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[3.5.y.z,extended,stable] Patch "netfilter: xt_TCPMSS: Fix IPv6 default MSS too" has been added to staging queue

Message ID 1373022152-25078-1-git-send-email-luis.henriques@canonical.com
State New
Headers show

Commit Message

Luis Henriques July 5, 2013, 11:02 a.m. UTC 
This is a note to let you know that I have just added a patch titled

    netfilter: xt_TCPMSS: Fix IPv6 default MSS too

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

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From abc3445bf9773a865beea9b0e0ffec96dc9ef836 Mon Sep 17 00:00:00 2001
From: Phil Oester <kernel@linuxace.com>
Date: Wed, 12 Jun 2013 10:44:51 +0200
Subject: [PATCH] netfilter: xt_TCPMSS: Fix IPv6 default MSS too

commit 70d19f805f8c047fc0a28dec9306b3773971c8d9 upstream.

As a followup to commit 409b545a ("netfilter: xt_TCPMSS: Fix violation
of RFC879 in absence of MSS option"), John Heffner points out that IPv6
has a higher MTU than IPv4, and thus a higher minimum MSS. Update TCPMSS
target to account for this, and update RFC comment.

While at it, point to more recent reference RFC1122 instead of RFC879.

Signed-off-by: Phil Oester <kernel@linuxace.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 net/netfilter/xt_TCPMSS.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

--
1.8.1.2
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Patch

diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index a77d786..cc2b572 100644
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -44,11 +44,12 @@  optlen(const u_int8_t *opt, unsigned int offset)

 static int
 tcpmss_mangle_packet(struct sk_buff *skb,
-		     const struct xt_tcpmss_info *info,
+		     const struct xt_action_param *par,
 		     unsigned int in_mtu,
 		     unsigned int tcphoff,
 		     unsigned int minlen)
 {
+	const struct xt_tcpmss_info *info = par->targinfo;
 	struct tcphdr *tcph;
 	unsigned int tcplen, i;
 	__be16 oldval;
@@ -128,11 +129,17 @@  tcpmss_mangle_packet(struct sk_buff *skb,

 	skb_put(skb, TCPOLEN_MSS);

-	/* RFC 879 states that the default MSS is 536 without specific
-	 * knowledge that the destination host is prepared to accept larger.
-	 * Since no MSS was provided, we MUST NOT set a value > 536.
+	/*
+	 * IPv4: RFC 1122 states "If an MSS option is not received at
+	 * connection setup, TCP MUST assume a default send MSS of 536".
+	 * IPv6: RFC 2460 states IPv6 has a minimum MTU of 1280 and a minimum
+	 * length IPv6 header of 60, ergo the default MSS value is 1220
+	 * Since no MSS was provided, we must use the default values
 	 */
-	newmss = min(newmss, (u16)536);
+	if (par->family == NFPROTO_IPV4)
+		newmss = min(newmss, (u16)536);
+	else
+		newmss = min(newmss, (u16)1220);

 	opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
 	memmove(opt + TCPOLEN_MSS, opt, tcplen - sizeof(struct tcphdr));
@@ -191,7 +198,7 @@  tcpmss_tg4(struct sk_buff *skb, const struct xt_action_param *par)
 	__be16 newlen;
 	int ret;

-	ret = tcpmss_mangle_packet(skb, par->targinfo,
+	ret = tcpmss_mangle_packet(skb, par,
 				   tcpmss_reverse_mtu(skb, PF_INET),
 				   iph->ihl * 4,
 				   sizeof(*iph) + sizeof(struct tcphdr));
@@ -220,7 +227,7 @@  tcpmss_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 	tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr, &frag_off);
 	if (tcphoff < 0)
 		return NF_DROP;
-	ret = tcpmss_mangle_packet(skb, par->targinfo,
+	ret = tcpmss_mangle_packet(skb, par,
 				   tcpmss_reverse_mtu(skb, PF_INET6),
 				   tcphoff,
 				   sizeof(*ipv6h) + sizeof(struct tcphdr));