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Commit 531c94a9 authored by Yuchung Cheng's avatar Yuchung Cheng Committed by David S. Miller
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tcp: don't include Fast Open option in SYN-ACK on pure SYN-data 



If a server has enabled Fast Open and it receives a pure SYN-data
packet (without a Fast Open option), it won't accept the data but it
incorrectly returns a SYN-ACK with a Fast Open cookie and also
increments the SNMP stat LINUX_MIB_TCPFASTOPENPASSIVEFAIL.

This patch makes the server include a Fast Open cookie in SYN-ACK
only if the SYN has some Fast Open option (i.e., when client
requests or presents a cookie).

Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 223ab8ff

net/ipv4/tcp_fastopen.c

+8 −5
Original line number Diff line number Diff line
@@ -255,6 +255,9 @@ bool tcp_try_fastopen(struct sock *sk, struct sk_buff *skb, 
	struct tcp_fastopen_cookie valid_foc = { .len = -1 };

	bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;



	if (foc->len == 0) /* Client requests a cookie */

		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);



	if (!((sysctl_tcp_fastopen & TFO_SERVER_ENABLE) &&

	      (syn_data || foc->len >= 0) &&

	      tcp_fastopen_queue_check(sk))) {
@@ -265,7 +268,8 @@ bool tcp_try_fastopen(struct sock *sk, struct sk_buff *skb, 
	if (syn_data && (sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_REQD))

		goto fastopen;



	if (tcp_fastopen_cookie_gen(req, skb, &valid_foc) &&

	if (foc->len >= 0 &&  /* Client presents or requests a cookie */

	    tcp_fastopen_cookie_gen(req, skb, &valid_foc) &&

	    foc->len == TCP_FASTOPEN_COOKIE_SIZE &&

	    foc->len == valid_foc.len &&

	    !memcmp(foc->val, valid_foc.val, foc->len)) {
@@ -284,11 +288,10 @@ bool tcp_try_fastopen(struct sock *sk, struct sk_buff *skb, 
					 LINUX_MIB_TCPFASTOPENPASSIVE);

			return true;

		}

	}

		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);

	} else if (foc->len > 0) /* Client presents an invalid cookie */

		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);



	NET_INC_STATS_BH(sock_net(sk), foc->len ?

			 LINUX_MIB_TCPFASTOPENPASSIVEFAIL :

			 LINUX_MIB_TCPFASTOPENCOOKIEREQD);

	*foc = valid_foc;

	return false;

}