[PATCH 1/1] loop device: report mount failure in case of set_loop failure
Thomas De Schampheleire
patrickdepinguin at gmail.com
Mon May 18 12:03:11 UTC 2020
From: Philippe Belet <philippe.belet at nokia.com>
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. Next we
see a series of other system calls.
The mount code checks the errno value of the last close()
syscall, resulting in exit code 0 for the process, despite
mount failure.
Signed-off-by: Philippe Belet <philippe.belet at nokia.com>
Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire at nokia.com>
---
libbb/loop.c | 2 +-
util-linux/mount.c | 4 ++--
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/libbb/loop.c b/libbb/loop.c
index ada0c7638..23799e633 100644
--- a/libbb/loop.c
+++ b/libbb/loop.c
@@ -204,7 +204,7 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
}
}
} else {
- rc = -1;
+ rc = errno ? -errno : -EBUSY;
}
if (rc != 0) {
close(dfd);
diff --git a/util-linux/mount.c b/util-linux/mount.c
index 84c85c057..93b5ebac2 100644
--- a/util-linux/mount.c
+++ b/util-linux/mount.c
@@ -2046,11 +2046,11 @@ static int singlemount(struct mntent *mp, int ignore_busy)
| BB_LO_FLAGS_AUTOCLEAR
);
if (loopfd < 0) {
- if (errno == EPERM || errno == EACCES)
+ if (loopfd == -EPERM || loopfd == -EACCES)
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;
}
// Autodetect bind mounts
--
2.26.2
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