tcp: fix __tcp_close() to only send RST when required

If the receive queue contains payload that was already
received, __tcp_close() can send an unexpected RST.

Refine the code to take tp->copied_seq into account,
as we already do in tcp recvmsg().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <[e-mail]>
Reviewed-by: Neal Cardwell <[e-mail]>
Reviewed-by: Kuniyuki Iwashima <[e-mail]>
Reviewed-by: Jason Xing <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/ipv4/tcp.c

···
 
 void __tcp_close(struct sock *sk, long timeout)
 {
+	bool data_was_unread = false;
 	struct sk_buff *skb;
-	int data_was_unread = 0;
 	int state;
 
 	WRITE_ONCE(sk->sk_shutdown, SHUTDOWN_MASK);
···
 	 *  reader process may not have drained the data yet!
 	 */
 	while ((skb = __skb_dequeue(&sk->sk_receive_queue)) != NULL) {
-		u32 len = TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq;
+		u32 end_seq = TCP_SKB_CB(skb)->end_seq;
 
 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
-			len--;
-		data_was_unread += len;
+			end_seq--;
+		if (after(end_seq, tcp_sk(sk)->copied_seq))
+			data_was_unread = true;
 		__kfree_skb(skb);
 	}