diff options
Diffstat (limited to 'src/basic/mountpoint-util.c')
| -rw-r--r-- | src/basic/mountpoint-util.c | 51 |
1 files changed, 32 insertions, 19 deletions
diff --git a/src/basic/mountpoint-util.c b/src/basic/mountpoint-util.c index bb6b6f064d..87cb5558f4 100644 --- a/src/basic/mountpoint-util.c +++ b/src/basic/mountpoint-util.c @@ -136,33 +136,46 @@ int fd_is_mount_point(int fd, const char *filename, int flags) { int mount_id = -1, mount_id_parent = -1; bool nosupp = false, check_st_dev = true; struct stat a, b; + struct statx sx +#if HAS_FEATURE_MEMORY_SANITIZER + = {} +# warning "Explicitly initializing struct statx, to work around msan limitation. Please remove as soon as msan has been updated to not require this." +#endif + ; int r; assert(fd >= 0); assert(filename); + assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0); - /* First we will try the name_to_handle_at() syscall, which - * tells us the mount id and an opaque file "handle". It is - * not supported everywhere though (kernel compile-time - * option, not all file systems are hooked up). If it works - * the mount id is usually good enough to tell us whether - * something is a mount point. + /* First we will try statx()' STATX_ATTR_MOUNT_ROOT attribute, which is our ideal API, available + * since kernel 5.8. + * + * If that fails, our second try is the name_to_handle_at() syscall, which tells us the mount id and + * an opaque file "handle". It is not supported everywhere though (kernel compile-time option, not + * all file systems are hooked up). If it works the mount id is usually good enough to tell us + * whether something is a mount point. * - * If that didn't work we will try to read the mount id from - * /proc/self/fdinfo/<fd>. This is almost as good as - * name_to_handle_at(), however, does not return the - * opaque file handle. The opaque file handle is pretty useful - * to detect the root directory, which we should always - * consider a mount point. Hence we use this only as - * fallback. Exporting the mnt_id in fdinfo is a pretty recent + * If that didn't work we will try to read the mount id from /proc/self/fdinfo/<fd>. This is almost + * as good as name_to_handle_at(), however, does not return the opaque file handle. The opaque file + * handle is pretty useful to detect the root directory, which we should always consider a mount + * point. Hence we use this only as fallback. Exporting the mnt_id in fdinfo is a pretty recent * kernel addition. * - * As last fallback we do traditional fstat() based st_dev - * comparisons. This is how things were traditionally done, - * but unionfs breaks this since it exposes file - * systems with a variety of st_dev reported. Also, btrfs - * subvolumes have different st_dev, even though they aren't - * real mounts of their own. */ + * As last fallback we do traditional fstat() based st_dev comparisons. This is how things were + * traditionally done, but unionfs breaks this since it exposes file systems with a variety of st_dev + * reported. Also, btrfs subvolumes have different st_dev, even though they aren't real mounts of + * their own. */ + + if (statx(fd, filename, (FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? 0 : AT_SYMLINK_NOFOLLOW) | + (flags & AT_EMPTY_PATH) | + AT_NO_AUTOMOUNT, 0, &sx) < 0) { + if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno)) + return -errno; + + /* If statx() is not available or forbidden, fallback to name_to_handle_at() below */ + } else if (FLAGS_SET(sx.stx_attributes_mask, STATX_ATTR_MOUNT_ROOT)) /* yay! */ + return FLAGS_SET(sx.stx_attributes, STATX_ATTR_MOUNT_ROOT); r = name_to_handle_at_loop(fd, filename, &h, &mount_id, flags); if (IN_SET(r, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL)) |