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Possible ip_defrag DoS ?

To: Patrick McHardy <kaber@xxxxxxxxx>
Subject: Possible ip_defrag DoS ?
From: Harald Welte <laforge@xxxxxxxxxxxxx>
Date: Sun, 16 Feb 2003 21:11:54 +0100
Cc: Don Cohen <don-netf@xxxxxxxxxxxxxxxx>, netfilter-devel@xxxxxxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx
In-reply-to: <3E4F8660.5020409@trash.net>
Mail-followup-to: Harald Welte <laforge@xxxxxxxxxxxxx>, Patrick McHardy <kaber@xxxxxxxxx>, Don Cohen <don-netf@xxxxxxxxxxxxxxxx>, netfilter-devel@xxxxxxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx
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On Sun, Feb 16, 2003 at 01:38:56PM +0100, Patrick McHardy wrote:

> inerestingly, it seems linux defragmentation is vulnerable to dos attack.
> the evictor (called before defragmentation) just kills the oldest entry
> of each hash slot, starting with 0 until memory is below
> sysctl_ipfrag_low_thresh. by sending enough fragments 
> (>sysctl_ipfrag_high_thresh) which hash to the highest bucket you can
> stop reassembly of valid packets.

I'm forwarding this (from netfilter-devel) to the linux networking
developers at netdev@xxxxxxxxxxxx  If your assumption is valid, they
might want to have a look at this...

thanks.

> Patrick

-- 
- Harald Welte <laforge@xxxxxxxxxxxxx>             http://www.netfilter.org/
============================================================================
  "Fragmentation is like classful addressing -- an interesting early
   architectural error that shows how much experimentation was going
   on while IP was being designed."                    -- Paul Vixie

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