ceph: fix null pointer dereference

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 <n1ght.4nd.d4y@gmail.com>
Reviewed-by: Sage Weil <sage@inktank.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 3eb1b4470c85..6b40d8112c64 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);