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

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Message-ID: <20110830131905.GE7548@Chamillionaire.breakpoint.cc>
Date:	Tue, 30 Aug 2011 15:19:05 +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 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().

Right, I failed to spot the call to the destroy hook 8-/

I'll submit an alternate patch shortly.
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