libceph: Fix NULL pointer dereference in auth client code

A malicious monitor can craft an auth reply message that could cause a
NULL function pointer dereference in the client's kernel.

To prevent this, the auth_none protocol handler needs an empty
ceph_auth_client_ops->build_request() function.

CVE-2013-1059
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Reported-by: Chanam Park <chanam.park@hkpco.kr>
Reviewed-by: Seth Arnold <seth.arnold@canonical.com>
Reviewed-by: Sage Weil <sage@inktank.com>
Cc: stable@vger.kernel.org

net/ceph/auth_none.c

@@ -39,6 +39,11 @@ static int should_authenticate(struct ceph_auth_client *ac)
 	return xi->starting;
 }
 
+static int build_request(struct ceph_auth_client *ac, void *buf, void *end)
+{
+	return 0;
+}
+
 /*
  * the generic auth code decode the global_id, and we carry no actual
  * authenticate state, so nothing happens here.
@@ -106,6 +111,7 @@ static const struct ceph_auth_client_ops ceph_auth_none_ops = {
 	.destroy = destroy,
 	.is_authenticated = is_authenticated,
 	.should_authenticate = should_authenticate,
+	.build_request = build_request,
 	.handle_reply = handle_reply,
 	.create_authorizer = ceph_auth_none_create_authorizer,
 	.destroy_authorizer = ceph_auth_none_destroy_authorizer,