Re: [PATCH v6 0/5] mm: Unconditional per-VMA locks and cleanups

[Carlos Llamas <cmllamas@google.com>]

On Mon, Aug 31, 2026 at 11:13:16AM +0000, Alice Ryhl wrote:
> On Sat, Aug 29, 2026 at 06:56:25PM -0700, Andrew Morton wrote:
> > On Thu, 13 Aug 2026 12:34:28 -0700 Suren Baghdasaryan <surenb@google.com> wrote:
> > 
> > > v2 version of this patchset [1] was written by Dave Hansen and per his
> > > request, I'm taking over this series.
> > > 
> > > tl;dr: Make per-VMA locks available in all configs. Simplify some
> > > of the per-VMA lock users now that they can rely on them being
> > > always available.
> > 
> > It's been 2+ weeks so perhaps a refresh-and-remind would be helpful.
> > 
> > But it applies well enough and is adequately reviewed so I put it in
> > there for testing, thanks.
> > 
> > AI review might have found a couple of pre-existing binder bugs:
> > 
> > 	https://sashiko.dev/#/patchset/20260813193433.3318288-1-surenb@google.com
> > 
> > and a small rusty thing which you might wish to attend to.
> 
> The binder bug is not actually a bug. When using VM_MIXEDMAP and
> vm_insert_page(), the vma takes a refcount on the page, so there is no
> use-after-free even if free_page() is invoked without removing it from
> the vma.

Exactly! I agree the refcount on the page would prevent the UAF.

However, we should still reject mremap() because this leaves the page in
limbo since it is not given back to the shrinker and also binder can't
make use of it anymore. I'll send out a patch to fix this.

Thanks,
--
Carlos Llamas