Re: [PATCH -next] slub: play init_on_free=1 well with SLAB_RED_ZONE

[Alexander Potapenko]

On Fri, Jun 21, 2019 at 2:55 PM Qian Cai <cai@xxxxxx> wrote:
>
> On Thu, 2019-06-20 at 18:19 -0700, Kees Cook wrote:
> > On Thu, Jun 20, 2019 at 06:14:33PM -0700, Kees Cook wrote:
> > > On Thu, Jun 20, 2019 at 03:28:01PM -0400, Qian Cai wrote:
> > > > diff --git a/mm/slub.c b/mm/slub.c
> > > > index a384228ff6d3..787971d4fa36 100644
> > > > --- a/mm/slub.c
> > > > +++ b/mm/slub.c
> > > > @@ -1437,7 +1437,7 @@ static inline bool slab_free_freelist_hook(struct
> > > > kmem_cache *s,
> > > >           do {
> > > >                   object = next;
> > > >                   next = get_freepointer(s, object);
> > > > -                 memset(object, 0, s->size);
> > > > +                 memset(object, 0, s->object_size);
> > >
> > > I think this should be more dynamic -- we _do_ want to wipe all
> > > of object_size in the case where it's just alignment and padding
> > > adjustments. If redzones are enabled, let's remove that portion only.
> >
> > (Sorry, I meant: all of object's "size", not object_size.)
> >
>
> I suppose Alexander is going to revise the series anyway, so he can probably
> take care of the issue here in the new version as well. Something like this,
>
> memset(object, 0, s->object_size);
> memset(object, 0, s->size - s->inuse);
Looks like we also need to account for the redzone size. I'm testing
the fix right now.


--
Alexander Potapenko
Software Engineer

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