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
next prev 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 [PATCH] slub: Relocate freelist pointer to middle of object 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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