[TCP]: TCP_DEFER_ACCEPT updates - process as established

Change TCP_DEFER_ACCEPT implementation so that it transitions a
connection to ESTABLISHED after handshake is complete instead of
leaving it in SYN-RECV until some data arrvies. Place connection in
accept queue when first data packet arrives from slow path.

Benefits:
  - established connection is now reset if it never makes it
   to the accept queue

 - diagnostic state of established matches with the packet traces
   showing completed handshake

 - TCP_DEFER_ACCEPT timeouts are expressed in seconds and can now be
   enforced with reasonable accuracy instead of rounding up to next
   exponential back-off of syn-ack retry.

Signed-off-by: Patrick McManus <mcmanus@ducksong.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 46 insertions, 0 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 9cf4464..6e46b4c0 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4451,6 +4451,49 @@ static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
 	}
 }
 
+static int tcp_defer_accept_check(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	if (tp->defer_tcp_accept.request) {
+		int queued_data =  tp->rcv_nxt - tp->copied_seq;
+		int hasfin =  !skb_queue_empty(&sk->sk_receive_queue) ?
+			tcp_hdr((struct sk_buff *)
+				sk->sk_receive_queue.prev)->fin : 0;
+
+		if (queued_data && hasfin)
+			queued_data--;
+
+		if (queued_data &&
+		    tp->defer_tcp_accept.listen_sk->sk_state == TCP_LISTEN) {
+			if (sock_flag(sk, SOCK_KEEPOPEN)) {
+				inet_csk_reset_keepalive_timer(sk,
+							       keepalive_time_when(tp));
+			} else {
+				inet_csk_delete_keepalive_timer(sk);
+			}
+
+			inet_csk_reqsk_queue_add(
+				tp->defer_tcp_accept.listen_sk,
+				tp->defer_tcp_accept.request,
+				sk);
+
+			tp->defer_tcp_accept.listen_sk->sk_data_ready(
+				tp->defer_tcp_accept.listen_sk, 0);
+
+			sock_put(tp->defer_tcp_accept.listen_sk);
+			sock_put(sk);
+			tp->defer_tcp_accept.listen_sk = NULL;
+			tp->defer_tcp_accept.request = NULL;
+		} else if (hasfin ||
+			   tp->defer_tcp_accept.listen_sk->sk_state != TCP_LISTEN) {
+			tcp_reset(sk);
+			return -1;
+		}
+	}
+	return 0;
+}
+
 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
@@ -4811,6 +4854,9 @@ step5:
 
 	tcp_data_snd_check(sk);
 	tcp_ack_snd_check(sk);
+
+	if (tcp_defer_accept_check(sk))
+		return -1;
 	return 0;
 
 csum_error: