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authorEric Dumazet <edumazet@google.com>2016-04-01 08:52:22 -0700
committerDavid S. Miller <davem@davemloft.net>2016-04-04 22:11:20 -0400
commit4ce7e93cb3fe87db5b700050172dc41def9834b3 (patch)
tree0a650d759c08cd171c4074553203b92f85e3fa29 /net/ipv4/tcp_minisocks.c
parenta9d6532b567489196dac4ce60c62343e43228759 (diff)
tcp: rate limit ACK sent by SYN_RECV request sockets
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>
Diffstat (limited to 'net/ipv4/tcp_minisocks.c')
-rw-r--r--net/ipv4/tcp_minisocks.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index acb366dd61e6..4c53e7c86586 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -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);