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Date: Fri, 17 May 2019 16:38:51 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Kees Cook <keescook@...omium.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>, James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>, Nick Desaulniers <ndesaulniers@...gle.com>,
Kostya Serebryany <kcc@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, Sandeep Patil <sspatil@...roid.com>,
Laura Abbott <labbott@...hat.com>, Randy Dunlap <rdunlap@...radead.org>, Jann Horn <jannh@...gle.com>,
Mark Rutland <mark.rutland@....com>, Linux Memory Management List <linux-mm@...ck.org>,
linux-security-module <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v2 1/4] mm: security: introduce init_on_alloc=1 and
init_on_free=1 boot options
On Fri, May 17, 2019 at 3:26 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Tue, May 14, 2019 at 04:35:34PM +0200, Alexander Potapenko wrote:
> > [...]
> > diff --git a/mm/slab.h b/mm/slab.h
> > index 43ac818b8592..24ae887359b8 100644
> > --- a/mm/slab.h
> > +++ b/mm/slab.h
> > @@ -524,4 +524,20 @@ static inline int cache_random_seq_create(struct kmem_cache *cachep,
> > [...]
> > +static inline bool slab_want_init_on_free(struct kmem_cache *c)
> > +{
> > + if (static_branch_unlikely(&init_on_free))
> > + return !(c->ctor);
>
> BTW, why is this checking for c->ctor here? Shouldn't it not matter for
> the free case?
It does matter, see e.g. the handling of __OBJECT_POISON in slub.c
If we just return true here, the kernel crashes.
> > + else
> > + return false;
> > +}
>
> --
> Kees Cook
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
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