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

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Date:	Wed, 3 Jun 2009 11:50:16 -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, Linus Torvalds wrote:
> 
> 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.

Btw, you obviously need to then _also_ pair it with some as-yet-unknown 
case of kernel bug to get to that NULL pointer (or zero-sized-alloc 
pointer) problem. 

You _also_ seem to be totally ignoring the fact that we already _do_ 
protect against NULL pointers by default.

So I really don't see why you're making a big deal of this. It's as if you 
were talking about us not randomizing the address space - sure, you can 
turn it off, but so what? We do it by default.

So it boils down to:

 - NULL pointers already cannot be in mmap memory (unless a distro has 
   done something wrong - outside of the kernel)

 - What's your beef? Let it go, man.

			Linus
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