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

[Greg Kroah-Hartman]

From: Jeff Layton <jlayton@xxxxxxxxxx>

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@xxxxxxxxxxxxxxx
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@xxxxxxxxxx>
Reviewed-by: Ilya Dryomov <idryomov@xxxxxxxxx>
Tested-by: Patrick Donnelly <pdonnell@xxxxxxxxxx>
Signed-off-by: Ilya Dryomov <idryomov@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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);