linux-kernel - Re: [PATCH 1/2] LSM: Do not apply mmap_min_addr check to PROT

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Date:	Mon, 24 Oct 2011 11:07:48 -0400
From:	Eric Paris <eparis@...isplace.org>
To:	Roland McGrath <roland@...k.frob.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Morris <jmorris@...ei.org>,
	Stephen Smalley <sds@...ho.nsa.gov>, selinux@...ho.nsa.gov,
	John Johansen <john.johansen@...onical.com>,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] LSM: Do not apply mmap_min_addr check to PROT_NONE
 mappings

On Sun, 2011-10-23 at 11:52 -0700, Roland McGrath wrote:

> > But that's no reason for the kernel to *allow* the mapping.
> 
> I don't have a problem with that.

I feel like, and it's just a very vague feeling, that the PROT bits
didn't matter to the kernel.  It would still happily execute stuff on
page 0 even without PROT_EXEC at some point in the past.  I'm probably
totally off base, and I could test it, but I sort of feel like I
remember something like that....

If that's the case, NULL pointer kernel bugs won't be caught if they
happen while these are mapped by your program...

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