rxrpc: Check address length before reading srx_service field

KMSAN will complain if valid address length passed to bind() is shorter
than sizeof(struct sockaddr_rxrpc) bytes.
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rxrpc/af_rxrpc.c

@@ -135,7 +135,7 @@ static int rxrpc_bind(struct socket *sock, struct sockaddr *saddr, int len)
 	struct sockaddr_rxrpc *srx = (struct sockaddr_rxrpc *)saddr;
 	struct rxrpc_local *local;
 	struct rxrpc_sock *rx = rxrpc_sk(sock->sk);
-	u16 service_id = srx->srx_service;
+	u16 service_id;
 	int ret;
 
 	_enter("%p,%p,%d", rx, saddr, len);
@@ -143,6 +143,7 @@ static int rxrpc_bind(struct socket *sock, struct sockaddr *saddr, int len)
 	ret = rxrpc_validate_address(rx, srx, len);
 	if (ret < 0)
 		goto error;
+	service_id = srx->srx_service;
 
 	lock_sock(&rx->sk);