mount: fix incorrect "success" exitcode if loop device setup fails

When mounting, in parallel, multiple loop devices (squashfs for the
submitter's case), the following behavior can be observed:

stat64(/path/to/image, {st_mode=S_IFREG|0644, st_size=4096, ...}) = 0
openat(AT_FDCWD, /path/to/image, O_RDWR|O_LARGEFILE) = 3
openat(AT_FDCWD, /dev/loop-control, O_RDWR|O_LARGEFILE|O_CLOEXEC) = 4
ioctl(4, LOOP_CTL_GET_FREE)             = 12
close(4)                                = 0
openat(AT_FDCWD, /dev/loop12, O_RDWR|O_LARGEFILE) = 4
ioctl(4, LOOP_GET_STATUS64, {lo_offset=0, lo_number=12, lo_flags=LO_FLAGS_AUTOCLEAR, lo_file_name=/path/to/image, ...}) = 0
close(4)                                = 0
close(3)                                = 0
write(2, "mount: can't setup loop device\n", 31mount: can't setup loop device
) = 31
exit_group(0)                           = ?
+++ exited with 0 +++

The ioctl LOOP_CTL_GET_FREE has resulted in the same result for
a competing mount process. The subsequent ioctl LOOP_GET_STATUS64
fails, having succeeded for the competing mount process.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/util-linux/mount.c b/util-linux/mount.c
index 2eadee88b..0814a5256 100644
--- a/util-linux/mount.c
+++ b/util-linux/mount.c
@@ -2078,8 +2078,8 @@ static int singlemount(struct mntent *mp, int ignore_busy)
          && (!mp->mnt_type || is_prefixed_with(mp->mnt_type, "nfs"))
         ) {
                 char *colon = strchr(mp->mnt_fsname, ':');
-                if (colon /* looks like "hostname:..." */
-                 && strchrnul(mp->mnt_fsname, '/') > colon /* "hostname:" has no slashes */
+                if (colon // looks like "hostname:..."
+                 && strchrnul(mp->mnt_fsname, '/') > colon // "hostname:" has no slashes
                 ) {
                         if (!mp->mnt_type)
                                 mp->mnt_type = (char*)"nfs";
@@ -2125,7 +2125,7 @@ static int singlemount(struct mntent *mp, int ignore_busy)
                                         bb_simple_error_msg(bb_msg_perm_denied_are_you_root);
                                 else
                                         bb_simple_perror_msg("can't setup loop device");
-                                return errno;
+                                return loopfd; // was "return errno", but it can be 0 here
                         }
 
                 // Autodetect bind mounts