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machine: use file descriptor when chasing bind mount sources

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Allows to always operate on pinned inodes, rather than paths, so that
races are less likely
This commit is contained in:
Luca Boccassi 2021-01-15 15:50:45 +00:00
parent 98f654fdea
commit f7c18d3de8
1 changed files with 9 additions and 8 deletions
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17
src/shared/mount-util.c
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@ -757,12 +757,12 @@ int bind_mount_in_namespace(
bool make_file_or_directory) {
_cleanup_close_pair_ int errno_pipe_fd[2] = { -1, -1 };
_cleanup_close_ int self_mntns_fd = -1, mntns_fd = -1, root_fd = -1, pidns_fd = -1;
char mount_slave[] = "/tmp/propagate.XXXXXX", *mount_tmp, *mount_outside, *p;
_cleanup_close_ int self_mntns_fd = -1, mntns_fd = -1, root_fd = -1, pidns_fd = -1, chased_src_fd = -1;
char mount_slave[] = "/tmp/propagate.XXXXXX", *mount_tmp, *mount_outside, *p,
chased_src[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int)];
bool mount_slave_created = false, mount_slave_mounted = false,
mount_tmp_created = false, mount_tmp_mounted = false,
mount_outside_created = false, mount_outside_mounted = false;
_cleanup_free_ char *chased_src = NULL;
struct stat st, self_mntns_st;
pid_t child;
int r;
@ -800,14 +800,15 @@ int bind_mount_in_namespace(
if (r < 0)
return log_debug_errno(r == -ENOENT ? SYNTHETIC_ERRNO(EOPNOTSUPP) : r, "Target does not allow propagation of mount points");
r = chase_symlinks(src, NULL, CHASE_TRAIL_SLASH, &chased_src, NULL);
r = chase_symlinks(src, NULL, CHASE_TRAIL_SLASH, NULL, &chased_src_fd);
if (r < 0)
return log_debug_errno(r, "Failed to resolve source path of %s: %m", src);
xsprintf(chased_src, "/proc/self/fd/%i", chased_src_fd);
if (lstat(chased_src, &st) < 0)
return log_debug_errno(errno, "Failed to stat() resolved source path %s: %m", chased_src);
if (fstat(chased_src_fd, &st) < 0)
return log_debug_errno(errno, "Failed to stat() resolved source path %s: %m", src);
if (S_ISLNK(st.st_mode)) /* This shouldn't really happen, given that we just chased the symlinks above, but let's better be safe… */
return log_debug_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "Source directory %s can't be a symbolic link", chased_src);
return log_debug_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "Source directory %s can't be a symbolic link", src);
/* Our goal is to install a new bind mount into the container,
possibly read-only. This is irritatingly complex
@ -843,7 +844,7 @@ int bind_mount_in_namespace(
mount_tmp_created = true;
r = mount_nofollow_verbose(LOG_DEBUG, chased_src, mount_tmp, NULL, MS_BIND, NULL);
r = mount_follow_verbose(LOG_DEBUG, chased_src, mount_tmp, NULL, MS_BIND, NULL);
if (r < 0)
goto finish;