netdev - Re: [RFC Patch net-next] ipv6: unify conntrack reassembly expire code with standard one

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Date:	Mon, 20 Aug 2012 22:21:09 +0200
From:	Michal Kubecek <mkubecek@...e.cz>
To:	Cong Wang <amwang@...hat.com>
Cc:	netdev@...r.kernel.org, Herbert Xu <herbert@...dor.hengli.com.au>,
	"David S. Miller" <davem@...emloft.net>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Shan Wei <shanwei@...fujitsu.com>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	netfilter-devel@...r.kernel.org
Subject: Re: [RFC Patch net-next] ipv6: unify conntrack reassembly expire
 code with standard one

On Mon, Aug 20, 2012 at 05:06:39PM +0800, Cong Wang wrote:
> doesn't work. I think we probably can save the struct net pointer in
> struct netns_frags during inet_frags_init_net(), so that container_of()
> can be eliminated. 

This would work but one would have to check carefully that the pointer
is always set to an usable value. Or we could just add a flag indicating
whether the structure is embedded (and if it is not, use init_net).
Another approach was suggested in the patchworks discussion: add a
special namespace for IPv6 conntrack fragment handling.

> Thanks for testing! I tried to test it too, but seems I can't trigger a
> defragment. Any hints?

I used netfilter on a computer between source and destination of the 
packets (generated with "ping6 -s 3000"):

ip6tables -A FORWARD -o ... -m frag --fragid 0:0xFFFFFFFF --fraglast -j DROP

The --fragid condition is needed to work around a bug in iptables (if 
frag module is loaded and there is no --fragid, only packets with zero
fragment id match - patch for this is already in git). On the target,
packet is defragmented automatically, by default by the "normal" code,
with nf_conntrack_ipv6 module by the conntrack code.

Setting

  echo 5 >/proc/sys/net/ipv6/ip6frag_time
  echo 5 >/proc/sys/net/netfilter/nf_conntrack_frag6_timeout

on target also helps.

                                                        Michal Kubecek

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