Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755480Ab0ARVUe (ORCPT ); Mon, 18 Jan 2010 16:20:34 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754835Ab0ARVUa (ORCPT ); Mon, 18 Jan 2010 16:20:30 -0500 Received: from proxima.lp0.eu ([81.2.80.65]:53845 "EHLO proxima.lp0.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755321Ab0ARVUY (ORCPT ); Mon, 18 Jan 2010 16:20:24 -0500 X-Greylist: delayed 682 seconds by postgrey-1.27 at vger.kernel.org; Mon, 18 Jan 2010 16:20:24 EST Message-ID: <4B54CDE5.3070100@simon.arlott.org.uk> Date: Mon, 18 Jan 2010 21:08:53 +0000 From: Simon Arlott User-Agent: Thunderbird 2.0.0.23 (X11/20090927) MIME-Version: 1.0 To: netdev , Patrick McHardy CC: Linux Kernel Mailing List Subject: [PATCH] xt_TCPMSS: SYN packets are allowed to contain data Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2491 Lines: 71 The check for data only needs to apply where the packet length could be increased by adding the MSS option. (The MSS option itself applies to the sender's maximum receive size which is not relevant to any data in its own packet.) This moves the check for (header size != packet size) to after attempting to modify an existing MSS option. Another check is needed before looking through the header to ensure it doesn't claim to be larger than the packet size. The ERROR level printk() is also removed as it can be triggered by remote hosts and is not useful: [4941777.937417] xt_TCPMSS: bad length (40 bytes) [4941782.409724] xt_TCPMSS: bad length (40 bytes) [4941790.762332] xt_TCPMSS: bad length (40 bytes) Signed-off-by: Simon Arlott --- net/netfilter/xt_TCPMSS.c | 21 +++++++++++---------- 1 files changed, 11 insertions(+), 10 deletions(-) diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c index eda64c1..76f92bf 100644 --- a/net/netfilter/xt_TCPMSS.c +++ b/net/netfilter/xt_TCPMSS.c @@ -60,17 +60,9 @@ tcpmss_mangle_packet(struct sk_buff *skb, tcplen = skb->len - tcphoff; tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff); - /* Since it passed flags test in tcp match, we know it is is - not a fragment, and has data >= tcp header length. SYN - packets should not contain data: if they did, then we risk - running over MTU, sending Frag Needed and breaking things - badly. --RR */ - if (tcplen != tcph->doff*4) { - if (net_ratelimit()) - printk(KERN_ERR "xt_TCPMSS: bad length (%u bytes)\n", - skb->len); + /* Header cannot be larger than the packet */ + if (tcplen < tcph->doff*4) return -1; - } if (info->mss == XT_TCPMSS_CLAMP_PMTU) { if (dst_mtu(skb_dst(skb)) <= minlen) { @@ -115,6 +107,15 @@ tcpmss_mangle_packet(struct sk_buff *skb, } } + /* Since it passed flags test in tcp match, we know it is + not a fragment, and has data >= tcp header length. SYN + packets should not contain data: if they did, then we risk + running over MTU, sending Frag Needed and breaking things + badly. --RR + */ + if (tcplen > tcph->doff*4) + return -1; + /* * MSS Option not found ?! add it.. */ -- 1.6.3.3 -- Simon Arlott -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/