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From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
To: Pieter de Boer <pieter@thedarkside.nl>
References: <4AAF4A64.3080906@thedarkside.nl>
Date: Tue, 15 Sep 2009 14:06:34 +0200
In-Reply-To: <4AAF4A64.3080906@thedarkside.nl> (Pieter de Boer's message of
	"Tue, 15 Sep 2009 10:03:48 +0200")
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Cc: freebsd-security@freebsd.org
Subject: Re: Protecting against kernel NULL-pointer derefs
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Pieter de Boer <pieter@thedarkside.nl> writes:
> Given the amount of NULL-pointer dereference vulnerabilities in the
> FreeBSD kernel that have been discovered of late,

Specify "amount" and define "of late".

> By disallowing userland to map pages at address 0x0 (and a bit beyond),
> it is possible to make such NULL-pointer deref bugs mere DoS'es instead
> of code execution bugs. Linux has implemented such a protection for a
> long while now, by disallowing page mappings on 0x0 - 0xffff.

Yes, that really worked out great for them:

http://isc.sans.org/diary.html?storyid=3D6820

DES
--=20
Dag-Erling Sm=C3=B8rgrav - des@des.no