[3.11.y.z extended stable] Patch "net: ipv6: send pkttoobig immediately if orig frag size > mtu" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    net: ipv6: send pkttoobig immediately if orig frag size > mtu

to the linux-3.11.y-queue branch of the 3.11.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-3.11.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 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 3e694f6ea8ce92e4ed5bb820fbf1b7ef742053e5 Mon Sep 17 00:00:00 2001
From: Florian Westphal <fw at strlen.de>
Date: Mon, 5 May 2014 00:03:34 +0200
Subject: net: ipv6: send pkttoobig immediately if orig frag size > mtu

commit 418a31561d594a2b636c1e2fa94ecd9e1245abb1 upstream.

If conntrack defragments incoming ipv6 frags it stores largest original
frag size in ip6cb and sets ->local_df.

We must thus first test the largest original frag size vs. mtu, and not
vice versa.

Without this patch PKTTOOBIG is still generated in ip6_fragment() later
in the stack, but

1) IPSTATS_MIB_INTOOBIGERRORS won't increment
2) packet did (needlessly) traverse netfilter postrouting hook.

Fixes: fe6cc55f3a9 ("net: ip, ipv6: handle gso skbs in forwarding path")
Signed-off-by: Florian Westphal <fw at strlen.de>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/ipv6/ip6_output.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index d18c00a36fde..fe0bc8e0e866 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -348,12 +348,16 @@ static inline int ip6_forward_finish(struct sk_buff *skb)

 static bool ip6_pkt_too_big(const struct sk_buff *skb, unsigned int mtu)
 {
-	if (skb->len <= mtu || skb->local_df)
+	if (skb->len <= mtu)
 		return false;

+	/* ipv6 conntrack defrag sets max_frag_size + local_df */
 	if (IP6CB(skb)->frag_max_size && IP6CB(skb)->frag_max_size > mtu)
 		return true;

+	if (skb->local_df)
+		return false;
+
 	if (skb_is_gso(skb) && skb_gso_network_seglen(skb) <= mtu)
 		return false;

--
1.9.1