Re: [PATCH] mm: Add additional consistency check

[Kees Cook]

On Tue, Apr 4, 2017 at 8:58 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> On Tue 04-04-17 08:46:02, Kees Cook wrote:
>> On Tue, Apr 4, 2017 at 8:16 AM, Michal Hocko <mhocko@xxxxxxxxxx> 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