[PATCH 5.7 084/204] ceph: handle zero-length feature mask in session messages

Greg Kroah-Hartman
2020-08-20T13:07:35Z

From: Jeff Layton <jlayton@kernel.org>

commit 02e37571f9e79022498fd0525c073b07e9d9ac69 upstream.

Most session messages contain a feature mask, but the MDS will
routinely send a REJECT message with one that is zero-length.

Commit 0fa8263367db ("ceph: fix endianness bug when handling MDS
session feature bits") fixed the decoding of the feature mask,
but failed to account for the MDS sending a zero-length feature
mask. This causes REJECT message decoding to fail.

Skip trying to decode a feature mask if the word count is zero.

Cc: stable@vger.kernel.org
URL: https://tracker.ceph.com/issues/46823
Fixes: 0fa8263367db ("ceph: fix endianness bug when handling MDS session feature bits")
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Tested-by: Patrick Donnelly <pdonnell@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/ceph/mds_client.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -3270,8 +3270,10 @@ static void handle_session(struct ceph_m
goto bad;
/* version >= 3, feature bits */
ceph_decode_32_safe(&p, end, len, bad);
- ceph_decode_64_safe(&p, end, features, bad);
- p += len - sizeof(features);
+ if (len) {
+ ceph_decode_64_safe(&p, end, features, bad);
+ p += len - sizeof(features);
+ }
}

mutex_lock(&mdsc->mutex);