In the Linux kernel, the following vulnerability has been resolved:
rust_binder: call set_notification_done() without proc lock
Consider the following sequence of events on a death listener:
- The remote process dies and sends a BR_DEAD_BINDER message.
- The local process invokes the BC_CLEAR_DEATH_NOTIFICATION command.
- The local process then invokes the BC_DEAD_BINDER_DONE.
However, this can result in a deadlock if the current thread is not a looper. This is because dead_binder_done() still holds the proc lock during set_notification_done(), which called push_work_if_looper(). Normally, push_work_if_looper() takes the thread lock, which is fine to take under the proc lock. But if the current thread is not a looper, then it falls back to delivering the reply to the process work queue, which involves taking the proc lock. Since the proc lock is already held, this is a deadlock.
Fix this by releasing the proc lock during set_notification_done(). It was not intentional that it was held during that function to begin with.
I don't think this ever happens in Android because BC_DEAD_BINDER_DONE is only invoked in response to BR_DEAD_BINDER messages, and the kernel always delivers BR_DEAD_BINDER to a looper. So there's no scenario where Android userspace will call BC_DEAD_BINDER_DONE on a non-looper thread.