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fanotify: enable FAN_REPORT_FID init flag

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When setting up an fanotify listener, user may request to get fid
information in event instead of an open file descriptor.

The fid obtained with event on a watched object contains the file
handle returned by name_to_handle_at(2) and fsid returned by statfs(2).

Restrict FAN_REPORT_FID to class FAN_CLASS_NOTIF, because we have have
no good reason to support reporting fid on permission events.

When setting a mark, we need to make sure that the filesystem
supports encoding file handles with name_to_handle_at(2) and that
statfs(2) encodes a non-zero fsid.

Cc: <linux-api@vger.kernel.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Amir Goldstein 2019-01-10 19:04:36 +02:00 committed by Jan Kara
parent 5e469c830f
commit a8b13aa20a
2 changed files with 61 additions and 2 deletions
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61
fs/notify/fanotify/fanotify_user.c
View File

@ -17,6 +17,8 @@
#include <linux/compat.h>
#include <linux/sched/signal.h>
#include <linux/memcontrol.h>
#include <linux/statfs.h>
#include <linux/exportfs.h>
#include <asm/ioctls.h>
@ -768,6 +770,10 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
return -EINVAL;
}
if ((flags & FAN_REPORT_FID) &&
(flags & FANOTIFY_CLASS_BITS) != FAN_CLASS_NOTIF)
return -EINVAL;
user = get_current_user();
if (atomic_read(&user->fanotify_listeners) > FANOTIFY_DEFAULT_MAX_LISTENERS) {
free_uid(user);
@ -854,6 +860,52 @@ out_destroy_group:
return fd;
}
/* Check if filesystem can encode a unique fid */
static int fanotify_test_fid(struct path *path)
{
struct kstatfs stat, root_stat;
struct path root = {
.mnt = path->mnt,
.dentry = path->dentry->d_sb->s_root,
};
int err;
/*
* Make sure path is not in filesystem with zero fsid (e.g. tmpfs).
*/
err = vfs_statfs(path, &stat);
if (err)
return err;
if (!stat.f_fsid.val[0] && !stat.f_fsid.val[1])
return -ENODEV;
/*
* Make sure path is not inside a filesystem subvolume (e.g. btrfs)
* which uses a different fsid than sb root.
*/
err = vfs_statfs(&root, &root_stat);
if (err)
return err;
if (root_stat.f_fsid.val[0] != stat.f_fsid.val[0] ||
root_stat.f_fsid.val[1] != stat.f_fsid.val[1])
return -EXDEV;
/*
* We need to make sure that the file system supports at least
* encoding a file handle so user can use name_to_handle_at() to
* compare fid returned with event to the file handle of watched
* objects. However, name_to_handle_at() requires that the
* filesystem also supports decoding file handles.
*/
if (!path->dentry->d_sb->s_export_op ||
!path->dentry->d_sb->s_export_op->fh_to_dentry)
return -EOPNOTSUPP;
return 0;
}
static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
int dfd, const char __user *pathname)
{
@ -939,6 +991,12 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
if (ret)
goto fput_and_out;
if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
ret = fanotify_test_fid(&path);
if (ret)
goto path_put_and_out;
}
/* inode held in place by reference to path; group by fget on fd */
if (mark_type == FAN_MARK_INODE)
inode = path.dentry->d_inode;
@ -967,6 +1025,7 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
ret = -EINVAL;
}
path_put_and_out:
path_put(&path);
fput_and_out:
fdput(f);
@ -1003,7 +1062,7 @@ COMPAT_SYSCALL_DEFINE6(fanotify_mark,
*/
static int __init fanotify_user_setup(void)
{
BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 7);
BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 8);
BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 9);
fanotify_mark_cache = KMEM_CACHE(fsnotify_mark,

2
include/linux/fanotify.h
View File

@ -19,7 +19,7 @@
FAN_CLASS_PRE_CONTENT)
#define FANOTIFY_INIT_FLAGS (FANOTIFY_CLASS_BITS | \
FAN_REPORT_TID | \
FAN_REPORT_TID | FAN_REPORT_FID | \
FAN_CLOEXEC | FAN_NONBLOCK | \
FAN_UNLIMITED_QUEUE | FAN_UNLIMITED_MARKS)