Re: [PATCH v2 0/5] mm/slub: Improve data handling of krealloc() when orig_size is enabled

[Feng Tang]

On Fri, Oct 04, 2024 at 05:52:10PM +0800, Vlastimil Babka wrote:
> On 10/4/24 11:18, Vlastimil Babka wrote:
> > On 10/4/24 08:44, Marco Elver wrote:
> > 
> > I think it's commit d0a38fad51cc7 doing in __do_krealloc()
> > 
> > -               ks = ksize(p);
> > +
> > +               s = virt_to_cache(p);
> > +               orig_size = get_orig_size(s, (void *)p);
> > +               ks = s->object_size;
> > 
> > so for kfence objects we don't get their actual allocation size but the
> > potentially larger bucket size?
> > 
> > I guess we could do:
> > 
> > ks = kfence_ksize(p) ?: s->object_size;
> > 
> > ?
> 
> Hmm this probably is not the whole story, we also have:
> 
> -               memcpy(ret, kasan_reset_tag(p), ks);
> +               if (orig_size)
> +                       memcpy(ret, kasan_reset_tag(p), orig_size);
> 
> orig_size for kfence will be again s->object_size so the memcpy might be a
> (read) buffer overflow from a kfence allocation.
> 
> I think get_orig_size() should perhaps return kfence_ksize(p) for kfence
> allocations, in addition to the change above.
> 
> Or alternatively we don't change get_orig_size() (in a different commit) at
> all, but __do_krealloc() will have an "if is_kfence_address()" that sets
> both orig_size and ks to kfence_ksize(p) appropriately. That might be easier
> to follow.
> 
> But either way means rewriting 2 commits. I think it's indeed better to drop
> the series now from -next and submit a v3.

Yes, we can revert now. Sorry for the inconvenience.

Thanks,
Feng