Re: [PATCH] binder: fix race that allows malicious free of live buffer

Todd Kjos
2018-11-10T02:04:14Z

On Fri, Nov 9, 2018 at 4:32 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Tue, Nov 06, 2018 at 03:55:32PM -0800, Todd Kjos wrote:
> > Malicious code can attempt to free buffers using the
> > BC_FREE_BUFFER ioctl to binder. There are protections
> > against a user freeing a buffer while in use by the
> > kernel, however there was a window where BC_FREE_BUFFER
> > could be used to free a recently allocated buffer that
> > was not completely initialized. This resulted in a
> > use-after-free detected by KASAN with a malicious
> > test program.
> >
> > This window is closed by setting the buffer's
> > allow_user_free attribute to 0 when the buffer
> > is allocated or when the user has previously
> > freed it instead of waiting for the caller
> > to set it. The problem was that when the struct
> > buffer was recycled, allow_user_free was stale
> > and set to 1 allowing a free to go through.
> >
> > Signed-off-by: Todd Kjos <tkjos@google.com>
> > Acked-by: Arve Hjønnevåg <arve@android.com>
>
> No "stable" tag here? Any idea how far back the stable backporting
> should go, if any?

Sorry about that. It should be backported to 4.14 and later.

>
> thanks,
>
> greg k-h