Re: [PATCH 22/23] usercopy: split user-controlled slabs to separate caches

[Michal Hocko]

On Tue 27-06-17 15:07:17, Kees Cook wrote:
> On Tue, Jun 27, 2017 at 12:31 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> > But I am not really sure I understand consequences of this patch. So how
> > do those attacks look like. Do you have an example of a CVE which would
> > be prevented by this measure?
> 
> It's a regular practice, especially for heap grooming. You can see an
> example here:
> http://cyseclabs.com/blog/cve-2016-6187-heap-off-by-one-exploit
> which even recognizes this as a common method, saying "the standard
> msgget() technique". Having the separate caches doesn't strictly
> _stop_ some attacks, but it changes the nature of what the attacker
> has to do. Instead of having a universal way to groom the heap, they
> must be forced into other paths. Generally speaking this can reduce
> what's possible making the attack either impossible, more expensive to
> develop, or less reliable.

Thanks that makes it more clear to me. I believe this would be a useful
information in the changelog.

> >> This would mean building out *_user() versions for all the various
> >> *alloc() functions, though. That gets kind of long/ugly.
> >
> > Only prepare those which are really needed. It seems only handful of
> > them in your patch.
> 
> Okay, if that's the desired approach, we can do that.

yes please
-- 
Michal Hocko
SUSE Labs