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SubjectRe: [PATCH] ANDROID: binder: synchronize_rcu() when using POLLFREE.
Greg,

This is for 4.14 LTS and 4.16.

Thanks,
Martijn

On Fri, Feb 16, 2018 at 9:47 AM, Martijn Coenen <maco@android.com> wrote:
> To prevent races with ep_remove_waitqueue() removing the
> waitqueue at the same time.
>
> Reported-by: syzbot+a2a3c4909716e271487e@syzkaller.appspotmail.com
> Signed-off-by: Martijn Coenen <maco@android.com>
> ---
> drivers/android/binder.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index 15e3d3c2260d..359220f87e1d 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -4376,6 +4376,15 @@ static int binder_thread_release(struct binder_proc *proc,
>
> binder_inner_proc_unlock(thread->proc);
>
> + /*
> + * This is needed to avoid races between wake_up_poll() above and
> + * and ep_remove_waitqueue() called for other reasons (eg the epoll file
> + * descriptor being closed); ep_remove_waitqueue() holds an RCU read
> + * lock, so we can be sure it's done after calling synchronize_rcu().
> + */
> + if (thread->looper & BINDER_LOOPER_STATE_POLL)
> + synchronize_rcu();
> +
> if (send_reply)
> binder_send_failed_reply(send_reply, BR_DEAD_REPLY);
> binder_release_work(proc, &thread->todo);
> --
> 2.16.1.291.g4437f3f132-goog
>

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