linux-kernel - Re: [PATCH] mm/slub: do not place freelist pointer to middle of object if redzone is on

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Message-ID: <202004251547.0F8E6856B@keescook>
Date:   Sat, 25 Apr 2020 15:48:31 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Changbin Du <changbin.du@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/slub: do not place freelist pointer to middle of
 object if redzone is on

On Sat, Apr 25, 2020 at 05:13:38PM +0800, Changbin Du wrote:
> The recent kernel fails to boot when slub redzone is turned on. This is
> caused by commit 3202fa62fb ("slub: relocate freelist pointer to middle of
> object") which relocates freelist pointer to middle of object. In this
> case, get_track() gets a wrong address and then the redzone is overwritten.

Hi! A fix for this is already in -next:

https://www.ozlabs.org/~akpm/mmotm/broken-out/slub-avoid-redzone-when-choosing-freepointer-location.patch

the above doesn't disable the mitigation when using redzones, so I
prefer that to this suggested solution.

-- 
Kees Cook