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, 7 insertions, 2 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 74d3ed5eb219..fd40f8c64d5f 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -452,10 +452,15 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
 int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb);
 int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
 int tcp_connect(struct sock *sk);
+enum tcp_synack_type {
+        TCP_SYNACK_NORMAL,
+        TCP_SYNACK_FASTOPEN,
+        TCP_SYNACK_COOKIE,
+};
 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
                                 struct request_sock *req,
                                 struct tcp_fastopen_cookie *foc,
-                                bool attach_req);
+                                enum tcp_synack_type synack_type);
 int tcp_disconnect(struct sock *sk, int flags);
 
 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb);
@@ -1728,7 +1733,7 @@ struct tcp_request_sock_ops {
         int (*send_synack)(const struct sock *sk, struct dst_entry *dst,
                            struct flowi *fl, struct request_sock *req,
                            struct tcp_fastopen_cookie *foc,
-                           bool attach_req);
+                           enum tcp_synack_type synack_type);
 };
 
 #ifdef CONFIG_SYN_COOKIES