TCP ack in libnetfilter_queue

TCP ack in libnetfilter_queue

[Mistick Levi]

Hey,

i wrote a filter using libnetfilter_queue api, and i want to send
messages to the queue in a specific way...
I want to get the first packet after the TCP 3-way-handshak is
finished ( meaning - only data!)..

i tried using conntrack with "ESTABLISHED" status, but then i start
getting messages to the queue from the last message of the
handshake... ( meaning the last ack )... and i dont want that since it
contain no data....

any help will be appreciated.. thanks.

Yechiel Levi

Fwd: TCP ack in libnetfilter_queue

[Mistick Levi]

Hi,
did'nt get any reply on the users list.... Hope anyone here could help out.


---------- Forwarded message ----------
From: Mistick Levi <gmistick@gmail.com>
Date: Thu, Sep 23, 2010 at 4:12 PM
Subject: TCP ack in libnetfilter_queue
To: netfilter@vger.kernel.org


Hey,

i wrote a filter using libnetfilter_queue api, and i want to send
messages to the queue in a specific way...
I want to get the first packet after the TCP 3-way-handshak is
finished ( meaning - only data!)..

i tried using conntrack with "ESTABLISHED" status, but then i start
getting messages to the queue from the last message of the
handshake... ( meaning the last ack )... and i dont want that since it
contain no data....

any help will be appreciated.. thanks.

Yechiel Levi

Re: Fwd: TCP ack in libnetfilter_queue

[Eric Leblond]

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Hi,

Le dimanche 26 septembre 2010 à 07:53 +0200, Mistick Levi a écrit :
> Hi,
> did'nt get any reply on the users list.... Hope anyone here could help out.
> 
> 
> ---------- Forwarded message ----------
> From: Mistick Levi <gmistick@gmail.com>
> Date: Thu, Sep 23, 2010 at 4:12 PM
> Subject: TCP ack in libnetfilter_queue
> To: netfilter@vger.kernel.org
> 
> 
> Hey,
> 
> i wrote a filter using libnetfilter_queue api, and i want to send
> messages to the queue in a specific way...
> I want to get the first packet after the TCP 3-way-handshak is
> finished ( meaning - only data!)..
> 
> i tried using conntrack with "ESTABLISHED" status, but then i start
> getting messages to the queue from the last message of the
> handshake... ( meaning the last ack )... and i dont want that since it
> contain no data....

What about filtering on PSH, something like:
	iptables XXXXX --tcp-flags PSH, PSH -j NFQUEUE
Not really strict but it should work in most case.
Or you can work on packet length, if it has data it is bigger:
 	iptables XXXXX --length 60:1500 -j NFQUEUE

BR,
-- 
Éric Leblond <eric@inl.fr>
EdenWall, http://www.edenwall.com/
NuFW, http://www.nufw.org

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Fwd: Fwd: TCP ack in libnetfilter_queue

[Mistick Levi]

Hi,
Thanks for the reply, i'll give it a go..

but i was wondering if maybe there should be added a new FLAG for the
connection tracking... since i belive most people think that
"ESTABLISHED" mean's after the 3way handshake and the start of the
session....
any Idea's on why is the "ESTABLISHED" state is on before the 3-way
handshake is finished... or maybe there is another flag that would
help?

Thanks in advance..
Yechiel Levi

2010/9/27 Eric Leblond <eric@inl.fr>:
> Hi,
>
> Le dimanche 26 septembre 2010 à 07:53 +0200, Mistick Levi a écrit :
>> Hi,
>> did'nt get any reply on the users list.... Hope anyone here could help out.
>>
>>
>> ---------- Forwarded message ----------
>> From: Mistick Levi <gmistick@gmail.com>
>> Date: Thu, Sep 23, 2010 at 4:12 PM
>> Subject: TCP ack in libnetfilter_queue
>> To: netfilter@vger.kernel.org
>>
>>
>> Hey,
>>
>> i wrote a filter using libnetfilter_queue api, and i want to send
>> messages to the queue in a specific way...
>> I want to get the first packet after the TCP 3-way-handshak is
>> finished ( meaning - only data!)..
>>
>> i tried using conntrack with "ESTABLISHED" status, but then i start
>> getting messages to the queue from the last message of the
>> handshake... ( meaning the last ack )... and i dont want that since it
>> contain no data....
>
> What about filtering on PSH, something like:
>        iptables XXXXX --tcp-flags PSH, PSH -j NFQUEUE
> Not really strict but it should work in most case.
> Or you can work on packet length, if it has data it is bigger:
>        iptables XXXXX --length 60:1500 -j NFQUEUE
>
> BR,
> --
> Éric Leblond <eric@inl.fr>
> EdenWall, http://www.edenwall.com/
> NuFW, http://www.nufw.org
>
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