netdev - Re: [PATCH] bridge: netfilter: work around shared nfct struct

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Date:	Tue, 30 Aug 2011 15:08:13 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Florian Westphal <fw@...len.de>
CC:	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] bridge: netfilter: work around shared nfct struct

On 30.08.2011 14:54, Florian Westphal wrote:
> Patrick McHardy <kaber@...sh.net> wrote:
>> On 30.08.2011 12:57, Florian Westphal wrote:
>>> When incoking iptables hooks from bridge netfilter, the assumption
>>> that non-confirmed skb->nfct is never shared does no longer hold,
>>> as bridge code clones skbs when e.g. forwarding packets to multiple
>>> bridge ports.
>>>
>>> When NFQUEUE is used, we can BUG because nf_nat_setup_info can be
>>> invoked simultaneously for the same conntrack:
>>
>> I'm wondering how this can happen, when flooding packets to multiple
>> ports, they are still processed by the same CPU one after another,
>> so for the second and further packets, nf_nat should notice that
>> the mappings are already set up.
> 
> Main problem is that we end up with same ->nfct in both
> INPUT and POSTROUTING (br_pass_frame_up vs. br_forward).
> 
> its extremely unlikely but reproduceable with something like
> hping2 -i u1200 -2 -p 138 -d 128 192.168.0.255
> 
> (assuming bridge interface has an address within that network).
> 
> Also, with recent change nf_reinject can be run in parallel.
> (the original problem was observed on 2.6.32.24, but i can
>  reproduce it with nf-next, too).

I see. We still need to avoid the module dependency on nf_conntrack
though, so I think this will have to be fixed in nf_nat_fn().
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