linux-kernel - [PATCH 5.8 096/232] ceph: handle zero-length feature mask in session messages

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Date:   Thu, 20 Aug 2020 11:19:07 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jeff Layton <jlayton@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Patrick Donnelly <pdonnell@...hat.com>
Subject: [PATCH 5.8 096/232] ceph: handle zero-length feature mask in session messages

From: Jeff Layton <jlayton@...nel.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@...r.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@...nel.org>
Reviewed-by: Ilya Dryomov <idryomov@...il.com>
Tested-by: Patrick Donnelly <pdonnell@...hat.com>
Signed-off-by: Ilya Dryomov <idryomov@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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
@@ -3279,8 +3279,10 @@ 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);