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mount-util: add name_to_handle_at_loop() wrapper around name_to_handle_at()

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As it turns out MAX_HANDLE_SZ is a lie, the handle buffer we pass into
name_to_handle_at() might need to be larger than MAX_HANDLE_SZ, and we
thus need to invoke name_to_handle_at() in a loop, growing the buffer as
needed.

This adds a new wrapper name_to_handle_at_loop() around
name_to_handle_at() that does the necessary looping, and ports over all
users.

Fixes: #7082
This commit is contained in:
Lennart Poettering 2017-11-20 15:29:53 +01:00
parent 172378e01b
commit cbfb8679dd
4 changed files with 102 additions and 49 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

133
src/basic/mount-util.c
View File

@ -40,6 +40,76 @@
#include "string-util.h"
#include "strv.h"
int name_to_handle_at_loop(
int fd,
const char *path,
struct file_handle **ret_handle,
int *ret_mnt_id,
int flags) {
_cleanup_free_ struct file_handle *h;
size_t n = MAX_HANDLE_SZ;
/* We need to invoke name_to_handle_at() in a loop, given that it might return EOVERFLOW when the specified
* buffer is too small. Note that in contrast to what the docs might suggest, MAX_HANDLE_SZ is only good as a
* start value, it is not an upper bound on the buffer size required.
*
* This improves on raw name_to_handle_at() also in one other regard: ret_handle and ret_mnt_id can be passed
* as NULL if there's no interest in either. */
h = malloc0(offsetof(struct file_handle, f_handle) + n);
if (!h)
return -ENOMEM;
h->handle_bytes = n;
for (;;) {
int mnt_id = -1;
size_t m;
if (name_to_handle_at(fd, path, h, &mnt_id, flags) >= 0) {
if (ret_handle) {
*ret_handle = h;
h = NULL;
}
if (ret_mnt_id)
*ret_mnt_id = mnt_id;
return 0;
}
if (errno != EOVERFLOW)
return -errno;
if (!ret_handle && ret_mnt_id && mnt_id >= 0) {
/* As it appears, name_to_handle_at() fills in mnt_id even when it returns EOVERFLOW, but
* that's undocumented. Hence, let's make use of this if it appears to be filled in, and the
* caller was interested in only the mount ID an nothing else. */
*ret_mnt_id = mnt_id;
return 0;
}
/* The buffer was too small. Size the new buffer by what name_to_handle_at() returned, but make sure it
* is always larger than what we passed in before */
m = h->handle_bytes > n ? h->handle_bytes : n * 2;
if (m < n) /* Check for multiplication overflow */
return -EOVERFLOW;
if (offsetof(struct file_handle, f_handle) + m < m) /* check for addition overflow */
return -EOVERFLOW;
n = m;
free(h);
h = malloc0(offsetof(struct file_handle, f_handle) + n);
if (!h)
return -ENOMEM;
h->handle_bytes = n;
}
}
static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *mnt_id) {
char path[strlen("/proc/self/fdinfo/") + DECIMAL_STR_MAX(int)];
_cleanup_free_ char *fdinfo = NULL;
@ -79,7 +149,7 @@ static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *mnt_id
}
int fd_is_mount_point(int fd, const char *filename, int flags) {
union file_handle_union h = FILE_HANDLE_INIT, h_parent = FILE_HANDLE_INIT;
_cleanup_free_ struct file_handle *h = NULL, *h_parent = NULL;
int mount_id = -1, mount_id_parent = -1;
bool nosupp = false, check_st_dev = true;
struct stat a, b;
@ -111,39 +181,30 @@ int fd_is_mount_point(int fd, const char *filename, int flags) {
* subvolumes have different st_dev, even though they aren't
* real mounts of their own. */
r = name_to_handle_at(fd, filename, &h.handle, &mount_id, flags);
if (r < 0) {
if (IN_SET(errno, ENOSYS, EACCES, EPERM))
/* This kernel does not support name_to_handle_at() at all, or the syscall was blocked (maybe
* through seccomp, because we are running inside of a container?): fall back to simpler
* logic. */
goto fallback_fdinfo;
else if (errno == EOPNOTSUPP)
/* This kernel or file system does not support
* name_to_handle_at(), hence let's see if the
* upper fs supports it (in which case it is a
* mount point), otherwise fallback to the
* traditional stat() logic */
nosupp = true;
else
return -errno;
}
r = name_to_handle_at_loop(fd, filename, &h, &mount_id, flags);
if (IN_SET(r, -ENOSYS, -EACCES, -EPERM))
/* This kernel does not support name_to_handle_at() at all, or the syscall was blocked (maybe through
* seccomp, because we are running inside of a container?): fall back to simpler logic. */
goto fallback_fdinfo;
else if (r == -EOPNOTSUPP)
/* This kernel or file system does not support name_to_handle_at(), hence let's see if the upper fs
* supports it (in which case it is a mount point), otherwise fallback to the traditional stat()
* logic */
nosupp = true;
else if (r < 0)
return r;
r = name_to_handle_at(fd, "", &h_parent.handle, &mount_id_parent, AT_EMPTY_PATH);
if (r < 0) {
if (errno == EOPNOTSUPP) {
if (nosupp)
/* Neither parent nor child do name_to_handle_at()?
We have no choice but to fall back. */
goto fallback_fdinfo;
else
/* The parent can't do name_to_handle_at() but the
* directory we are interested in can?
* If so, it must be a mount point. */
return 1;
} else
return -errno;
}
r = name_to_handle_at_loop(fd, "", &h_parent, &mount_id_parent, AT_EMPTY_PATH);
if (r == -EOPNOTSUPP) {
if (nosupp)
/* Neither parent nor child do name_to_handle_at()? We have no choice but to fall back. */
goto fallback_fdinfo;
else
/* The parent can't do name_to_handle_at() but the directory we are interested in can? If so,
* it must be a mount point. */
return 1;
} else if (r < 0)
return r;
/* The parent can do name_to_handle_at() but the
* directory we are interested in can't? If so, it
@ -156,9 +217,9 @@ int fd_is_mount_point(int fd, const char *filename, int flags) {
* assume this is the root directory, which is a mount
* point. */
if (h.handle.handle_bytes == h_parent.handle.handle_bytes &&
h.handle.handle_type == h_parent.handle.handle_type &&
memcmp(h.handle.f_handle, h_parent.handle.f_handle, h.handle.handle_bytes) == 0)
if (h->handle_bytes == h_parent->handle_bytes &&
h->handle_type == h_parent->handle_type &&
memcmp(h->f_handle, h_parent->f_handle, h->handle_bytes) == 0)
return 1;
return mount_id != mount_id_parent;

9
src/basic/mount-util.h
View File

@ -30,6 +30,8 @@
#include "macro.h"
#include "missing.h"
int name_to_handle_at_loop(int fd, const char *path, struct file_handle **ret_handle, int *ret_mnt_id, int flags);
int fd_is_mount_point(int fd, const char *filename, int flags);
int path_is_mount_point(const char *path, const char *root, int flags);
@ -49,15 +51,8 @@ bool fstype_is_api_vfs(const char *fstype);
bool fstype_is_ro(const char *fsype);
bool fstype_can_discard(const char *fstype);
union file_handle_union {
struct file_handle handle;
char padding[sizeof(struct file_handle) + MAX_HANDLE_SZ];
};
const char* mode_to_inaccessible_node(mode_t mode);
#define FILE_HANDLE_INIT { .handle.handle_bytes = MAX_HANDLE_SZ }
int mount_verbose(
int error_log_level,
const char *what,

3
src/libudev/libudev-monitor.c
View File

@ -115,13 +115,12 @@ static struct udev_monitor *udev_monitor_new(struct udev *udev)
/* we consider udev running when /dev is on devtmpfs */
static bool udev_has_devtmpfs(struct udev *udev) {
union file_handle_union h = FILE_HANDLE_INIT;
_cleanup_fclose_ FILE *f = NULL;
char line[LINE_MAX], *e;
int mount_id;
int r;
r = name_to_handle_at(AT_FDCWD, "/dev", &h.handle, &mount_id, 0);
r = name_to_handle_at_loop(AT_FDCWD, "/dev", NULL, &mount_id, 0);
if (r < 0) {
if (errno != EOPNOTSUPP)
log_debug_errno(errno, "name_to_handle_at on /dev: %m");

6
src/tmpfiles/tmpfiles.c
View File

@ -346,16 +346,14 @@ static bool unix_socket_alive(const char *fn) {
static int dir_is_mount_point(DIR *d, const char *subdir) {
union file_handle_union h = FILE_HANDLE_INIT;
int mount_id_parent, mount_id;
int r_p, r;
r_p = name_to_handle_at(dirfd(d), ".", &h.handle, &mount_id_parent, 0);
r_p = name_to_handle_at_loop(dirfd(d), ".", NULL, &mount_id_parent, 0);
if (r_p < 0)
r_p = -errno;
h.handle.handle_bytes = MAX_HANDLE_SZ;
r = name_to_handle_at(dirfd(d), subdir, &h.handle, &mount_id, 0);
r = name_to_handle_at_loop(dirfd(d), subdir, NULL, &mount_id, 0);
if (r < 0)
r = -errno;