netdev - Re: [PATCH] bridge: make bridge-nf-call-*tables default configurable

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Message-ID: <alpine.LSU.2.00.0907010535170.6438@fbirervta.pbzchgretzou.qr>
Date:	Wed, 1 Jul 2009 05:50:18 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Herbert Xu <herbert@...dor.apana.org.au>
cc:	David Miller <davem@...emloft.net>, markmc@...hat.com,
	netdev@...r.kernel.org, kaber@...sh.net,
	netfilter-devel@...r.kernel.org
Subject: Re: [PATCH] bridge: make bridge-nf-call-*tables default
 configurable


On Wednesday 2009-07-01 03:15, Herbert Xu wrote:
>On Tue, Jun 30, 2009 at 10:16:35PM +0200, Jan Engelhardt wrote:
>>
>> It makes sense absolutely. Consider:
>> 
>> * packet enters bridge
>> * NF_HOOK(PF_INET6, NF_INET_PRE_ROUTING, ...) is called by nr_netfilter.c
>> * (connection tracking entry is set up)
>> * let bridging decision be "local delivery"
>
>No, my question is does it ever make sense to use conntrack as
>part of bridge netfilter.  That is, do you ever want to test it
>in your rules that are run as part of bridge netfilter.

There is the possibility that some users have -m conntrack in their
mangle table in the PREROUTING chain. However, I am pretty sure that
if there are such users, they do it because of the layer-3/4/5/7 part
and not care about bridge so much.

>conntrack is inherently a security hole when used as part of
>bridging, because it ignores the Ethernet header so two unrelated
>connections can be tracked as one.

On secondary thought, one could also argue that because conntrack 
ignores the interface, two unrelated connections happening to be routed 
through the same machine(*) are tracked as one, too.




(*)
ip rule iif eth0 table 7
ip rule iif eth1 table 7
ip rule iif eth2 table 8
ip rule iif eth3 table 8
ip route add 2003::1/128 dev eth0 table 7
ip route add 2003::2/128 dev eth1 table 7
ip route add 2003::1/128 dev eth2 table 8
ip route add 2003::2/128 dev eth3 table 8
(four single nets, four single hosts)
In Unicode:

    A
    0
  ┌─║───┐
B1══╝   │
  │   ╔══2C
  └───║─┘
      3
      D
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