Commit e3715899 authored Jul 17, 2012 by Eric Dumazet Committed by David S. Miller Jul 18, 2012

tcp: refine SYN handling in tcp_validate_incoming



Followup of commit 0c24604b (tcp: implement RFC 5961 4.2)

As reported by Vijay Subramanian, we should send a challenge ACK
instead of a dup ack if a SYN flag is set on a packet received out of
window.

This permits the ratelimiting to work as intended, and to increase
correct SNMP counters.

Suggested-by: Vijay Subramanian <subramanian.vijay@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Vijay Subramanian <subramanian.vijay@gmail.com>
Cc: Kiran Kumar Kella <kkiran@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent b6fe83e9

net/ipv4/tcp_input.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -5296,8 +5296,11 @@ static bool tcp_validate_incoming(struct sock sk, struct sk_buff skb,
		* an acknowledgment should be sent in reply (unless the RST
		* bit is set, if so drop the segment and return)".
		*/
		if (!th->rst)
		if (!th->rst) {
		if (th->syn)
		goto syn_challenge;
		tcp_send_dupack(sk, skb);
		}
		goto discard;
		}

		@@ -5327,6 +5330,7 @@ static bool tcp_validate_incoming(struct sock sk, struct sk_buff skb,
		* RFC 5691 4.2 : Send a challenge ack
		*/
		if (th->syn) {
		syn_challenge:
		if (syn_inerr)
		TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);