Re: [PATCH v2 1/1] mm: fix use-after-free when anon vma name is used after vma is freed

[Suren Baghdasaryan <surenb@google.com>]

On Thu, Feb 10, 2022 at 5:27 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Wed, Feb 09, 2022 at 08:32:15PM -0800, Suren Baghdasaryan wrote:
> > +void vma_anon_name_put(struct anon_vma_name *anon_name)
> > +{
> > +     kref_put(&anon_name->kref, vma_anon_name_free);
> > +}
>
> To agree with Michal, make this:
>
>         if (anon_name)
>                 kref_put(&anon_name->kref, vma_anon_name_free);

Ack.

>
> >
> > -     error = madvise_update_vma(vma, prev, start, end, new_flags,
> > -                                vma_anon_name(vma));
> > +     anon_name = vma_anon_name_get(vma);
> > +     if (anon_name) {
> > +             error = madvise_update_vma(vma, prev, start, end, new_flags,
> > +                                        anon_name->name);
> > +             vma_anon_name_put(anon_name);
> > +     } else {
> > +             error = madvise_update_vma(vma, prev, start, end, new_flags,
> > +                                        NULL);
> > +     }
>
> And then this becomes:
>
>         anon_name = vma_anon_name_get(vma);
>         error = madvise_update_vma(vma, prev, start, end, new_flags, anon_name);
>         vma_anon_name_put(anon_name);

As I indicated in the other reply, there is another madvise_update_vma
user which has only the name string, not the anon_vma_name struct. So
this can become:

   anon_name = vma_anon_name_get(vma);
   error = madvise_update_vma(vma, prev, start, end, new_flags,
                                                   anon_name ?
anon_name->name : NULL);
   vma_anon_name_put(anon_name);