tcp: consume incoming skb leading to a reset

Whenever tcp_validate_incoming() handles a valid RST packet,
we should not pretend the packet was dropped.

Create a special section at the end of tcp_validate_incoming()
to handle this case.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -5700,7 +5700,7 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
 						  &tp->last_oow_ack_time))
 				tcp_send_dupack(sk, skb);
 		} else if (tcp_reset_check(sk, skb)) {
-			tcp_reset(sk, skb);
+			goto reset;
 		}
 		goto discard;
 	}
@@ -5736,17 +5736,16 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
 		}
 
 		if (rst_seq_match)
-			tcp_reset(sk, skb);
-		else {
-			/* Disable TFO if RST is out-of-order
-			 * and no data has been received
-			 * for current active TFO socket
-			 */
-			if (tp->syn_fastopen && !tp->data_segs_in &&
-			    sk->sk_state == TCP_ESTABLISHED)
-				tcp_fastopen_active_disable(sk);
-			tcp_send_challenge_ack(sk);
-		}
+			goto reset;
+
+		/* Disable TFO if RST is out-of-order
+		 * and no data has been received
+		 * for current active TFO socket
+		 */
+		if (tp->syn_fastopen && !tp->data_segs_in &&
+		    sk->sk_state == TCP_ESTABLISHED)
+			tcp_fastopen_active_disable(sk);
+		tcp_send_challenge_ack(sk);
 		goto discard;
 	}
 
@@ -5771,6 +5770,11 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
 discard:
 	tcp_drop(sk, skb);
 	return false;
+
+reset:
+	tcp_reset(sk, skb);
+	__kfree_skb(skb);
+	return false;
 }
 
 /*