Date: Fri, 14 Nov 1997 23:23:37 -0500 From: Mike Tancsa <mike@sentex.net> To: questions@freebsd.org Cc: security@freebsd.org Subject: IPFW and ipfragment overlap attack... Message-ID: <3.0.2.32.19971114232337.02496330@sentex.net>
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Does anyone know of a way to prevent via ipfw the use of the ip fragment
attack that was posted on bugtraq the other day ? Since this can take out
NT/95 machines at will, it would be nice if I could protect my dialup users
from outside attack. Also, it seems that FreeBSD is safe against this
program is it not ? I am not a network programmer, but looking through
/usr/src/sys/netinet/ip_input.c there are some safegaurds against this.
Are there any modifications to the program that could effect FreeBSD ?
---Mike
>Approved-By: aleph1@UNDERGROUND.ORG
>X-Mailer: ELM [version 2.4 PL25]
>Date: Thu, 13 Nov 1997 22:06:15 -0800
>Reply-To: route@RESENTMENT.INFONEXUS.COM
>Sender: Bugtraq List <BUGTRAQ@NETSPACE.ORG>
>From: G P R <route@RESENTMENT.INFONEXUS.COM>
>Subject: Linux IP fragment overlap bug
>To: BUGTRAQ@NETSPACE.ORG
>
>
> As it happens, Linux has a serious bug in it's IP fragmentation module.
>More specifically, in the fragmentation reassembly code. More specifically,
>the bug manifests itself in the `ip_glue()` function....
>
> When Linux reassembles IP fragments to form the original IP datagram, it
>runs in a loop, copying the payload from all the queued fragments into a
newly
>allocated buffer (which would then normally be passed to the IP layer
proper).
>From ip_fragment.c@376:
>
> fp = qp->fragments;
> while(fp != NULL)
> {
> if(count+fp->len > skb->len)
> {
> error_to_big;
> }
> memcpy((ptr + fp->offset), fp->ptr, fp->len);
> count += fp->len;
> fp = fp->next;
> }
>
> While it does check to see if the fragment length is too large, which
would
>have the kernel copy too much data, it doesn't check to see if the fragment
>length is too small, which would have the kernel copy WAY too data (such
is the
>case if fp->len is < 0).
**********************************************************************
Mike Tancsa (mike@sentex.net) * To do is to be -- Nietzsche
Sentex Communications Corp, * To be is to do -- Sartre
Cambridge, Ontario * Do be do be do -- Sinatra
(http://www.sentex.net/~mdtancsa) *
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