tcp: do not mess with listener sk_wmem_alloc

When removing sk_refcnt manipulation on synflood, I missed that
using skb_set_owner_w() was racy, if sk->sk_wmem_alloc had already
transitioned to 0.

We should hold sk_refcnt instead, but this is a big deal under attack.
(Doing so increase performance from 3.2 Mpps to 3.8 Mpps only)

In this patch, I chose to not attach a socket to syncookies skb.

Performance is now 5 Mpps instead of 3.2 Mpps.

Following patch will remove last known false sharing in
tcp_rcv_state_process()

Fixes: 3b24d854cb35 ("tcp/dccp: do not touch listener sk_refcnt under synflood")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 3 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 983f04c11177..7ea7034af83f 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6327,7 +6327,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
         }
         if (fastopen_sk) {
                 af_ops->send_synack(fastopen_sk, dst, &fl, req,
-                                    &foc, false);
+                                    &foc, TCP_SYNACK_FASTOPEN);
                 /* Add the child socket directly into the accept queue */
                 inet_csk_reqsk_queue_add(sk, req, fastopen_sk);
                 sk->sk_data_ready(sk);
@@ -6337,8 +6337,9 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
                 tcp_rsk(req)->tfo_listener = false;
                 if (!want_cookie)
                         inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
-                af_ops->send_synack(sk, dst, &fl, req,
-                                    &foc, !want_cookie);
+                af_ops->send_synack(sk, dst, &fl, req, &foc,
+                                    !want_cookie ? TCP_SYNACK_NORMAL :
+                                                   TCP_SYNACK_COOKIE);
                 if (want_cookie) {
                         reqsk_free(req);
                         return 0;