netdev - Re: [RFC PATCH net-next 0/7 v2]IPv6:netfilter: defragment

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Date:	Thu, 25 Mar 2010 17:13:56 +0800
From:	Shan Wei <shanwei@...fujitsu.com>
To:	Pascal Hambourg <pascal.mail@...uf.fr.eu.org>
CC:	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	David Miller <davem@...emloft.net>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Yasuyuki KOZAKAI <yasuyuki.kozakai@...hiba.co.jp>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	netfilter-devel@...r.kernel.org
Subject: Re: [RFC PATCH net-next 0/7 v2]IPv6:netfilter: defragment

Pascal Hambourg wrote, at 03/25/2010 04:38 PM:
> Hello,
> 
> Jozsef Kadlecsik a écrit :
>> On Wed, 24 Mar 2010, YOSHIFUJI Hideaki wrote:
>>
>>>> In this case without conntrack, IPv6 would send an ICMPv6 message,
>>>> so in my opinion the transparent thing to do would be to still send
>>>> them. Of course only if reassembly is done on an end host.
>>> Well, no.  conntrack should just forward even uncompleted fragments
>>> to next process (e.g. core ipv6 code), and then the core would send
>>> ICMP error back.  ICMP should be sent by the core ipv6 code according
>>> to decision of itself, not according to netfilter.
>> But what state could be associated by conntrack to the uncompleted 
>> fragments but the INVALID state? In consequence, in any sane setup, the 
>> uncompleted fragments will be dropped silently by a filter table rule
>> and no ICMP error message will be sent back.
> 
> AFAIK, in the IPv4 stack the reassembly takes place before the INPUT
> chains (NF_IP_LOCAL_IN hook). Is it different in the IPv6 stack ?

Yes, they are different.

In IPv4 stack，for an end host, ip_local_deliver() reassemble 
fragments before LOCAL_IN hook .

But in IPv6 stack, ip6_input_finish() handles fragment extension headers
and try to reassemble them *after* LOCAL_IN hook.

-- 
Best Regards
-----
Shan Wei
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