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

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Date:	Tue, 30 Aug 2011 14:54:53 +0200
From:	Florian Westphal <fw@...len.de>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Florian Westphal <fw@...len.de>, netfilter-devel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] bridge: netfilter: work around shared nfct struct

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).
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