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

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

From: Nathaniel Yazdani <redacted>

commit c338c07c51e3106711fad5eb599e375eadb6855d upstream.

When register_session() is given an out-of-range argument for mds,
ceph_mdsmap_get_addr() will return a null pointer, which would be given to
ceph_con_open() & be dereferenced, causing a kernel oops. This fixes bug #4685
in the Ceph bug tracker <http://tracker.ceph.com/issues/4685>.

Signed-off-by: Nathaniel Yazdani <redacted>
Reviewed-by: Sage Weil <redacted>
Signed-off-by: Luis Henriques <redacted>
---
 fs/ceph/mds_client.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 17b97ff..96d03db 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c

@@ -414,6 +414,9 @@ static struct ceph_mds_session *register_session(struct ceph_mds_client *mdsc,
 {
 	struct ceph_mds_session *s;
 
+	if (mds >= mdsc->mdsmap->m_max_mds)
+		return ERR_PTR(-EINVAL);
+
 	s = kzalloc(sizeof(*s), GFP_NOFS);
 	if (!s)
 		return ERR_PTR(-ENOMEM);

-- 
1.8.3.2