netdev - Re: [PATCH 5/5] netfilter: xt_TEE: have cloned packet travel through Xtables too

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Message-ID: <4BB47EEA.4020809@trash.net>
Date:	Thu, 01 Apr 2010 13:09:30 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Jan Engelhardt <jengelh@...ozas.de>
CC:	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 5/5] netfilter: xt_TEE: have cloned packet travel through
 Xtables too

Jan Engelhardt wrote:
> On Thursday 2010-04-01 12:37, Patrick McHardy wrote:
> 
>> Jan Engelhardt wrote:
>>> Since Xtables is now reentrant/nestable, the cloned packet can also go
>>> through Xtables and be subject to rules itself.
>> That sounds dangerous if conntrack isn't used to prevent loops.
> 
> Conntrack loops are prevented by using a dummy conntrack, just as 
> NOTRACK does.

My question was about the case without conntrack.

>> Is that really useful? For filtering, you can simply apply the
>> rules before deciding to TEE the packet.
> 
> I can think of a handful of applications:
>  - CLASSIFY

Good point, you should probably reset a couple of skb members
after the skb_copy().

>  - When the cloned packets gets XFRMed or tunneled, its status switches 
>    from "special" to "plain". Doing policy routing on them does not seem 
>    so far-fetched.

Fair enough, provided we can also handle loops when conntrack
isn't used.
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