libceph: verify authorize reply on connect

After sending an authorizer (ceph_x_authorize_a + ceph_x_authorize_b),
the client gets back a ceph_x_authorize_reply, which it is supposed to
verify to ensure the authenticity and protect against replay attacks.
The code for doing this is there (ceph_x_verify_authorizer_reply(),
ceph_auth_verify_authorizer_reply() + plumbing), but it is never
invoked by the the messenger.

AFAICT this goes back to 2009, when ceph authentication protocols
support was added to the kernel client in 4e7a5dcd ("ceph:
negotiate authentication protocol; implement AUTH_NONE protocol").

The second param of ceph_connection_operations::verify_authorizer_reply
is unused all the way down.  Pass 0 to facilitate backporting, and kill
it in the next commit.

Cc: stable@vger.kernel.org
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Sage Weil <sage@redhat.com>

net/ceph/messenger.c

@@ -2027,6 +2027,19 @@ static int process_connect(struct ceph_connection *con)
 
 	dout("process_connect on %p tag %d\n", con, (int)con->in_tag);
 
+	if (con->auth_reply_buf) {
+		/*
+		 * Any connection that defines ->get_authorizer()
+		 * should also define ->verify_authorizer_reply().
+		 * See get_connect_authorizer().
+		 */
+		ret = con->ops->verify_authorizer_reply(con, 0);
+		if (ret < 0) {
+			con->error_msg = "bad authorize reply";
+			return ret;
+		}
+	}
+
 	switch (con->in_reply.tag) {
 	case CEPH_MSGR_TAG_FEATURES:
 		pr_err("%s%lld %s feature set mismatch,"