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Date: Sun, 15 Mar 2009 14:11:50 +0300
From: Sergey Matveychuk <sem@FreeBSD.org>
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To: Luigi Rizzo <rizzo@iet.unipi.it>
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Cc: freebsd-ipfw@freebsd.org, Dmitriy Demidov <dima_bsd@inbox.lv>
Subject: Re: keep-state rules inadequately handles big UDP
 packets	or	fragmented IP packets?
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Sergey Matveychuk wrote:
> Luigi Rizzo wrote:
>> On Sun, Mar 15, 2009 at 12:38:37PM +0300, Sergey Matveychuk wrote:
>>> Dmitriy Demidov wrote:
>>>> Hi Luigi. Thank you for answer.
>>>> It is a big "surprise" for me that reassembling of IP datagrams is 
>>>> done not *before* they go into firewall, but *after* :(
>>> But what's wrong with it? A fragment got from net, pass firewall and 
>>> store. After all fragments we got, OS reassembly a packet and pass it 
>>> through firewall again.
>>
>> Currently we don't have a way to re-invoke the firewall after
>> reassembly. In fact, we should probably provide hooks before and
>> after reassembly, and use them in a configurable way.
> 
> It sounds like a security issue. We can construct any packet that pass 
> through firewall?
> 

Well, I see a first fragment will be checked. But anyway I think the 
reassembled package must pass firewall again.

-- 
Dixi.
Sem.