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tcp: rate limit ACK sent by SYN_RECV request sockets

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Attackers like to use SYNFLOOD targeting one 5-tuple, as they
hit a single RX queue (and cpu) on the victim.

If they use random sequence numbers in their SYN, we detect
they do not match the expected window and send back an ACK.

This patch adds a rate limitation, so that the effect of such
attacks is limited to ingress only.

We roughly double our ability to absorb such attacks.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Maciej Żenczykowski <maze@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2016-04-01 08:52:22 -07:00 committed by David S. Miller
parent a9d6532b56
commit 4ce7e93cb3
1 changed files with 4 additions and 1 deletions
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5
net/ipv4/tcp_minisocks.c
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@ -704,7 +704,10 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) {
/* Out of window: send ACK and drop. */
if (!(flg & TCP_FLAG_RST))
if (!(flg & TCP_FLAG_RST) &&
!tcp_oow_rate_limited(sock_net(sk), skb,
LINUX_MIB_TCPACKSKIPPEDSYNRECV,
&tcp_rsk(req)->last_oow_ack_time))
req->rsk_ops->send_ack(sk, skb, req);
if (paws_reject)
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);