netdev - Re: Question: should local address be expired when updating PMTU?

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Message-ID: <20150203120140.GU13046@secunet.com>
Date:	Tue, 3 Feb 2015 13:01:41 +0100
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	shengyong <shengyong1@...wei.com>
CC:	<davem@...emloft.net>, <netdev@...r.kernel.org>,
	<yangyingliang@...wei.com>, <hannes@...hat.com>
Subject: Re: Question: should local address be expired when updating PMTU?

On Tue, Feb 03, 2015 at 06:54:19PM +0800, shengyong wrote:
> 
> 
> 在 2015/2/3 17:28, Steffen Klassert 写道:
> > On Mon, Feb 02, 2015 at 04:20:24PM +0800, shengyong wrote:
> > 
> > We first need to find out why you receive this Packet Too Big message,
> The packet is sent by a commercial-off-the-shelf testcase, and I can reproduce the
> situation by using scapy and creating a packet as the following:
> 
> 	$ cat packet-too-big.py
> 	#!/usr/bin/python
> 	
> 	from scapy.all import *
> 
> 	# fe80::800:27ff:fe00:0 is linklocal addr of PC
> 	# fe80::a00:27ff:fe1a:e2a0 is linklocal addr of VM
> 	base=IPv6(src='fe80::800:27ff:fe00:0',dst='fe80::a00:27ff:fe1a:e2a0')
> 	pkt_too_big=ICMPv6PacketTooBig(mtu=1024)
> 	ext_base=IPv6(src='fe80::a00:27ff:fe1a:e2a0',dst='fe80::a00:27ff:fe1a:e2a0',plen=24)
> 	ext_nd_na=ICMPv6ND_NA()
> 	
> 	packet=base/pkt_too_big/ext_base/ext_nd_na
> 	send(packet)

So it is not a valid pmtu update, this make life easier.

Can you please test the patch below (compile tested only)?

This should fix your problem, and in combination with the two patches I sent
out last week, it should cure the whole 'expiring of uncached routes' problem.

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 49596535..4ccfb9c 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1156,7 +1156,8 @@ static void ip6_rt_update_pmtu(struct dst_entry *dst, struct sock *sk,
 	struct rt6_info *rt6 = (struct rt6_info *)dst;
 
 	dst_confirm(dst);
-	if (mtu < dst_mtu(dst) && rt6->rt6i_dst.plen == 128) {
+	if (mtu < dst_mtu(dst) && rt6->rt6i_dst.plen == 128 &&
+	    (rt6->rt6i_flags & RTF_CACHE)) {
 		struct net *net = dev_net(dst->dev);
 
 		rt6->rt6i_flags |= RTF_MODIFIED;
--
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