tcp: TCP Fast Open Server - support TFO listeners

This patch builds on top of the previous patch to add the support
for TFO listeners. This includes -

1. allocating, properly initializing, and managing the per listener
fastopen_queue structure when TFO is enabled

2. changes to the inet_csk_accept code to support TFO. E.g., the
request_sock can no longer be freed upon accept(), not until 3WHS
finishes

3. allowing a TCP_SYN_RECV socket to properly poll() and sendmsg()
if it's a TFO socket

4. properly closing a TFO listener, and a TFO socket before 3WHS
finishes

5. supporting TCP_FASTOPEN socket option

6. modifying tcp_check_req() to use to check a TFO socket as well
as request_sock

7. supporting TCP's TFO cookie option

8. adding a new SYN-ACK retransmit handler to use the timer directly
off the TFO socket rather than the listener socket. Note that TFO
server side will not retransmit anything other than SYN-ACK until
the 3WHS is completed.

The patch also contains an important function
"reqsk_fastopen_remove()" to manage the somewhat complex relation
between a listener, its request_sock, and the corresponding child
socket. See the comment above the function for the detail.

Signed-off-by: H.K. Jerry Chu <hkchu@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 27 insertions, 1 deletions

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 6681ccf5c3ee..4f70ef0b946d 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -149,6 +149,11 @@ void inet_sock_destruct(struct sock *sk)
 		pr_err("Attempt to release alive inet socket %p\n", sk);
 		return;
 	}
+	if (sk->sk_type == SOCK_STREAM) {
+		struct fastopen_queue *fastopenq =
+			inet_csk(sk)->icsk_accept_queue.fastopenq;
+		kfree(fastopenq);
+	}
 
 	WARN_ON(atomic_read(&sk->sk_rmem_alloc));
 	WARN_ON(atomic_read(&sk->sk_wmem_alloc));
@@ -212,6 +217,26 @@ int inet_listen(struct socket *sock, int backlog)
 	 * we can only allow the backlog to be adjusted.
 	 */
 	if (old_state != TCP_LISTEN) {
+		/* Check special setups for testing purpose to enable TFO w/o
+		 * requiring TCP_FASTOPEN sockopt.
+		 * Note that only TCP sockets (SOCK_STREAM) will reach here.
+		 * Also fastopenq may already been allocated because this
+		 * socket was in TCP_LISTEN state previously but was
+		 * shutdown() (rather than close()).
+		 */
+		if ((sysctl_tcp_fastopen & TFO_SERVER_ENABLE) != 0 &&
+		    inet_csk(sk)->icsk_accept_queue.fastopenq == NULL) {
+			if ((sysctl_tcp_fastopen & TFO_SERVER_WO_SOCKOPT1) != 0)
+				err = fastopen_init_queue(sk, backlog);
+			else if ((sysctl_tcp_fastopen &
+				  TFO_SERVER_WO_SOCKOPT2) != 0)
+				err = fastopen_init_queue(sk,
+				    ((uint)sysctl_tcp_fastopen) >> 16);
+			else
+				err = 0;
+			if (err)
+				goto out;
+		}
 		err = inet_csk_listen_start(sk, backlog);
 		if (err)
 			goto out;
@@ -701,7 +726,8 @@ int inet_accept(struct socket *sock, struct socket *newsock, int flags)
 
 	sock_rps_record_flow(sk2);
 	WARN_ON(!((1 << sk2->sk_state) &
-		  (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT | TCPF_CLOSE)));
+		  (TCPF_ESTABLISHED | TCPF_SYN_RECV |
+		  TCPF_CLOSE_WAIT | TCPF_CLOSE)));
 
 	sock_graft(sk2, newsock);