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>

2 files changed, 4 insertions, 2 deletions

diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index bb46061c813a..182ab9a85d6c 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -190,6 +190,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
         ireq = inet_rsk(req);
         ireq6 = inet6_rsk(req);
         treq = tcp_rsk(req);
+        treq->listener = NULL;
 
         if (security_inet_conn_request(sk, skb, req))
                 goto out_free;
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index f99b81d53cca..09078b9bc6f6 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -475,7 +475,7 @@ static int tcp_v6_send_synack(struct sock *sk, struct dst_entry *dst,
         if (!dst && (dst = inet6_csk_route_req(sk, fl6, req)) == NULL)
                 goto done;
 
-        skb = tcp_make_synack(sk, dst, req, rvp);
+        skb = tcp_make_synack(sk, dst, req, rvp, NULL);
 
         if (skb) {
                 __tcp_v6_send_check(skb, &treq->loc_addr, &treq->rmt_addr);
@@ -987,7 +987,7 @@ static struct sock *tcp_v6_hnd_req(struct sock *sk,struct sk_buff *skb)
                                    &ipv6_hdr(skb)->saddr,
                                    &ipv6_hdr(skb)->daddr, inet6_iif(skb));
         if (req)
-                return tcp_check_req(sk, skb, req, prev);
+                return tcp_check_req(sk, skb, req, prev, false);
 
         nsk = __inet6_lookup_established(sock_net(sk), &tcp_hashinfo,
                         &ipv6_hdr(skb)->saddr, th->source,
@@ -1179,6 +1179,7 @@ have_isn:
             want_cookie)
                 goto drop_and_free;
 
+        tcp_rsk(req)->listener = NULL;
         inet6_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
         return 0;