From: Martijn Coenen <maco@xxxxxxxxxxx> commit 5eeb2ca02a2f6084fc57ae5c244a38baab07033a upstream. To prevent races with ep_remove_waitqueue() removing the waitqueue at the same time. Reported-by: syzbot+a2a3c4909716e271487e@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Martijn Coenen <maco@xxxxxxxxxxx> Cc: stable <stable@xxxxxxxxxxxxxxx> # 4.14+ Signed-off-by: Mattias Nissler <mnissler@xxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/android/binder.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -2641,6 +2641,15 @@ static int binder_free_thread(struct bin wake_up_poll(&thread->wait, POLLHUP | POLLFREE); } + /* + * 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(&thread->todo);
