netdev - [PATCH BUG-FIX] ipv6: allow to send packet after receiving ICMPv6 Too Big message with MTU field less than IPV6_MIN

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Message-ID: <4BCBC6CE.9020302@cn.fujitsu.com>
Date:	Mon, 19 Apr 2010 10:58:22 +0800
From:	Shan Wei <shanwei@...fujitsu.com>
To:	David Miller <davem@...emloft.net>,
	"yoshfuji@...ux-ipv6.org >> YOSHIFUJI Hideaki" 
	<yoshfuji@...ux-ipv6.org>,
	魏勇军 <yjwei@...fujitsu.com>,
	vladislav.yasevich@...com
CC:	kuznet@....inr.ac.ru, pekkas@...core.fi, jmorris@...ei.org,
	Patrick McHardy <kaber@...sh.net>, eric.dumazet@...il.com,
	Shan Wei <shanwei@...fujitsu.com>, sri@...ibm.com,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	linux-sctp@...r.kernel.org
Subject: [PATCH BUG-FIX] ipv6: allow to send packet after receiving ICMPv6
 Too Big message with MTU field less than  IPV6_MIN_MTU


According to RFC2460, PMTU is set to the IPv6 Minimum Link
MTU (1280) and a fragment header should always be included
after a node receiving Too Big message reporting PMTU is
less than the IPv6 Minimum Link MTU.

After receiving a ICMPv6 Too Big message reporting PMTU is
less than the IPv6 Minimum Link MTU, sctp *can't* send any
data/control chunk that total length including IPv6 head 
and IPv6 extend head is less than IPV6_MIN_MTU(1280 bytes).

The failure occured in p6_fragment(), about reason 
see following(take SHUTDOWN chunk for example):
sctp_packet_transmit (SHUTDOWN chunk, len=16 byte)
|------sctp_v6_xmit (local_df=0)
   |------ip6_xmit
       |------ip6_output (dst_allfrag is ture)
           |------ip6_fragment

In ip6_fragment(), for local_df=0, drops the the packet
and returns EMSGSIZE.

The patch fixes it with adding check length of skb->len.
In this case, Ipv6 not to fragment upper protocol data,
just only add a fragment header before it. 

Signed-off-by: Shan Wei <shanwei@...fujitsu.com>
---
 net/ipv6/ip6_output.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 5129a16..c3edb6c 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -625,7 +625,7 @@ static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 	/* We must not fragment if the socket is set to force MTU discovery
 	 * or if the skb it not generated by a local socket.
 	 */
-	if (!skb->local_df) {
+	if (!skb->local_df && skb->len > mtu) {
 		skb->dev = skb_dst(skb)->dev;
 		icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
 		IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
--
1.6.3.3 
--
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