From: Olivier Galibert <galibert@pobox.com>
To: linux-kernel@vger.kernel.org
Subject: Re: Cursed Checksums
Date: Mon, 23 Aug 2004 00:58:33 +0200 [thread overview]
Message-ID: <20040822225833.GA5225@dspnet.fr.eu.org> (raw)
In-Reply-To: <S268085AbUHVUD4/20040822200356Z+207@vger.kernel.org>
On Sun, Aug 22, 2004 at 11:03:54PM +0200, Josan Kadett wrote:
> Perhaps there is a way to recompute IP header checksums before they get into
> the interface? As I outlined, I have found a way to manipulate IP source
> address before the packet is flushed to system, but a means of recalculating
> the IP header checksum after that manipulation should be found. Because even
> if I ignore IP header CRC in one system, all other boxes connected to this
> machine has to be patched the same. That is impossible anyway.
>
> Only if I could find a way to recalculate the checksum in IP headers by
> doing a simple hack to the kernel, everything would be alright.
Why don't you patch the checksum when you change the IP? It's just a
not of the sum the 16-bit words so take the old one, not it, add the
two 16-bits differences, re-not it and write it back.
OG.
next prev parent reply other threads:[~2004-08-22 22:58 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-08-21 2:37 Cursed Checksums Josan Kadett
2004-08-22 11:40 ` Alan Cox
2004-08-22 19:39 ` Josan Kadett
2004-08-22 21:03 ` Josan Kadett
2004-08-22 20:36 ` Alan Cox
2004-08-22 22:58 ` Olivier Galibert [this message]
2004-08-23 0:05 ` Josan Kadett
-- strict thread matches above, loose matches on Subject: below --
2004-08-22 18:55 Albert Cahalan
2004-08-22 22:38 ` Josan Kadett
[not found] <E1Bz02y-00052n-3Z@sc8-sf-mx2.sourceforge.net>
2004-08-22 20:14 ` Albert Cahalan
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