tipc: fix socket flow control accounting error at tipc_recv_stream

Until now in tipc_recv_stream(), we update the received
unacknowledged bytes based on a stack variable and not based on the
actual message size.
If the user buffer passed at tipc_recv_stream() is smaller than the
received skb, the size variable in stack differs from the actual
message size in the skb. This leads to a flow control accounting
error causing permanent congestion.

In this commit, we fix this accounting error by always using the
size of the incoming message.

Fixes: 10724cc7 ("tipc: redesign connection-level flow control")
Signed-off-by: NParthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>
Reviewed-by: NJon Maloy <jon.maloy@ericsson.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/tipc/socket.c

@@ -1484,7 +1484,7 @@ static int tipc_recv_stream(struct socket *sock, struct msghdr *m,
 	if (unlikely(flags & MSG_PEEK))
 		goto exit;
 
-	tsk->rcv_unacked += tsk_inc(tsk, hlen + sz);
+	tsk->rcv_unacked += tsk_inc(tsk, hlen + msg_data_sz(msg));
 	if (unlikely(tsk->rcv_unacked >= (tsk->rcv_win / 4)))
 		tipc_sk_send_ack(tsk);
 	tsk_advance_rx_queue(sk);