netdev - Re: [PATCH 1/4] netfilter: xt_connlimit: fix daddr connlimit in SNAT scenario

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Date:	Mon, 14 Mar 2011 20:00:07 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Changli Gao <xiaosuo@...il.com>
cc:	Patrick McHardy <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 1/4] netfilter: xt_connlimit: fix daddr connlimit in SNAT
 scenario

On Monday 2011-03-14 13:42, Changli Gao wrote:

>On Mon, Mar 14, 2011 at 8:26 PM, Jan Engelhardt <jengelh@...ozas.de> wrote:
>> On Monday 2011-03-14 07:50, Changli Gao wrote:
>>
>>>We use the reply tuples when limiting the connections by the destination
>>>addresses, however, in SNAT scenario, the final reply tuples won't be
>>>ready until SNAT is done in POSTROUING or INPUT chain
>>
>> If I am not mistaken: if you do daddr counting, SNAT is irrelevant.
>> Consider ruleset
>>  -t nat -A PREROUTING -p tcp --dport 80 -j DNAT --to 1.2.3.4:80
>>  -t nat -A PREROUTING -p tcp --dport 443 -j DNAT --to 1.2.3.5:443
>>
>> The tuple will first be (as per conntrack -L):
>>  src=home dst=router src=router dst=home
>> After DNAT:
>>  src=home dst=router src=1.2.3.4 dst=home
>>
>> Thus looking at the src of the reply tuple seems correct — at least this
>> is what was wanted, counting per stashed servers (=1 customer), not per
>> globally visible address.
>>
>
>Yes, you are correct only when there is no SNAT rule. If there is an 
>SNAT rule:
>
>-t nat -A POSTROUTING -p tcp --dport 80 -j SNAT --to-source 192.168.0.1
>
>the final tuples will be:
>src = home dst = router src=1.2.3.4 dst=192.168.0.1
>
>However, the tuple saved by connlimit is src=1.2.3.4 dst=home, so this
>conn will be removed later as there isn't any conntrack, which has
>this tuple in any direction.

But I don't yet see how your patch #1 can help. At the time 
conn->tuple = *tuple is done, *tuple still contains the non-SNATed 
tuple, and it is never updated again.


(Patrick: patches 2-4 are ok)

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