netdev - Re: [PATCH] netfilter: Fix br_nf_pre_routing() in conjunction with bridge-nf-call-ip(6)tables=0

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Date:	Tue, 03 Jan 2012 21:15:19 +0100
From:	Bart De Schuymer <bdschuym@...dora.be>
To:	Richard Weinberger <richard@....at>
CC:	Stephen Hemminger <shemminger@...tta.com>, davem@...emloft.net,
	bridge@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org
Subject: Re: [PATCH] netfilter: Fix br_nf_pre_routing() in conjunction with
 bridge-nf-call-ip(6)tables=0

Op 3/01/2012 18:42, Richard Weinberger schreef:
> Am 03.01.2012 17:15, schrieb Stephen Hemminger:
>> On Tue,  3 Jan 2012 14:26:04 +0100
>> Richard Weinberger<richard@....at>  wrote:
>>
>>> If net.bridge.bridge-nf-call-iptables or net.bridge.bridge-nf-call-ip6tables
>>> are set to zero xt_physdev has no effect because skb->nf_bridge has not been set up.
>>>
>>> Signed-off-by: Richard Weinberger<richard@....at>
>> I am not sure if this is a valid configuration. The setting of sysctl is saying
>> "don't do iptables on bridge (since I won't be using it)" and then you are later
>> doing iptables and expecting the settings as if the iptables setup was being
>> done.
> I don't think so.
>
> Also rules like this one are broken:
> iptables -A INPUT -i bridge0 -m physdev --physdev-in eth0 -j ...
>
> No firewalling is done on the bridge, xt_physdev is only using some meta
> information.
>
> At least a big fat warning would be nice that xt_physdev does not work
> if bridge-nf-call-iptables=0.
> It took me some time to figure out why my firewall rule set gone nuts on
> RHEL6...

The documentation is probably not explicit enough, but I would keep the 
behavior as it is now. Setting bridge-nf-call-iptables to 0 makes 
iptables behave as if bridge-netfilter was not enabled at compilation.
Anyway, your patch is almost certainly flawed since the fact that 
skb->nf_bridge can be NULL is used as part of the logic in 
br_netfilter.c: it indicates that bridge-nf-call-iptables was 0 when the 
packet was first processed by bridge-netfilter and should therefore not 
be given to iptables in any other netfilter hook.

cheers,
Bart


-- 
Bart De Schuymer
www.artinalgorithms.be

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