3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Yan, Zheng" <redacted>

(cherry picked from commit 3e8f43a089f06279c5f76a9ccd42578eebf7bfa5)

When i >= newmap->m_max_mds, ceph_mdsmap_get_addr(newmap, i) return
NULL. Passing NULL to memcmp() triggers oops.

Signed-off-by: Yan, Zheng <redacted>
Signed-off-by: Sage Weil <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/ceph/mds_client.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c

@@ -2634,7 +2634,8 @@ static void check_new_map(struct ceph_md
 		     ceph_mdsmap_is_laggy(newmap, i) ? " (laggy)" : "",
 		     session_state_name(s->s_state));
 
-		if (memcmp(ceph_mdsmap_get_addr(oldmap, i),
+		if (i >= newmap->m_max_mds ||
+		    memcmp(ceph_mdsmap_get_addr(oldmap, i),
 			   ceph_mdsmap_get_addr(newmap, i),
 			   sizeof(struct ceph_entity_addr))) {
 			if (s->s_state == CEPH_MDS_SESSION_OPENING) {