling task. I was contacted by FreeBSD as they wanted to have the same close_range() syscall as we proposed here. We've coordinated this and in the meantime, Kyle was fast enough to merge close_range() into FreeBSD already in April: https://reviews.freebsd.org/D21627 https://svnweb.freebsd.org/base?view=revision&revision=359836 and the current plan is to backport close_range() to FreeBSD 12.2 (cf. [2]) once its merged in Linux too. Python is in the process of switching to close_range() on FreeBSD and they are waiting on us to merge this to switch on Linux as well: https://bugs.python.org/issue38061 The syscall came up in a recent discussion around the new mount API and making new file descriptor types cloexec by default. During this discussion, Al suggested the close_range() syscall (cf. [1]). Note, a syscall in this manner has been requested by various people over time. First, it helps to close all file descriptors of an exec()ing task. This can be done safely via (quoting Al's example from [1] verbatim): /* that exec is sensitive */ unshare(CLONE_FILES); /* we don't want anything past stderr here */ close_range(3, ~0U); execve(....); The code snippet above is one way of working around the problem that file descriptors are not cloexec by default. This is aggravated by the fact that we can't just switch them over without massively regressing userspace. For a whole class of programs having an in-kernel method of closing all file descriptors is very helpful (e.g. demons, service managers, programming language standard libraries, container managers etc.). (Please note, unshare(CLONE_FILES) should only be needed if the calling task is multi-threaded and shares the file descriptor table with another thread in which case two threads could race with one thread allocating file descriptors and the other one closing them via close_range(). For the general case close_range() before the execve() is sufficient.) Second, it allows userspace to avoid implementing closing all file descriptors by parsing through /proc/<pid>/fd/* and calling close() on each file descriptor. From looking at various large(ish) userspace code bases this or similar patterns are very common in: - service managers (cf. [4]) - libcs (cf. [6]) - container runtimes (cf. [5]) - programming language runtimes/standard libraries - Python (cf. [2]) - Rust (cf. [7], [8]) As Dmitry pointed out there's even a long-standing glibc bug about missing kernel support for this task (cf. [3]). In addition, the syscall will also work for tasks that do not have procfs mounted and on kernels that do not have procfs support compiled in. In such situations the only way to make sure that all file descriptors are closed is to call close() on each file descriptor up to UINT_MAX or RLIMIT_NOFILE, OPEN_MAX trickery (cf. comment [8] on Rust). The performance is striking. For good measure, comparing the following simple close_all_fds() userspace implementation that is essentially just glibc's version in [6]: static int close_all_fds(void) { int dir_fd; DIR *dir; struct dirent *direntp; dir = opendir("/proc/self/fd"); if (!dir) return -1; dir_fd = dirfd(dir); while ((direntp = readdir(dir))) { int fd; if (strcmp(direntp->d_name, ".") == 0) continue; if (strcmp(direntp->d_name, "..") == 0) continue; fd = atoi(direntp->d_name); if (fd == dir_fd || fd == 0 || fd == 1 || fd == 2) continue; close(fd); } closedir(dir); return 0; } to close_range() yields: 1. closing 4 open files: - close_all_fds(): ~280 us - close_range(): ~24 us 2. closing 1000 open files: - close_all_fds(): ~5000 us - close_range(): ~800 us close_range() is designed to allow for some flexibility. Specifically, it does not simply always close all open file descriptors of a task. Instead, callers can specify an upper bound. This is e.g. useful for scenarios where specific file descriptors are created with well-known numbers that are supposed to be excluded from getting closed. For extra paranoia close_range() comes with a flags argument. This can e.g. be used to implement extension. Once can imagine userspace wanting to stop at the first error instead of ignoring errors under certain circumstances. There might be other valid ideas in the future. In any case, a flag argument doesn't hurt and keeps us on the safe side. From an implementation side this is kept rather dumb. It saw some input from David and Jann but all nonsense is obviously my own! - Errors to close file descriptors are currently ignored. (Could be changed by setting a flag in the future if needed.) - __close_range() is a rather simplistic wrapper around __close_fd(). My reasoning behind this is based on the nature of how __close_fd() needs to release an fd. But maybe I misunderstood specifics: We take the files_lock and rcu-dereference the fdtable of the calling task, we find the entry in the fdtable, get the file and need to release files_lock before calling filp_close(). In the meantime the fdtable might have been altered so we can't just retake the spinlock and keep the old rcu-reference of the fdtable around. Instead we need to grab a fresh reference to the fdtable. If my reasoning is correct then there's really no point in fancyfying __close_range(): We just need to rcu-dereference the fdtable of the calling task once to cap the max_fd value correctly and then go on calling __close_fd() in a loop. /* References */ [1]: https://lore.kernel.org/lkml/20190516165021.GD17978@ZenIV.linux.org.uk/ [2]: https://github.com/python/cpython/blob/9e4f2f3a6b8ee995c365e86d976937c141d867f8/Modules/_posixsubprocess.c#L220 [3]: https://sourceware.org/bugzilla/show_bug.cgi?id=10353#c7 [4]: https://github.com/systemd/systemd/blob/5238e9575906297608ff802a27e2ff9effa3b338/src/basic/fd-util.c#L217 [5]: https://github.com/lxc/lxc/blob/ddf4b77e11a4d08f09b7b9cd13e593f8c047edc5/src/lxc/start.c#L236 [6]: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/grantpt.c;h=2030e07fa6e652aac32c775b8c6e005844c3c4eb;hb=HEAD#l17 Note that this is an internal implementation that is not exported. Currently, libc seems to not provide an exported version of this because of missing kernel support to do this. Note, in a recent patch series Florian made grantpt() a nop thereby removing the code referenced here. [7]: https://github.com/rust-lang/rust/issues/12148 [8]: https://github.com/rust-lang/rust/blob/5f47c0613ed4eb46fca3633c1297364c09e5e451/src/libstd/sys/unix/process2.rs#L303-L308 Rust's solution is slightly different but is equally unperformant. Rust calls getdtablesize() which is a glibc library function that simply returns the current RLIMIT_NOFILE or OPEN_MAX values. Rust then goes on to call close() on each fd. That's obviously overkill for most tasks. Rarely, tasks - especially non-demons - hit RLIMIT_NOFILE or OPEN_MAX. Let's be nice and assume an unprivileged user with RLIMIT_NOFILE set to 1024. Even in this case, there's a very high chance that in the common case Rust is calling the close() syscall 1021 times pointlessly if the task just has 0, 1, and 2 open. Suggested-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Kyle Evans <self@kyle-evans.net> Cc: Jann Horn <jannh@google.com> Cc: David Howells <dhowells@redhat.com> Cc: Dmitry V. Levin <ldv@altlinux.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Florian Weimer <fweimer@redhat.com> Cc: linux-api@vger.kernel.org
2019-05-24 12:30:34 +03:00
*
* @fd: starting file descriptor to close
* @max_fd: last file descriptor to close
* @flags: reserved for future extensions
*
* This closes a range of file descriptors. All file descriptors
* from @fd up to and including @max_fd are closed.
* Currently, errors to close a given file descriptor are ignored.
*/
SYSCALL_DEFINE3(close_range, unsigned int, fd, unsigned int, max_fd,
unsigned int, flags)
{
return __close_range(fd, max_fd, flags);
open: add close_range() This adds the close_range() syscall. It allows to efficiently close a range of file descriptors up to all file descriptors of a calling task. I was contacted by FreeBSD as they wanted to have the same close_range() syscall as we proposed here. We've coordinated this and in the meantime, Kyle was fast enough to merge close_range() into FreeBSD already in April: https://reviews.freebsd.org/D21627 https://svnweb.freebsd.org/base?view=revision&revision=359836 and the current plan is to backport close_range() to FreeBSD 12.2 (cf. [2]) once its merged in Linux too. Python is in the process of switching to close_range() on FreeBSD and they are waiting on us to merge this to switch on Linux as well: https://bugs.python.org/issue38061 The syscall came up in a recent discussion around the new mount API and making new file descriptor types cloexec by default. During this discussion, Al suggested the close_range() syscall (cf. [1]). Note, a syscall in this manner has been requested by various people over time. First, it helps to close all file descriptors of an exec()ing task. This can be done safely via (quoting Al's example from [1] verbatim): /* that exec is sensitive */ unshare(CLONE_FILES); /* we don't want anything past stderr here */ close_range(3, ~0U); execve(....); The code snippet above is one way of working around the problem that file descriptors are not cloexec by default. This is aggravated by the fact that we can't just switch them over without massively regressing userspace. For a whole class of programs having an in-kernel method of closing all file descriptors is very helpful (e.g. demons, service managers, programming language standard libraries, container managers etc.). (Please note, unshare(CLONE_FILES) should only be needed if the calling task is multi-threaded and shares the file descriptor table with another thread in which case two threads could race with one thread allocating file descriptors and the other one closing them via close_range(). For the general case close_range() before the execve() is sufficient.) Second, it allows userspace to avoid implementing closing all file descriptors by parsing through /proc/<pid>/fd/* and calling close() on each file descriptor. From looking at various large(ish) userspace code bases this or similar patterns are very common in: - service managers (cf. [4]) - libcs (cf. [6]) - container runtimes (cf. [5]) - programming language runtimes/standard libraries - Python (cf. [2]) - Rust (cf. [7], [8]) As Dmitry pointed out there's even a long-standing glibc bug about missing kernel support for this task (cf. [3]). In addition, the syscall will also work for tasks that do not have procfs mounted and on kernels that do not have procfs support compiled in. In such situations the only way to make sure that all file descriptors are closed is to call close() on each file descriptor up to UINT_MAX or RLIMIT_NOFILE, OPEN_MAX trickery (cf. comment [8] on Rust). The performance is striking. For good measure, comparing the following simple close_all_fds() userspace implementation that is essentially just glibc's version in [6]: static int close_all_fds(void) { int dir_fd; DIR *dir; struct dirent *direntp; dir = opendir("/proc/self/fd"); if (!dir) return -1; dir_fd = dirfd(dir); while ((direntp = readdir(dir))) { int fd; if (strcmp(direntp->d_name, ".") == 0) continue; if (strcmp(direntp->d_name, "..") == 0) continue; fd = atoi(direntp->d_name); if (fd == dir_fd || fd == 0 || fd == 1 || fd == 2) continue; close(fd); } closedir(dir); return 0; } to close_range() yields: 1. closing 4 open files: - close_all_fds(): ~280 us - close_range(): ~24 us 2. closing 1000 open files: - close_all_fds(): ~5000 us - close_range(): ~800 us close_range() is designed to allow for some flexibility. Specifically, it does not simply always close all open file descriptors of a task. Instead, callers can specify an upper bound. This is e.g. useful for scenarios where specific file descriptors are created with well-known numbers that are supposed to be excluded from getting closed. For extra paranoia close_range() comes with a flags argument. This can e.g. be used to implement extension. Once can imagine userspace wanting to stop at the first error instead of ignoring errors under certain circumstances. There might be other valid ideas in the future. In any case, a flag argument doesn't hurt and keeps us on the safe side. From an implementation side this is kept rather dumb. It saw some input from David and Jann but all nonsense is obviously my own! - Errors to close file descriptors are currently ignored. (Could be changed by setting a flag in the future if needed.) - __close_range() is a rather simplistic wrapper around __close_fd(). My reasoning behind this is based on the nature of how __close_fd() needs to release an fd. But maybe I misunderstood specifics: We take the files_lock and rcu-dereference the fdtable of the calling task, we find the entry in the fdtable, get the file and need to release files_lock before calling filp_close(). In the meantime the fdtable might have been altered so we can't just retake the spinlock and keep the old rcu-reference of the fdtable around. Instead we need to grab a fresh reference to the fdtable. If my reasoning is correct then there's really no point in fancyfying __close_range(): We just need to rcu-dereference the fdtable of the calling task once to cap the max_fd value correctly and then go on calling __close_fd() in a loop. /* References */ [1]: https://lore.kernel.org/lkml/20190516165021.GD17978@ZenIV.linux.org.uk/ [2]: https://github.com/python/cpython/blob/9e4f2f3a6b8ee995c365e86d976937c141d867f8/Modules/_posixsubprocess.c#L220 [3]: https://sourceware.org/bugzilla/show_bug.cgi?id=10353#c7 [4]: https://github.com/systemd/systemd/blob/5238e9575906297608ff802a27e2ff9effa3b338/src/basic/fd-util.c#L217 [5]: https://github.com/lxc/lxc/blob/ddf4b77e11a4d08f09b7b9cd13e593f8c047edc5/src/lxc/start.c#L236 [6]: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/grantpt.c;h=2030e07fa6e652aac32c775b8c6e005844c3c4eb;hb=HEAD#l17 Note that this is an internal implementation that is not exported. Currently, libc seems to not provide an exported version of this because of missing kernel support to do this. Note, in a recent patch series Florian made grantpt() a nop thereby removing the code referenced here. [7]: https://github.com/rust-lang/rust/issues/12148 [8]: https://github.com/rust-lang/rust/blob/5f47c0613ed4eb46fca3633c1297364c09e5e451/src/libstd/sys/unix/process2.rs#L303-L308 Rust's solution is slightly different but is equally unperformant. Rust calls getdtablesize() which is a glibc library function that simply returns the current RLIMIT_NOFILE or OPEN_MAX values. Rust then goes on to call close() on each fd. That's obviously overkill for most tasks. Rarely, tasks - especially non-demons - hit RLIMIT_NOFILE or OPEN_MAX. Let's be nice and assume an unprivileged user with RLIMIT_NOFILE set to 1024. Even in this case, there's a very high chance that in the common case Rust is calling the close() syscall 1021 times pointlessly if the task just has 0, 1, and 2 open. Suggested-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Kyle Evans <self@kyle-evans.net> Cc: Jann Horn <jannh@google.com> Cc: David Howells <dhowells@redhat.com> Cc: Dmitry V. Levin <ldv@altlinux.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Florian Weimer <fweimer@redhat.com> Cc: linux-api@vger.kernel.org
2019-05-24 12:30:34 +03:00
}
/*
* This routine simulates a hangup on the tty, to arrange that users
* are given clean terminals at login time.
*/
SYSCALL_DEFINE0(vhangup)
{
if (capable(CAP_SYS_TTY_CONFIG)) {
tty_vhangup_self();
return 0;
}
return -EPERM;
}
/*
* Called when an inode is about to be open.
* We use this to disallow opening large files on 32bit systems if
* the caller didn't specify O_LARGEFILE. On 64bit systems we force
* on this flag in sys_open.
*/
int generic_file_open(struct inode * inode, struct file * filp)
{
if (!(filp->f_flags & O_LARGEFILE) && i_size_read(inode) > MAX_NON_LFS)
return -EOVERFLOW;
return 0;
}
EXPORT_SYMBOL(generic_file_open);
/*
* This is used by subsystems that don't want seekable
* file descriptors. The function is not supposed to ever fail, the only
* reason it returns an 'int' and not 'void' is so that it can be plugged
* directly into file_operations structure.
*/
int nonseekable_open(struct inode *inode, struct file *filp)
{
filp->f_mode &= ~(FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE);
return 0;
}
EXPORT_SYMBOL(nonseekable_open);
fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock Commit 9c225f2655e3 ("vfs: atomic f_pos accesses as per POSIX") added locking for file.f_pos access and in particular made concurrent read and write not possible - now both those functions take f_pos lock for the whole run, and so if e.g. a read is blocked waiting for data, write will deadlock waiting for that read to complete. This caused regression for stream-like files where previously read and write could run simultaneously, but after that patch could not do so anymore. See e.g. commit 581d21a2d02a ("xenbus: fix deadlock on writes to /proc/xen/xenbus") which fixes such regression for particular case of /proc/xen/xenbus. The patch that added f_pos lock in 2014 did so to guarantee POSIX thread safety for read/write/lseek and added the locking to file descriptors of all regular files. In 2014 that thread-safety problem was not new as it was already discussed earlier in 2006. However even though 2006'th version of Linus's patch was adding f_pos locking "only for files that are marked seekable with FMODE_LSEEK (thus avoiding the stream-like objects like pipes and sockets)", the 2014 version - the one that actually made it into the tree as 9c225f2655e3 - is doing so irregardless of whether a file is seekable or not. See https://lore.kernel.org/lkml/53022DB1.4070805@gmail.com/ https://lwn.net/Articles/180387 https://lwn.net/Articles/180396 for historic context. The reason that it did so is, probably, that there are many files that are marked non-seekable, but e.g. their read implementation actually depends on knowing current position to correctly handle the read. Some examples: kernel/power/user.c snapshot_read fs/debugfs/file.c u32_array_read fs/fuse/control.c fuse_conn_waiting_read + ... drivers/hwmon/asus_atk0110.c atk_debugfs_ggrp_read arch/s390/hypfs/inode.c hypfs_read_iter ... Despite that, many nonseekable_open users implement read and write with pure stream semantics - they don't depend on passed ppos at all. And for those cases where read could wait for something inside, it creates a situation similar to xenbus - the write could be never made to go until read is done, and read is waiting for some, potentially external, event, for potentially unbounded time -> deadlock. Besides xenbus, there are 14 such places in the kernel that I've found with semantic patch (see below): drivers/xen/evtchn.c:667:8-24: ERROR: evtchn_fops: .read() can deadlock .write() drivers/isdn/capi/capi.c:963:8-24: ERROR: capi_fops: .read() can deadlock .write() drivers/input/evdev.c:527:1-17: ERROR: evdev_fops: .read() can deadlock .write() drivers/char/pcmcia/cm4000_cs.c:1685:7-23: ERROR: cm4000_fops: .read() can deadlock .write() net/rfkill/core.c:1146:8-24: ERROR: rfkill_fops: .read() can deadlock .write() drivers/s390/char/fs3270.c:488:1-17: ERROR: fs3270_fops: .read() can deadlock .write() drivers/usb/misc/ldusb.c:310:1-17: ERROR: ld_usb_fops: .read() can deadlock .write() drivers/hid/uhid.c:635:1-17: ERROR: uhid_fops: .read() can deadlock .write() net/batman-adv/icmp_socket.c:80:1-17: ERROR: batadv_fops: .read() can deadlock .write() drivers/media/rc/lirc_dev.c:198:1-17: ERROR: lirc_fops: .read() can deadlock .write() drivers/leds/uleds.c:77:1-17: ERROR: uleds_fops: .read() can deadlock .write() drivers/input/misc/uinput.c:400:1-17: ERROR: uinput_fops: .read() can deadlock .write() drivers/infiniband/core/user_mad.c:985:7-23: ERROR: umad_fops: .read() can deadlock .write() drivers/gnss/core.c:45:1-17: ERROR: gnss_fops: .read() can deadlock .write() In addition to the cases above another regression caused by f_pos locking is that now FUSE filesystems that implement open with FOPEN_NONSEEKABLE flag, can no longer implement bidirectional stream-like files - for the same reason as above e.g. read can deadlock write locking on file.f_pos in the kernel. FUSE's FOPEN_NONSEEKABLE was added in 2008 in a7c1b990f715 ("fuse: implement nonseekable open") to support OSSPD. OSSPD implements /dev/dsp in userspace with FOPEN_NONSEEKABLE flag, with corresponding read and write routines not depending on current position at all, and with both read and write being potentially blocking operations: See https://github.com/libfuse/osspd https://lwn.net/Articles/308445 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1406 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1438-L1477 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1479-L1510 Corresponding libfuse example/test also describes FOPEN_NONSEEKABLE as "somewhat pipe-like files ..." with read handler not using offset. However that test implements only read without write and cannot exercise the deadlock scenario: https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L124-L131 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L146-L163 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L209-L216 I've actually hit the read vs write deadlock for real while implementing my FUSE filesystem where there is /head/watch file, for which open creates separate bidirectional socket-like stream in between filesystem and its user with both read and write being later performed simultaneously. And there it is semantically not easy to split the stream into two separate read-only and write-only channels: https://lab.nexedi.com/kirr/wendelin.core/blob/f13aa600/wcfs/wcfs.go#L88-169 Let's fix this regression. The plan is: 1. We can't change nonseekable_open to include &~FMODE_ATOMIC_POS - doing so would break many in-kernel nonseekable_open users which actually use ppos in read/write handlers. 2. Add stream_open() to kernel to open stream-like non-seekable file descriptors. Read and write on such file descriptors would never use nor change ppos. And with that property on stream-like files read and write will be running without taking f_pos lock - i.e. read and write could be running simultaneously. 3. With semantic patch search and convert to stream_open all in-kernel nonseekable_open users for which read and write actually do not depend on ppos and where there is no other methods in file_operations which assume @offset access. 4. Add FOPEN_STREAM to fs/fuse/ and open in-kernel file-descriptors via steam_open if that bit is present in filesystem open reply. It was tempting to change fs/fuse/ open handler to use stream_open instead of nonseekable_open on just FOPEN_NONSEEKABLE flags, but grepping through Debian codesearch shows users of FOPEN_NONSEEKABLE, and in particular GVFS which actually uses offset in its read and write handlers https://codesearch.debian.net/search?q=-%3Enonseekable+%3D https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1080 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1247-1346 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1399-1481 so if we would do such a change it will break a real user. 5. Add stream_open and FOPEN_STREAM handling to stable kernels starting from v3.14+ (the kernel where 9c225f2655 first appeared). This will allow to patch OSSPD and other FUSE filesystems that provide stream-like files to return FOPEN_STREAM | FOPEN_NONSEEKABLE in their open handler and this way avoid the deadlock on all kernel versions. This should work because fs/fuse/ ignores unknown open flags returned from a filesystem and so passing FOPEN_STREAM to a kernel that is not aware of this flag cannot hurt. In turn the kernel that is not aware of FOPEN_STREAM will be < v3.14 where just FOPEN_NONSEEKABLE is sufficient to implement streams without read vs write deadlock. This patch adds stream_open, converts /proc/xen/xenbus to it and adds semantic patch to automatically locate in-kernel places that are either required to be converted due to read vs write deadlock, or that are just safe to be converted because read and write do not use ppos and there are no other funky methods in file_operations. Regarding semantic patch I've verified each generated change manually - that it is correct to convert - and each other nonseekable_open instance left - that it is either not correct to convert there, or that it is not converted due to current stream_open.cocci limitations. The script also does not convert files that should be valid to convert, but that currently have .llseek = noop_llseek or generic_file_llseek for unknown reason despite file being opened with nonseekable_open (e.g. drivers/input/mousedev.c) Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Yongzhi Pan <panyongzhi@gmail.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Juergen Gross <jgross@suse.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Tejun Heo <tj@kernel.org> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Christoph Hellwig <hch@lst.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Julia Lawall <Julia.Lawall@lip6.fr> Cc: Nikolaus Rath <Nikolaus@rath.org> Cc: Han-Wen Nienhuys <hanwen@google.com> Signed-off-by: Kirill Smelkov <kirr@nexedi.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-03-27 01:20:43 +03:00
/*
* stream_open is used by subsystems that want stream-like file descriptors.
* Such file descriptors are not seekable and don't have notion of position
vfs: pass ppos=NULL to .read()/.write() of FMODE_STREAM files This amends commit 10dce8af3422 ("fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock") in how position is passed into .read()/.write() handler for stream-like files: Rasmus noticed that we currently pass 0 as position and ignore any position change if that is done by a file implementation. This papers over bugs if ppos is used in files that declare themselves as being stream-like as such bugs will go unnoticed. Even if a file implementation is correctly converted into using stream_open, its read/write later could be changed to use ppos and even though that won't be working correctly, that bug might go unnoticed without someone doing wrong behaviour analysis. It is thus better to pass ppos=NULL into read/write for stream-like files as that don't give any chance for ppos usage bugs because it will oops if ppos is ever used inside .read() or .write(). Note 1: rw_verify_area, new_sync_{read,write} needs to be updated because they are called by vfs_read/vfs_write & friends before file_operations .read/.write . Note 2: if file backend uses new-style .read_iter/.write_iter, position is still passed into there as non-pointer kiocb.ki_pos . Currently stream_open.cocci (semantic patch added by 10dce8af3422) ignores files whose file_operations has *_iter methods. Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> Signed-off-by: Kirill Smelkov <kirr@nexedi.com>
2019-04-12 12:31:57 +03:00
* (file.f_pos is always 0 and ppos passed to .read()/.write() is always NULL).
* Contrary to file descriptors of other regular files, .read() and .write()
* can run simultaneously.
fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock Commit 9c225f2655e3 ("vfs: atomic f_pos accesses as per POSIX") added locking for file.f_pos access and in particular made concurrent read and write not possible - now both those functions take f_pos lock for the whole run, and so if e.g. a read is blocked waiting for data, write will deadlock waiting for that read to complete. This caused regression for stream-like files where previously read and write could run simultaneously, but after that patch could not do so anymore. See e.g. commit 581d21a2d02a ("xenbus: fix deadlock on writes to /proc/xen/xenbus") which fixes such regression for particular case of /proc/xen/xenbus. The patch that added f_pos lock in 2014 did so to guarantee POSIX thread safety for read/write/lseek and added the locking to file descriptors of all regular files. In 2014 that thread-safety problem was not new as it was already discussed earlier in 2006. However even though 2006'th version of Linus's patch was adding f_pos locking "only for files that are marked seekable with FMODE_LSEEK (thus avoiding the stream-like objects like pipes and sockets)", the 2014 version - the one that actually made it into the tree as 9c225f2655e3 - is doing so irregardless of whether a file is seekable or not. See https://lore.kernel.org/lkml/53022DB1.4070805@gmail.com/ https://lwn.net/Articles/180387 https://lwn.net/Articles/180396 for historic context. The reason that it did so is, probably, that there are many files that are marked non-seekable, but e.g. their read implementation actually depends on knowing current position to correctly handle the read. Some examples: kernel/power/user.c snapshot_read fs/debugfs/file.c u32_array_read fs/fuse/control.c fuse_conn_waiting_read + ... drivers/hwmon/asus_atk0110.c atk_debugfs_ggrp_read arch/s390/hypfs/inode.c hypfs_read_iter ... Despite that, many nonseekable_open users implement read and write with pure stream semantics - they don't depend on passed ppos at all. And for those cases where read could wait for something inside, it creates a situation similar to xenbus - the write could be never made to go until read is done, and read is waiting for some, potentially external, event, for potentially unbounded time -> deadlock. Besides xenbus, there are 14 such places in the kernel that I've found with semantic patch (see below): drivers/xen/evtchn.c:667:8-24: ERROR: evtchn_fops: .read() can deadlock .write() drivers/isdn/capi/capi.c:963:8-24: ERROR: capi_fops: .read() can deadlock .write() drivers/input/evdev.c:527:1-17: ERROR: evdev_fops: .read() can deadlock .write() drivers/char/pcmcia/cm4000_cs.c:1685:7-23: ERROR: cm4000_fops: .read() can deadlock .write() net/rfkill/core.c:1146:8-24: ERROR: rfkill_fops: .read() can deadlock .write() drivers/s390/char/fs3270.c:488:1-17: ERROR: fs3270_fops: .read() can deadlock .write() drivers/usb/misc/ldusb.c:310:1-17: ERROR: ld_usb_fops: .read() can deadlock .write() drivers/hid/uhid.c:635:1-17: ERROR: uhid_fops: .read() can deadlock .write() net/batman-adv/icmp_socket.c:80:1-17: ERROR: batadv_fops: .read() can deadlock .write() drivers/media/rc/lirc_dev.c:198:1-17: ERROR: lirc_fops: .read() can deadlock .write() drivers/leds/uleds.c:77:1-17: ERROR: uleds_fops: .read() can deadlock .write() drivers/input/misc/uinput.c:400:1-17: ERROR: uinput_fops: .read() can deadlock .write() drivers/infiniband/core/user_mad.c:985:7-23: ERROR: umad_fops: .read() can deadlock .write() drivers/gnss/core.c:45:1-17: ERROR: gnss_fops: .read() can deadlock .write() In addition to the cases above another regression caused by f_pos locking is that now FUSE filesystems that implement open with FOPEN_NONSEEKABLE flag, can no longer implement bidirectional stream-like files - for the same reason as above e.g. read can deadlock write locking on file.f_pos in the kernel. FUSE's FOPEN_NONSEEKABLE was added in 2008 in a7c1b990f715 ("fuse: implement nonseekable open") to support OSSPD. OSSPD implements /dev/dsp in userspace with FOPEN_NONSEEKABLE flag, with corresponding read and write routines not depending on current position at all, and with both read and write being potentially blocking operations: See https://github.com/libfuse/osspd https://lwn.net/Articles/308445 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1406 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1438-L1477 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1479-L1510 Corresponding libfuse example/test also describes FOPEN_NONSEEKABLE as "somewhat pipe-like files ..." with read handler not using offset. However that test implements only read without write and cannot exercise the deadlock scenario: https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L124-L131 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L146-L163 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L209-L216 I've actually hit the read vs write deadlock for real while implementing my FUSE filesystem where there is /head/watch file, for which open creates separate bidirectional socket-like stream in between filesystem and its user with both read and write being later performed simultaneously. And there it is semantically not easy to split the stream into two separate read-only and write-only channels: https://lab.nexedi.com/kirr/wendelin.core/blob/f13aa600/wcfs/wcfs.go#L88-169 Let's fix this regression. The plan is: 1. We can't change nonseekable_open to include &~FMODE_ATOMIC_POS - doing so would break many in-kernel nonseekable_open users which actually use ppos in read/write handlers. 2. Add stream_open() to kernel to open stream-like non-seekable file descriptors. Read and write on such file descriptors would never use nor change ppos. And with that property on stream-like files read and write will be running without taking f_pos lock - i.e. read and write could be running simultaneously. 3. With semantic patch search and convert to stream_open all in-kernel nonseekable_open users for which read and write actually do not depend on ppos and where there is no other methods in file_operations which assume @offset access. 4. Add FOPEN_STREAM to fs/fuse/ and open in-kernel file-descriptors via steam_open if that bit is present in filesystem open reply. It was tempting to change fs/fuse/ open handler to use stream_open instead of nonseekable_open on just FOPEN_NONSEEKABLE flags, but grepping through Debian codesearch shows users of FOPEN_NONSEEKABLE, and in particular GVFS which actually uses offset in its read and write handlers https://codesearch.debian.net/search?q=-%3Enonseekable+%3D https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1080 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1247-1346 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1399-1481 so if we would do such a change it will break a real user. 5. Add stream_open and FOPEN_STREAM handling to stable kernels starting from v3.14+ (the kernel where 9c225f2655 first appeared). This will allow to patch OSSPD and other FUSE filesystems that provide stream-like files to return FOPEN_STREAM | FOPEN_NONSEEKABLE in their open handler and this way avoid the deadlock on all kernel versions. This should work because fs/fuse/ ignores unknown open flags returned from a filesystem and so passing FOPEN_STREAM to a kernel that is not aware of this flag cannot hurt. In turn the kernel that is not aware of FOPEN_STREAM will be < v3.14 where just FOPEN_NONSEEKABLE is sufficient to implement streams without read vs write deadlock. This patch adds stream_open, converts /proc/xen/xenbus to it and adds semantic patch to automatically locate in-kernel places that are either required to be converted due to read vs write deadlock, or that are just safe to be converted because read and write do not use ppos and there are no other funky methods in file_operations. Regarding semantic patch I've verified each generated change manually - that it is correct to convert - and each other nonseekable_open instance left - that it is either not correct to convert there, or that it is not converted due to current stream_open.cocci limitations. The script also does not convert files that should be valid to convert, but that currently have .llseek = noop_llseek or generic_file_llseek for unknown reason despite file being opened with nonseekable_open (e.g. drivers/input/mousedev.c) Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Yongzhi Pan <panyongzhi@gmail.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Juergen Gross <jgross@suse.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Tejun Heo <tj@kernel.org> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Christoph Hellwig <hch@lst.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Julia Lawall <Julia.Lawall@lip6.fr> Cc: Nikolaus Rath <Nikolaus@rath.org> Cc: Han-Wen Nienhuys <hanwen@google.com> Signed-off-by: Kirill Smelkov <kirr@nexedi.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-03-27 01:20:43 +03:00
*
* stream_open never fails and is marked to return int so that it could be
* directly used as file_operations.open .
*/
int stream_open(struct inode *inode, struct file *filp)
{
Revert "vfs: properly and reliably lock f_pos in fdget_pos()" This reverts commit 0be0ee71816b2b6725e2b4f32ad6726c9d729777. I was hoping it would be benign to switch over entirely to FMODE_STREAM, and we'd have just a couple of small fixups we'd need, but it looks like we're not quite there yet. While it worked fine on both my desktop and laptop, they are fairly similar in other respects, and run mostly the same loads. Kenneth Crudup reports that it seems to break both his vmware installation and the KDE upower service. In both cases apparently leading to timeouts due to waitinmg for the f_pos lock. There are a number of character devices in particular that definitely want stream-like behavior, but that currently don't get marked as streams, and as a result get the exclusion between concurrent read()/write() on the same file descriptor. Which doesn't work well for them. The most obvious example if this is /dev/console and /dev/tty, which use console_fops and tty_fops respectively (and ptmx_fops for the pty master side). It may be that it's just this that causes problems, but we clearly weren't ready yet. Because there's a number of other likely common cases that don't have llseek implementations and would seem to act as stream devices: /dev/fuse (fuse_dev_operations) /dev/mcelog (mce_chrdev_ops) /dev/mei0 (mei_fops) /dev/net/tun (tun_fops) /dev/nvme0 (nvme_dev_fops) /dev/tpm0 (tpm_fops) /proc/self/ns/mnt (ns_file_operations) /dev/snd/pcm* (snd_pcm_f_ops[]) and while some of these could be trivially automatically detected by the vfs layer when the character device is opened by just noticing that they have no read or write operations either, it often isn't that obvious. Some character devices most definitely do use the file position, even if they don't allow seeking: the firmware update code, for example, uses simple_read_from_buffer() that does use f_pos, but doesn't allow seeking back and forth. We'll revisit this when there's a better way to detect the problem and fix it (possibly with a coccinelle script to do more of the FMODE_STREAM annotations). Reported-by: Kenneth R. Crudup <kenny@panix.com> Cc: Kirill Smelkov <kirr@nexedi.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-11-26 22:34:06 +03:00
filp->f_mode &= ~(FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE | FMODE_ATOMIC_POS);
fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock Commit 9c225f2655e3 ("vfs: atomic f_pos accesses as per POSIX") added locking for file.f_pos access and in particular made concurrent read and write not possible - now both those functions take f_pos lock for the whole run, and so if e.g. a read is blocked waiting for data, write will deadlock waiting for that read to complete. This caused regression for stream-like files where previously read and write could run simultaneously, but after that patch could not do so anymore. See e.g. commit 581d21a2d02a ("xenbus: fix deadlock on writes to /proc/xen/xenbus") which fixes such regression for particular case of /proc/xen/xenbus. The patch that added f_pos lock in 2014 did so to guarantee POSIX thread safety for read/write/lseek and added the locking to file descriptors of all regular files. In 2014 that thread-safety problem was not new as it was already discussed earlier in 2006. However even though 2006'th version of Linus's patch was adding f_pos locking "only for files that are marked seekable with FMODE_LSEEK (thus avoiding the stream-like objects like pipes and sockets)", the 2014 version - the one that actually made it into the tree as 9c225f2655e3 - is doing so irregardless of whether a file is seekable or not. See https://lore.kernel.org/lkml/53022DB1.4070805@gmail.com/ https://lwn.net/Articles/180387 https://lwn.net/Articles/180396 for historic context. The reason that it did so is, probably, that there are many files that are marked non-seekable, but e.g. their read implementation actually depends on knowing current position to correctly handle the read. Some examples: kernel/power/user.c snapshot_read fs/debugfs/file.c u32_array_read fs/fuse/control.c fuse_conn_waiting_read + ... drivers/hwmon/asus_atk0110.c atk_debugfs_ggrp_read arch/s390/hypfs/inode.c hypfs_read_iter ... Despite that, many nonseekable_open users implement read and write with pure stream semantics - they don't depend on passed ppos at all. And for those cases where read could wait for something inside, it creates a situation similar to xenbus - the write could be never made to go until read is done, and read is waiting for some, potentially external, event, for potentially unbounded time -> deadlock. Besides xenbus, there are 14 such places in the kernel that I've found with semantic patch (see below): drivers/xen/evtchn.c:667:8-24: ERROR: evtchn_fops: .read() can deadlock .write() drivers/isdn/capi/capi.c:963:8-24: ERROR: capi_fops: .read() can deadlock .write() drivers/input/evdev.c:527:1-17: ERROR: evdev_fops: .read() can deadlock .write() drivers/char/pcmcia/cm4000_cs.c:1685:7-23: ERROR: cm4000_fops: .read() can deadlock .write() net/rfkill/core.c:1146:8-24: ERROR: rfkill_fops: .read() can deadlock .write() drivers/s390/char/fs3270.c:488:1-17: ERROR: fs3270_fops: .read() can deadlock .write() drivers/usb/misc/ldusb.c:310:1-17: ERROR: ld_usb_fops: .read() can deadlock .write() drivers/hid/uhid.c:635:1-17: ERROR: uhid_fops: .read() can deadlock .write() net/batman-adv/icmp_socket.c:80:1-17: ERROR: batadv_fops: .read() can deadlock .write() drivers/media/rc/lirc_dev.c:198:1-17: ERROR: lirc_fops: .read() can deadlock .write() drivers/leds/uleds.c:77:1-17: ERROR: uleds_fops: .read() can deadlock .write() drivers/input/misc/uinput.c:400:1-17: ERROR: uinput_fops: .read() can deadlock .write() drivers/infiniband/core/user_mad.c:985:7-23: ERROR: umad_fops: .read() can deadlock .write() drivers/gnss/core.c:45:1-17: ERROR: gnss_fops: .read() can deadlock .write() In addition to the cases above another regression caused by f_pos locking is that now FUSE filesystems that implement open with FOPEN_NONSEEKABLE flag, can no longer implement bidirectional stream-like files - for the same reason as above e.g. read can deadlock write locking on file.f_pos in the kernel. FUSE's FOPEN_NONSEEKABLE was added in 2008 in a7c1b990f715 ("fuse: implement nonseekable open") to support OSSPD. OSSPD implements /dev/dsp in userspace with FOPEN_NONSEEKABLE flag, with corresponding read and write routines not depending on current position at all, and with both read and write being potentially blocking operations: See https://github.com/libfuse/osspd https://lwn.net/Articles/308445 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1406 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1438-L1477 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1479-L1510 Corresponding libfuse example/test also describes FOPEN_NONSEEKABLE as "somewhat pipe-like files ..." with read handler not using offset. However that test implements only read without write and cannot exercise the deadlock scenario: https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L124-L131 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L146-L163 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L209-L216 I've actually hit the read vs write deadlock for real while implementing my FUSE filesystem where there is /head/watch file, for which open creates separate bidirectional socket-like stream in between filesystem and its user with both read and write being later performed simultaneously. And there it is semantically not easy to split the stream into two separate read-only and write-only channels: https://lab.nexedi.com/kirr/wendelin.core/blob/f13aa600/wcfs/wcfs.go#L88-169 Let's fix this regression. The plan is: 1. We can't change nonseekable_open to include &~FMODE_ATOMIC_POS - doing so would break many in-kernel nonseekable_open users which actually use ppos in read/write handlers. 2. Add stream_open() to kernel to open stream-like non-seekable file descriptors. Read and write on such file descriptors would never use nor change ppos. And with that property on stream-like files read and write will be running without taking f_pos lock - i.e. read and write could be running simultaneously. 3. With semantic patch search and convert to stream_open all in-kernel nonseekable_open users for which read and write actually do not depend on ppos and where there is no other methods in file_operations which assume @offset access. 4. Add FOPEN_STREAM to fs/fuse/ and open in-kernel file-descriptors via steam_open if that bit is present in filesystem open reply. It was tempting to change fs/fuse/ open handler to use stream_open instead of nonseekable_open on just FOPEN_NONSEEKABLE flags, but grepping through Debian codesearch shows users of FOPEN_NONSEEKABLE, and in particular GVFS which actually uses offset in its read and write handlers https://codesearch.debian.net/search?q=-%3Enonseekable+%3D https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1080 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1247-1346 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1399-1481 so if we would do such a change it will break a real user. 5. Add stream_open and FOPEN_STREAM handling to stable kernels starting from v3.14+ (the kernel where 9c225f2655 first appeared). This will allow to patch OSSPD and other FUSE filesystems that provide stream-like files to return FOPEN_STREAM | FOPEN_NONSEEKABLE in their open handler and this way avoid the deadlock on all kernel versions. This should work because fs/fuse/ ignores unknown open flags returned from a filesystem and so passing FOPEN_STREAM to a kernel that is not aware of this flag cannot hurt. In turn the kernel that is not aware of FOPEN_STREAM will be < v3.14 where just FOPEN_NONSEEKABLE is sufficient to implement streams without read vs write deadlock. This patch adds stream_open, converts /proc/xen/xenbus to it and adds semantic patch to automatically locate in-kernel places that are either required to be converted due to read vs write deadlock, or that are just safe to be converted because read and write do not use ppos and there are no other funky methods in file_operations. Regarding semantic patch I've verified each generated change manually - that it is correct to convert - and each other nonseekable_open instance left - that it is either not correct to convert there, or that it is not converted due to current stream_open.cocci limitations. The script also does not convert files that should be valid to convert, but that currently have .llseek = noop_llseek or generic_file_llseek for unknown reason despite file being opened with nonseekable_open (e.g. drivers/input/mousedev.c) Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Yongzhi Pan <panyongzhi@gmail.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Juergen Gross <jgross@suse.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Tejun Heo <tj@kernel.org> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Christoph Hellwig <hch@lst.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Julia Lawall <Julia.Lawall@lip6.fr> Cc: Nikolaus Rath <Nikolaus@rath.org> Cc: Han-Wen Nienhuys <hanwen@google.com> Signed-off-by: Kirill Smelkov <kirr@nexedi.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-03-27 01:20:43 +03:00
filp->f_mode |= FMODE_STREAM;
return 0;
}
EXPORT_SYMBOL(stream_open);