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

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Message-ID: <4BB4A41C.7030107@trash.net>
Date:	Thu, 01 Apr 2010 15:48:12 +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 15:22, Patrick McHardy wrote:
>>>>> Conntrack loops are prevented by using a dummy conntrack, just as 
>>>>> NOTRACK does.
>>>> [...]
>>>>>  - 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.
>>>> My question was about the case without conntrack.
>>> Hm. Do you have any suggestion in countering a case whereby a user
>>> does -I OUTPUT -j TEE without conntrack?
>>>
>>> Perhaps making nesting a feature that requires conntrack, such that the 
>>> non-CT case can't loop?
>> If we drop the reentrancy thing, what should work is to prevent
>> using loopback as output device and using something similar to
>> the recursion counters tunnel devices used to have.
> 
> Nah. I'm going to pick a bit from struct skbuff to indicate the
> packet was teed so as to avoid that loop.

That's a bad idea, we shouldn't be adding new skb members for something
as peripheral as this module.

What's wrong with adding a reentrancy counter?
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