linux-kernel - Re: [PATCH] xt_request_find

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Message-ID: <Pine.LNX.4.61.0612191623490.10396@yvahk01.tjqt.qr>
Date:	Tue, 19 Dec 2006 16:27:36 +0100 (MET)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	Patrick McHardy <kaber@...sh.net>
cc:	Netfilter Developer Mailing List 
	<netfilter-devel@...ts.netfilter.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xt_request_find_match


>>>>Reusing code is a good idea, and I would like to do so from my 
>>>>match modules. netfilter already provides a xt_request_find_target() but 
>>>>an xt_request_find_match() does not yet exist. This patch adds it.
>>>
>>>Why does your match module needs to lookup other matches?
>> 
>> To use them?
>> 
>> I did not want to write
>> 
>> some_xt_target() {
>>     if(skb->nh.iph->protocol == IPPROTO_TCP)
>>         do_this();
>>     else
>>         do_that();
>> }
>
>I don't think
>
>xt_request_find_match(match->family, "tcp", 0)->match(lots of arguments)
>
>is better than a simple comparison. Besides that the tcp match itself
>expects that the protocol match already checked for IPPROTO_TCP, so
>you'd still have to do it.
>>     /* To quote Alan:
>> 
>>        Don't allow a fragment of TCP 8 bytes in. Nobody normal
>>        causes this. Its a cracker trying to break in by doing a
>>        flag overwrite to pass the direction checks.
>>     */
>
>This check makes sure the flags are not overwritten _after you
>matched on them_. It doesn't matter at all if you're only
>interested in the protocol since the user didn't tell you to care.

Ok, but let's say I wanted to use a bigger match module (layer7, anyone?)
Then it's just not if(protocol == IPPROTO_TCP). What's the preferred solution
then?


	-`J'
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