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From: Kees Cook <keescook@chromium.org>
To: 'Christopher Lameter' <cl@linux.com>
Cc: David Laight <David.Laight@ACULAB.COM>,
	Andrew Morton <akpm@linux-foundation.org>,
	Pekka Enberg <penberg@kernel.org>,
	David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Daniel Micay <danielmicay@gmail.com>,
	Vitaly Nikolenko <vnik@duasynt.com>,
	Silvio Cesare <silvio.cesare@gmail.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] slub: Relocate freelist pointer to middle of object
Date: Wed, 11 Mar 2020 10:44:09 -0700	[thread overview]
Message-ID: <202003111039.24B8A0B@keescook> (raw)
In-Reply-To: <6fbf67b5936a44feaf9ad5b58d39082b@AcuMS.aculab.com>

From: Christopher Lameter
> Sent: 08 March 2020 19:21
> 
> On Thu, 5 Mar 2020, Kees Cook wrote:
> 
> > Instead of having the freelist pointer at the very beginning of an
> > allocation (offset 0) or at the very end of an allocation (effectively
> > offset -sizeof(void *) from the next allocation), move it away from
> > the edges of the allocation and into the middle. This provides some
> > protection against small-sized neighboring overflows (or underflows),
> > for which the freelist pointer is commonly the target. (Large or well
> > controlled overwrites are much more likely to attack live object contents,
> > instead of attempting freelist corruption.)
> 
> Sounds good. You could even randomize the position to avoid attacks on via
> the freelist pointer.

That's a good point. "offset" is just calculated once, and for many
slabs, the available space is quite large. I wonder what the best
practice might be for how far from the edge to stay. Hmmm. Maybe simply
carve it into thirds, and randomize the offset within the middle third?

-- 
Kees Cook

  parent reply	other threads:[~2020-03-11 17:44 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-06  0:26 Kees Cook
2020-03-08 19:21 ` Christopher Lameter
2020-03-11 14:48   ` David Laight
2020-03-11 17:37     ` Kees Cook
2020-03-11 17:44     ` Kees Cook [this message]
2020-03-15 14:11       ` Christopher Lameter

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