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tcp: refine SYN handling in tcp_validate_incoming 

Followup of commit 0c24604b68 (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>
This commit is contained in:
Eric Dumazet 2012-07-17 12:29:30 +00:00 committed by David S. Miller
parent b6fe83e952
commit e371589917
1 changed files with 5 additions and 1 deletions
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6
net/ipv4/tcp_input.c
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@ -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);