netdev - Re: Passive OS fingerprint xtables match.

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Message-ID: <alpine.LSU.2.00.0902131448040.9310@fbirervta.pbzchgretzou.qr>
Date:	Fri, 13 Feb 2009 14:51:48 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Evgeniy Polyakov <zbr@...emap.net>
cc:	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Netfilter Development Mailinglist 
	<netfilter-devel@...r.kernel.org>
Subject: Re: Passive OS fingerprint xtables match.


On Friday 2009-02-13 14:03, Evgeniy Polyakov wrote:
>> >What's this? It does not exist in the net/ipv4/netfilter/Kconfig
>> 
>> net/netfilter/Kconfig: (e.g.)
>> 
>> config NETFILTER_XT_MATCH_COMMENT
>>         tristate  '"comment" match support'
>>         depends on NETFILTER_ADVANCED
>>         ---help---
>
>But I placed OSF into net/ipv4/netfilter/ipt_osf.c, should it be moved
>into different location?

That would be preferable -> net/netfilter/xt_osf.c.

>> >> >+					case OSFOPT_MSS:
>> >> >+						mss = ntohs(*(u16 *)(optp + 2));
>> >> 
>> >> This needs get_unaligned(), in case someone sends a malicious packet.
>> >
>> >Hmmm, why is this needed? We dereference linear kernel pointer at
>> >proper offset (modulo of the option size).
>> 
>> What if optp is odd?
>
>It cant, header is fixed and every option length is also fixed (and its
>size is checked).

This RFC-compliant ("An option may begin on any octet boundary.")
option byte stream seems to produce an odd optp value:

01 02 04 05 a0 00

or where did I go wrong?
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