linux-kernel - Re: [PATCH] slub: Relocate freelist pointer to middle of object

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Message-ID: <alpine.DEB.2.21.2003081919290.14266@www.lameter.com>
Date:   Sun, 8 Mar 2020 19:21:09 +0000 (UTC)
From:   Christopher Lameter <cl@...ux.com>
To:     Kees Cook <keescook@...omium.org>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Daniel Micay <danielmicay@...il.com>,
        Vitaly Nikolenko <vnik@...synt.com>,
        Silvio Cesare <silvio.cesare@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] slub: Relocate freelist pointer to middle of object

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.

Acked-by: Christoph Lameter <cl@...ux.com>