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

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Date:	Wed, 03 Jun 2009 12:36:25 -0400
From:	Rik van Riel <riel@...hat.com>
To:	"Larry H." <research@...reption.com>
CC:	Christoph Lameter <cl@...ux-foundation.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-mm@...ck.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	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)

Larry H. wrote:

> Christopher, crippling the system is truly not the way to fix this.
> There are many legitimate users of private|fixed mappings at 0. In
> addition, if you want to go ahead and break POSIX, at least make sure
> your patch closes the loophole.

I suspect there aren't many at all, and restricting them through
SELinux may be enough to mitigate the risk.

> If SELinux isn't present, that's not useful. If mmap_min_addr is
> enabled, that still won't solve what my original, utterly simple patch
> fixes.

Would anybody paranoid run their system without SELinux?

> The patch provides a no-impact, clean solution to prevent kmalloc(0)
> situations from becoming a security hazard. Nothing else.

True, the changes in your patch only affect a few code paths.

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