[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>

9 files changed, 99 insertions, 33 deletions

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 08027f1d7f31..d96d9b122304 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -239,6 +239,11 @@ static inline struct tcp_request_sock *tcp_rsk(const struct request_sock *req)
         return (struct tcp_request_sock *)req;
 }
 
+struct tcp_deferred_accept_info {
+        struct sock *listen_sk;
+        struct request_sock *request;
+};
+
 struct tcp_sock {
         /* inet_connection_sock has to be the first member of tcp_sock */
         struct inet_connection_sock     inet_conn;
@@ -374,6 +379,8 @@ struct tcp_sock {
         unsigned int            keepalive_intvl;  /* time interval between keep alive probes */
         int                     linger2;
 
+        struct tcp_deferred_accept_info defer_tcp_accept;
+
         unsigned long last_synq_overflow; 
 
         u32     tso_deferred;
diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index 040780add355..0369f98e9f3a 100644
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -115,8 +115,8 @@ struct request_sock_queue {
         struct request_sock     *rskq_accept_head;
         struct request_sock     *rskq_accept_tail;
         rwlock_t                syn_wait_lock;
-        u8                      rskq_defer_accept;
-        /* 3 bytes hole, try to pack */
+        u16                     rskq_defer_accept;
+        /* 2 bytes hole, try to pack */
         struct listen_sock      *listen_opt;
 };
 
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 847e1634e1f4..67cc3956d29c 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -139,6 +139,7 @@ extern void tcp_time_wait(struct sock *sk, int state, int timeo);
 #define MAX_TCP_KEEPINTVL       32767
 #define MAX_TCP_KEEPCNT         127
 #define MAX_TCP_SYNCNT          127
+#define MAX_TCP_ACCEPT_DEFERRED 65535
 
 #define TCP_SYNQ_INTERVAL       (HZ/5)  /* Period of SYNACK timer */
 
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 8a45be988709..cc1a1859a61b 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -414,8 +414,7 @@ void inet_csk_reqsk_queue_prune(struct sock *parent,
         struct inet_connection_sock *icsk = inet_csk(parent);
         struct request_sock_queue *queue = &icsk->icsk_accept_queue;
         struct listen_sock *lopt = queue->listen_opt;
-        int max_retries = icsk->icsk_syn_retries ? : sysctl_tcp_synack_retries;
-        int thresh = max_retries;
+        int thresh = icsk->icsk_syn_retries ? : sysctl_tcp_synack_retries;
         unsigned long now = jiffies;
         struct request_sock **reqp, *req;
         int i, budget;
@@ -451,9 +450,6 @@ void inet_csk_reqsk_queue_prune(struct sock *parent,
                 }
         }
 
-        if (queue->rskq_defer_accept)
-                max_retries = queue->rskq_defer_accept;
-
         budget = 2 * (lopt->nr_table_entries / (timeout / interval));
         i = lopt->clock_hand;
 
@@ -461,9 +457,8 @@ void inet_csk_reqsk_queue_prune(struct sock *parent,
                 reqp=&lopt->syn_table[i];
                 while ((req = *reqp) != NULL) {
                         if (time_after_eq(now, req->expires)) {
-                                if ((req->retrans < (inet_rsk(req)->acked ? max_retries : thresh)) &&
-                                    (inet_rsk(req)->acked ||
-                                     !req->rsk_ops->rtx_syn_ack(parent, req))) {
+                                if (req->retrans < thresh &&
+                                    !req->rsk_ops->rtx_syn_ack(parent, req)) {
                                         unsigned long timeo;
 
                                         if (req->retrans++ == 0)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 071e83a894ad..e0fbc25ca816 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2105,15 +2105,12 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
                 break;
 
         case TCP_DEFER_ACCEPT:
-                icsk->icsk_accept_queue.rskq_defer_accept = 0;
-                if (val > 0) {
-                        /* Translate value in seconds to number of
-                         * retransmits */
-                        while (icsk->icsk_accept_queue.rskq_defer_accept < 32 &&
-                               val > ((TCP_TIMEOUT_INIT / HZ) <<
-                                       icsk->icsk_accept_queue.rskq_defer_accept))
-                                icsk->icsk_accept_queue.rskq_defer_accept++;
-                        icsk->icsk_accept_queue.rskq_defer_accept++;
+                if (val < 0) {
+                        err = -EINVAL;
+                } else {
+                        if (val > MAX_TCP_ACCEPT_DEFERRED)
+                                val = MAX_TCP_ACCEPT_DEFERRED;
+                        icsk->icsk_accept_queue.rskq_defer_accept = val;
                 }
                 break;
 
@@ -2295,8 +2292,7 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
                         val = (val ? : sysctl_tcp_fin_timeout) / HZ;
                 break;
         case TCP_DEFER_ACCEPT:
-                val = !icsk->icsk_accept_queue.rskq_defer_accept ? 0 :
-                        ((TCP_TIMEOUT_INIT / HZ) << (icsk->icsk_accept_queue.rskq_defer_accept - 1));
+                val = icsk->icsk_accept_queue.rskq_defer_accept;
                 break;
         case TCP_WINDOW_CLAMP:
                 val = tp->window_clamp;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 9cf446427cc2..6e46b4c0f28c 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:
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 0ba6e911c979..167a0f557531 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1920,6 +1920,14 @@ int tcp_v4_destroy_sock(struct sock *sk)
                 sk->sk_sndmsg_page = NULL;
         }
 
+        if (tp->defer_tcp_accept.request) {
+                reqsk_free(tp->defer_tcp_accept.request);
+                sock_put(tp->defer_tcp_accept.listen_sk);
+                sock_put(sk);
+                tp->defer_tcp_accept.listen_sk = NULL;
+                tp->defer_tcp_accept.request = NULL;
+        }
+
         atomic_dec(&tcp_sockets_allocated);
 
         return 0;
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 8245247a6ceb..019c8c16e5cc 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:
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 803d758a2b12..160d16f9f4fc 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -481,6 +481,11 @@ static void tcp_keepalive_timer (unsigned long data)
                 goto death;
         }
 
+        if (tp->defer_tcp_accept.request && sk->sk_state == TCP_ESTABLISHED) {
+                tcp_send_active_reset(sk, GFP_ATOMIC);
+                goto death;
+        }
+
         if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
                 goto out;