libceph: handle an empty authorize reply

The authorize reply can be empty, for example when the ticket used to
build the authorizer is too old and TAG_BADAUTHORIZER is returned from
the service.  Calling ->verify_authorizer_reply() results in an attempt
to decrypt and validate (somewhat) random data in au->buf (most likely
the signature block from calc_signature()), which fails and ends up in
con_fault_finish() with !con->auth_retry.  The ticket isn't invalidated
and the connection is retried again and again until a new ticket is
obtained from the monitor:

  libceph: osd2 192.168.122.1:6809 bad authorize reply
  libceph: osd2 192.168.122.1:6809 bad authorize reply
  libceph: osd2 192.168.122.1:6809 bad authorize reply
  libceph: osd2 192.168.122.1:6809 bad authorize reply

Let TAG_BADAUTHORIZER handler kick in and increment con->auth_retry.

Cc: stable@vger.kernel.org
Fixes: 5c056fdc5b ("libceph: verify authorize reply on connect")
Link: https://tracker.ceph.com/issues/20164
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Sage Weil <sage@redhat.com>

net/ceph/messenger.c

@@ -2058,6 +2058,8 @@ static int process_connect(struct ceph_connection *con)
 	dout("process_connect on %p tag %d\n", con, (int)con->in_tag);
 
 	if (con->auth) {
+		int len = le32_to_cpu(con->in_reply.authorizer_len);
+
 		/*
 		 * Any connection that defines ->get_authorizer()
 		 * should also define ->add_authorizer_challenge() and
@@ -2067,8 +2069,7 @@ static int process_connect(struct ceph_connection *con)
 		 */
 		if (con->in_reply.tag == CEPH_MSGR_TAG_CHALLENGE_AUTHORIZER) {
 			ret = con->ops->add_authorizer_challenge(
-				    con, con->auth->authorizer_reply_buf,
+				    con, con->auth->authorizer_reply_buf, len);
-				    le32_to_cpu(con->in_reply.authorizer_len));
 			if (ret < 0)
 				return ret;
 
@@ -2078,12 +2079,14 @@ static int process_connect(struct ceph_connection *con)
 			return 0;
 		}
 
+		if (len) {
 			ret = con->ops->verify_authorizer_reply(con);
 			if (ret < 0) {
 				con->error_msg = "bad authorize reply";
 				return ret;
 			}
 		}
+	}
 
 	switch (con->in_reply.tag) {
 	case CEPH_MSGR_TAG_FEATURES: