linux-kernel - Re: [PATCH] mm: Add additional consistency check

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Message-ID: <CAGXu5jKrs1xxfpNv9ta8XL=ii1N3uEfJMCXWkLTcoR4JMPw=kA@mail.gmail.com>
Date:   Tue, 4 Apr 2017 09:02:48 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: Add additional consistency check

On Tue, Apr 4, 2017 at 8:58 AM, Michal Hocko <mhocko@...nel.org> wrote:
> On Tue 04-04-17 08:46:02, Kees Cook wrote:
>> On Tue, Apr 4, 2017 at 8:16 AM, Michal Hocko <mhocko@...nel.org> wrote:
>> > On Tue 04-04-17 10:07:23, Cristopher Lameter wrote:
>> >> On Tue, 4 Apr 2017, Michal Hocko wrote:
>> >>
>> >> > NAK without a proper changelog. Seriously, we do not blindly apply
>> >> > changes from other projects without a deep understanding of all
>> >> > consequences.
>> >>
>> >> Functionalitywise this is trivial. A page must be a slab page in order to
>> >> be able to determine the slab cache of an object. Its definitely not ok if
>> >> the page is not a slab page.
>> >
>> > Yes, but we do not have to blow the kernel, right? Why cannot we simply
>> > leak that memory?
>>
>> I can put this behind CHECK_DATA_CORRUPTION() instead of BUG(), which
>> allows the system builder to choose between WARN and BUG. Some people
>> absolutely want the kernel to BUG on data corruption as it could be an
>> attack.
>
> CHECK_DATA_CORRUPTION sounds as better fit to me. This would, however
> require to handle the potenial corruption by returning and leaking the
> memory.

IIUC, that would be the "return s" path? I should likely change the
WARN_ON_ONCE there to be CHECK_DATA_CORRUPTION too. I'll add this to
my series.

-Kees

-- 
Kees Cook
Pixel Security