tcp_input.c

					tcp_mtup_init(sk);
					tcp_init_buffer_space(sk);
					tp->copied_seq = tp->rcv_nxt;
				}
				smp_mb();
				tcp_set_state(sk, TCP_ESTABLISHED);
				sk->sk_state_change(sk);

				/* Note, that this wakeup is only for marginal
				 * crossed SYN case. Passively open sockets
				 * are not waked up, because sk->sk_sleep ==
				 * NULL and sk->sk_socket == NULL.
				 */
				if (sk->sk_socket)
					sk_wake_async(sk,
						      SOCK_WAKE_IO, POLL_OUT);

				tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
				tp->snd_wnd = ntohs(th->window) <<
					      tp->rx_opt.snd_wscale;
				tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);

				if (tp->rx_opt.tstamp_ok)
					tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;

				if (req) {
					/* Re-arm the timer because data may
					 * have been sent out. This is similar
					 * to the regular data transmission case
					 * when new data has just been ack'ed.
					 *
					 * (TFO) - we could try to be more
					 * aggressive and retranmitting any data
					 * sooner based on when they were sent
					 * out.
					 */
					tcp_rearm_rto(sk);
				} else
					tcp_init_metrics(sk);

				/* Prevent spurious tcp_cwnd_restart() on
				 * first data packet.
				 */
				tp->lsndtime = tcp_time_stamp;

				tcp_initialize_rcv_mss(sk);
				tcp_fast_path_on(tp);
			} else {
				return 1;
			}
			break;

		case TCP_FIN_WAIT1:
			/* If we enter the TCP_FIN_WAIT1 state and we are a
			 * Fast Open socket and this is the first acceptable
			 * ACK we have received, this would have acknowledged
			 * our SYNACK so stop the SYNACK timer.
			 */
			if (req != NULL) {
				/* Return RST if ack_seq is invalid.
				 * Note that RFC793 only says to generate a
				 * DUPACK for it but for TCP Fast Open it seems
				 * better to treat this case like TCP_SYN_RECV
				 * above.
				 */
				if (!acceptable)
					return 1;
				/* We no longer need the request sock. */
				reqsk_fastopen_remove(sk, req, false);
				tcp_rearm_rto(sk);
			}
			if (tp->snd_una == tp->write_seq) {
				struct dst_entry *dst;

				tcp_set_state(sk, TCP_FIN_WAIT2);
				sk->sk_shutdown |= SEND_SHUTDOWN;

				dst = __sk_dst_get(sk);
				if (dst)
					dst_confirm(dst);

				if (!sock_flag(sk, SOCK_DEAD))
					/* Wake up lingering close() */
					sk->sk_state_change(sk);
				else {
					int tmo;

					if (tp->linger2 < 0 ||
					    (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
					     after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
						tcp_done(sk);
						NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
						return 1;
					}

					tmo = tcp_fin_time(sk);
					if (tmo > TCP_TIMEWAIT_LEN) {
						inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
					} else if (th->fin || sock_owned_by_user(sk)) {
						/* Bad case. We could lose such FIN otherwise.
						 * It is not a big problem, but it looks confusing
						 * and not so rare event. We still can lose it now,
						 * if it spins in bh_lock_sock(), but it is really
						 * marginal case.
						 */
						inet_csk_reset_keepalive_timer(sk, tmo);
					} else {
						tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
						goto discard;
					}
				}
			}
			break;

		case TCP_CLOSING:
			if (tp->snd_una == tp->write_seq) {
				tcp_time_wait(sk, TCP_TIME_WAIT, 0);
				goto discard;
			}
			break;

		case TCP_LAST_ACK:
			if (tp->snd_una == tp->write_seq) {
				tcp_update_metrics(sk);
				tcp_done(sk);
				goto discard;
			}
			break;
		}
	} else
		goto discard;

	/* ts_recent update must be made after we are sure that the packet
	 * is in window.
	 */
	tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);

	/* step 6: check the URG bit */
	tcp_urg(sk, skb, th);

	/* step 7: process the segment text */
	switch (sk->sk_state) {
	case TCP_CLOSE_WAIT:
	case TCP_CLOSING:
	case TCP_LAST_ACK:
		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
			break;
	case TCP_FIN_WAIT1:
	case TCP_FIN_WAIT2:
		/* RFC 793 says to queue data in these states,
		 * RFC 1122 says we MUST send a reset.
		 * BSD 4.4 also does reset.
		 */
		if (sk->sk_shutdown & RCV_SHUTDOWN) {
			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
				NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
				tcp_reset(sk);
				return 1;
			}
		}
		/* Fall through */
	case TCP_ESTABLISHED:
		tcp_data_queue(sk, skb);
		queued = 1;
		break;
	}

	/* tcp_data could move socket to TIME-WAIT */
	if (sk->sk_state != TCP_CLOSE) {
		tcp_data_snd_check(sk);
		tcp_ack_snd_check(sk);
	}

	if (!queued) {
discard:
		__kfree_skb(skb);
	}
	return 0;
}
EXPORT_SYMBOL(tcp_rcv_state_process);