ANDROID: binder: synchronize_rcu() when using POLLFREE.
commit 5eeb2ca02a2f6084fc57ae5c244a38baab07033a upstream. 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> Cc: stable <stable@vger.kernel.org> # 4.14+ Signed-off-by: Mattias Nissler <mnissler@chromium.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -2623,6 +2623,15 @@ static int binder_free_thread(struct binder_proc *proc,
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wake_up_poll(&thread->wait, POLLHUP | POLLFREE);
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}
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/*
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* This is needed to avoid races between wake_up_poll() above and
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* and ep_remove_waitqueue() called for other reasons (eg the epoll file
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* descriptor being closed); ep_remove_waitqueue() holds an RCU read
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* lock, so we can be sure it's done after calling synchronize_rcu().
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*/
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if (thread->looper & BINDER_LOOPER_STATE_POLL)
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synchronize_rcu();
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if (send_reply)
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binder_send_failed_reply(send_reply, BR_DEAD_REPLY);
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binder_release_work(&thread->todo);
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