linux-kernel - Re: Security fix for remapping of page 0 (was [PATCH] Change ZERO_SIZE

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Date:	Wed, 3 Jun 2009 11:45:38 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Larry H." <research@...reption.com>
cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Christoph Lameter <cl@...ux-foundation.org>,
	linux-mm@...ck.org, Rik van Riel <riel@...hat.com>,
	linux-kernel@...r.kernel.org, pageexec@...email.hu
Subject: Re: Security fix for remapping of page 0 (was [PATCH] Change
 ZERO_SIZE_PTR to point at unmapped space)



On Wed, 3 Jun 2009, Larry H. wrote:
> > 
> > The fact, the NULL pointer attack is neither easy nor common. It's 
> > perfectly reasonable to say "we'll allow mmap at virtual address zero".
> 
> And how could you calibrate if this attack venue isn't easy to take
> advantage of? Or not commonly abused? What empirical results led you to this
> conclusion?

It's not a primary attack vector. You need to have already broken local 
security to get there - you need to be able to execute code.

That means that you've already by-passed all the main security. It's thus 
by definition less common than attack vectors like buffer overflows that 
give you that capability in the first place.

			Linus
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