From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: [PATCH] rps: tcp: fix rps_sock_flow_table table updates Date: Thu, 03 Jun 2010 21:03:58 +0200 Message-ID: <1275591838.2533.37.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev To: Tom Herbert , David Miller Return-path: Received: from mail-ww0-f46.google.com ([74.125.82.46]:45309 "EHLO mail-ww0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751646Ab0FCTEF (ORCPT ); Thu, 3 Jun 2010 15:04:05 -0400 Received: by wwb28 with SMTP id 28so335064wwb.19 for ; Thu, 03 Jun 2010 12:04:01 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: I believe a moderate SYN flood attack can corrupt RFS flow table (rps_sock_flow_table), making RPS/RFS much less effective. Even in a normal situation, server handling short lived sessions suffer from bad steering for the first data packet of a session, if another SYN packet is received for another session. We do following action in tcp_v4_rcv() : sock_rps_save_rxhash(sk, skb->rxhash); We should _not_ do this if sk is a LISTEN socket, as about each packet received on a LISTEN socket has a different rxhash than previous one. -> RPS_NO_CPU markers are spread all over rps_sock_flow_table. Also, it makes sense to protect sk->rxhash field changes with socket lock (We currently can change it even if user thread owns the lock and might use rxhash) This patch moves sock_rps_save_rxhash() to a sock locked section, and only for non LISTEN sockets. Signed-off-by: Eric Dumazet --- net/ipv4/tcp_ipv4.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 202cf09..fe193e5 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1555,6 +1555,7 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb) #endif if (sk->sk_state == TCP_ESTABLISHED) { /* Fast path */ + sock_rps_save_rxhash(sk, skb->rxhash); TCP_CHECK_TIMER(sk); if (tcp_rcv_established(sk, skb, tcp_hdr(skb), skb->len)) { rsk = sk; @@ -1579,7 +1580,9 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb) } return 0; } - } + } else + sock_rps_save_rxhash(sk, skb->rxhash); + TCP_CHECK_TIMER(sk); if (tcp_rcv_state_process(sk, skb, tcp_hdr(skb), skb->len)) { @@ -1672,8 +1675,6 @@ process: skb->dev = NULL; - sock_rps_save_rxhash(sk, skb->rxhash); - bh_lock_sock_nested(sk); ret = 0; if (!sock_owned_by_user(sk)) {