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

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Apr 24, 2019 at 10:35:56AM -0700, Todd Kjos wrote:
> From: Todd Kjos <tkjos@android.com>
> 
> commit 5cec2d2e5839f9c0fec319c523a911e0a7fd299f upstream.
> 
> 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@google.com>
> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> Cc: stable <stable@vger.kernel.org> # 5.0, 4.19, 4.14
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> Greg: This applies to 5.0, 4.19, 4.14. Not needed before 4.12.

Thanks, now queued up.

greg k-h