[PATCH] binder: fix race between munmap() and direct reclaim

[Joel Fernandes]

On Sat, Mar 02, 2019 at 08:27:44AM -0800, Todd Kjos wrote:
> On Fri, Mar 1, 2019 at 11:57 PM Greg KH <gregkh at linuxfoundation.org> wrote:
> >
> > On Fri, Mar 01, 2019 at 03:06:06PM -0800, Todd Kjos wrote:
> > > An munmap() on a binder device causes binder_vma_close() to be called
> > > which clears the alloc->vma pointer.
> > >
> > > If direct reclaim causes binder_alloc_free_page() to be called, there
> > > is a race where alloc->vma is read into a local vma pointer and then
> > > used later after the mm->mmap_sem is acquired. This can result in
> > > calling zap_page_range() with an invalid vma which manifests as a
> > > use-after-free in zap_page_range().
> > >
> > > The fix is to check alloc->vma after acquiring the mmap_sem (which we
> > > were acquiring anyway) and skip zap_page_range() if it has changed
> > > to NULL.
> > >
> > > Signed-off-by: Todd Kjos <tkjos at google.com>

Awesome patch, 
Reviewed-by: Joel Fernandes (Google) <joel at joelfernandes.org>

thanks!
 
 - Joel

> > > ---
> >
> > Any specific commit that this fixes?
> 
> No, it's been there a long time.
> 
> > And should it be marked for stable releases?
> 
> It is needed in stable (back to 4.4), but will need to be backported.
> Should I post backported versions targeting the specific releases now?
> I was thinking we'd wait for this one to land. I think we'll need 1
> patch for 4.4/4.9 and a second one for 4.14/4.19 (and some of those
> backported patches will have conflicts when merged down to android-4.X
> -- I think the 4.14/4.19 version will apply to all the android
> branches). Let me know how you want to handle this.
> 
> >
> > thanks,
> >
> > greg k-h