[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, 20 insertions, 12 deletions

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 8245247a6ce..019c8c16e5c 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -571,10 +571,8 @@ struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb,
            does sequence test, SYN is truncated, and thus we consider
            it a bare ACK.
 
-           If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
-           bare ACK.  Otherwise, we create an established connection.  Both
-           ends (listening sockets) accept the new incoming connection and try
-           to talk to each other. 8-)
+           Both ends (listening sockets) accept the new incoming
+           connection and try to talk to each other. 8-)
 
            Note: This case is both harmless, and rare.  Possibility is about the
            same as us discovering intelligent life on another plant tomorrow.
@@ -642,13 +640,6 @@ struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb,
                 if (!(flg & TCP_FLAG_ACK))
                         return NULL;
 
-                /* If TCP_DEFER_ACCEPT is set, drop bare ACK. */
-                if (inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
-                    TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
-                        inet_rsk(req)->acked = 1;
-                        return NULL;
-                }
-
                 /* OK, ACK is valid, create big socket and
                  * feed this segment to it. It will repeat all
                  * the tests. THIS SEGMENT MUST MOVE SOCKET TO
@@ -687,7 +678,24 @@ struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb,
                 inet_csk_reqsk_queue_unlink(sk, req, prev);
                 inet_csk_reqsk_queue_removed(sk, req);
 
-                inet_csk_reqsk_queue_add(sk, req, child);
+                if (inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
+                    TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
+
+                        /* the accept queue handling is done is est recv slow
+                         * path so lets make sure to start there
+                         */
+                        tcp_sk(child)->pred_flags = 0;
+                        sock_hold(sk);
+                        sock_hold(child);
+                        tcp_sk(child)->defer_tcp_accept.listen_sk = sk;
+                        tcp_sk(child)->defer_tcp_accept.request = req;
+
+                        inet_csk_reset_keepalive_timer(child,
+                                                       inet_csk(sk)->icsk_accept_queue.rskq_defer_accept * HZ);
+                } else {
+                        inet_csk_reqsk_queue_add(sk, req, child);
+                }
+
                 return child;
 
         listen_overflow: