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Commit 10a19939 authored by Simon Arlott's avatar Simon Arlott Committed by Patrick McHardy
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netfilter: xt_TCPMSS: SYN packets are allowed to contain data 



The TCPMSS target is dropping SYN packets where:
  1) There is data, or
  2) The data offset makes the TCP header larger than the packet.

Both of these result in an error level printk. This printk has been
removed.

This change avoids dropping SYN packets containing data. If there
is also no MSS option (as well as data), one will not be added
because of possible complications due to the increased packet size.

Signed-off-by: default avatarSimon Arlott <simon@fire.lp0.eu>
Signed-off-by: default avatarPatrick McHardy <kaber@trash.net>
parent c30f540b

net/netfilter/xt_TCPMSS.c

+8 −10
Original line number Diff line number Diff line
@@ -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 +107,12 @@ tcpmss_mangle_packet(struct sk_buff *skb, 
		}

	}



	/* There is data after the header so the option can't be added

	   without moving it, and doing so may make the SYN packet

	   itself too large. Accept the packet unmodified instead. */

	if (tcplen > tcph->doff*4)

		return 0;



	/*

	 * MSS Option not found ?! add it..

	 */