linux-kernel - Re: [PATCH v2 1/2] kasan: catch invalid free before SLUB reinitializes the object

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Message-ID: <CAG48ez1d-iiWmt55-1+H4z=Didw=NaKZ0-f+RP7tSRwRNsiSyQ@mail.gmail.com>
Date: Thu, 25 Jul 2024 12:54:09 +0200
From: Jann Horn <jannh@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>, Alexander Potapenko <glider@...gle.com>, 
	Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>, 
	Vincenzo Frascino <vincenzo.frascino@....com>, Christoph Lameter <cl@...ux.com>, 
	Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, 
	Joonsoo Kim <iamjoonsoo.kim@....com>, Vlastimil Babka <vbabka@...e.cz>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Hyeonggon Yoo <42.hyeyoo@...il.com>, 
	Marco Elver <elver@...gle.com>, kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCH v2 1/2] kasan: catch invalid free before SLUB
 reinitializes the object

On Wed, Jul 24, 2024 at 11:17 PM Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Wed, 24 Jul 2024 18:34:12 +0200 Jann Horn <jannh@...gle.com> wrote:
>
> > Currently, when KASAN is combined with init-on-free behavior, the
> > initialization happens before KASAN's "invalid free" checks.
> >
> > More importantly, a subsequent commit will want to use the object metadata
> > region to store an rcu_head, and we should let KASAN check that the object
> > pointer is valid before that. (Otherwise that change will make the existing
> > testcase kmem_cache_invalid_free fail.)
> >
> > So add a new KASAN hook that allows KASAN to pre-validate a
> > kmem_cache_free() operation before SLUB actually starts modifying the
> > object or its metadata.
>
> I added this, to fix the CONFIG_KASAN=n build

Whoops, thanks for fixing that up.