netdev - Re: TCP port randomization

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Message-ID: <Pine.LNX.4.64.0710180026020.12701@bizon.gios.gov.pl>
Date:	Thu, 18 Oct 2007 00:31:13 +0200 (CEST)
From:	Krzysztof Oledzki <olel@....pl>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
cc:	netdev@...r.kernel.org
Subject: Re: TCP port randomization



On Wed, 17 Oct 2007, Stephen Hemminger wrote:

> On Wed, 17 Oct 2007 23:15:48 +0200 (CEST)
> Krzysztof Oledzki <olel@....pl> wrote:
>
>> Hello,
>>
>> Is it normal that TCP port randomization (tested with 2.6.22) works only
>> when explicitly binding to a IP address:
>>
>>
>> --- cut here ---
>> root@fw1:~# nc 192.168.129.28 11
>> (UNKNOWN) [192.168.129.28] 11 (systat) : Connection refused
>> root@fw1:~# nc 192.168.129.28 11
>> (UNKNOWN) [192.168.129.28] 11 (systat) : Connection refused
>> root@fw1:~# nc 192.168.129.28 11
>> (UNKNOWN) [192.168.129.28] 11 (systat) : Connection refused
>>
>> 23:11:11.896126 IP 192.168.129.2.37839 > 192.168.129.28.11: S
>> 23:11:12.146573 IP 192.168.129.2.37840 > 192.168.129.28.11: S
>> 23:11:12.396488 IP 192.168.129.2.37841 > 192.168.129.28.11: S
>> --- cut here ---
>>
>>
>> --- cut here ---
>> root@fw1:~# nc -s 192.168.129.2 192.168.129.28 11
>> (UNKNOWN) [192.168.129.28] 11 (systat) : Connection refused
>> root@fw1:~# nc -s 192.168.129.2 192.168.129.28 11
>> (UNKNOWN) [192.168.129.28] 11 (systat) : Connection refused
>> root@fw1:~# nc -s 192.168.129.2 192.168.129.28 11
>> (UNKNOWN) [192.168.129.28] 11 (systat) : Connection refused
>>
>> 23:11:31.704391 IP 192.168.129.2.57204 > 192.168.129.28.11: S
>> 23:11:34.400048 IP 192.168.129.2.14512 > 192.168.129.28.11: S
>> 23:11:34.606707 IP 192.168.129.2.20117 > 192.168.129.28.11: S
>> --- cut here ---
>>
>> Best regards,
>>
>>  				Krzysztof Olędzki
>
> It is a expected side effect.

So it is not possible to use randomization without binding to a specific 
srcip?

> The starting point for the search
> is based on hash(srcaddr, dstaddr, dstport, secret).
> You are using same source, dest and port so yes it will stay
> the same until rekeying occurs.
> The secret only changes every 5min same as TCP initial sequence number.

If I get it right, even with explicitly selected constant srcaddr port 
numbers should simply increase? This is not what I observed.

Thanks.

Best regards,

 				Krzysztof Olędzki