netdev - Re: Passive OS fingerprinting.

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Date:	Tue, 1 Jul 2008 16:03:20 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org
Subject: Re: Passive OS fingerprinting.

Hi Patrick.

On Tue, Jul 01, 2008 at 01:53:43PM +0200, Patrick McHardy (kaber@...sh.net) wrote:
> My two main objections are that this only works for TCP and
> can be trivially evaded. What use cases does it have?

Yes, it is TCP specific module.

> I'm also wondering whether this couldn't be implemented
> using the u32 match.

I'm not sure it is that simple. OSF uses common rules database
shared with OpenBSD (and other *BSDs as well), so converting it into u32
match would require noticeble efforts. But in theory it is probably
doable.

> >This version existed quite for a while in patch-o-matic(-ng), but
> >suddenly was dropped and then only was updated on its own repo:
> >http://tservice.net.ru/~s0mbre/old/?section=projects&item=osf
> >
> >I've updated OSF to match new iptables standards (namely xtables
> >support) and present new kernelspace and userspace library files in
> >attach.
> >
> >To setup single rule, which will drop and log all Linux incoming
> >access one needs to do following steps:
> ># insmod ./ipt_osf.ko
> ># ./load ./pf.os /proc/sys/net/ipv4/osf
> ># iptables -I INPUT -j DROP -p tcp -m osf --genre Linux --log 2 \
> >--ttl 2 --connector
> 
> And I don't think it should be using connector. AFAIK we
> only have a single user in the tree currently and new
> stuff usually uses genetlink (which is pretty similar),
> so we might be able to remove connection in the future
> unless we add new users. But netfilter modules should
> use nfnetlink anyway.
 
This module was created way before genetlink was ever designed (on
behalf of connector btw :)

Also I do not know why we want to remove connector in favour of
genetlink, since the former is much simpler to work with. Connector
logging is optional in OSF.

-- 
	Evgeniy Polyakov
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