From: Martijn Coenen maco@android.com

binder_poll() passes the thread->wait waitqueue that can be slept on for work. When a thread that uses epoll explicitly exits using BINDER_THREAD_EXIT, the waitqueue is freed, but it is never removed from the corresponding epoll data structure. When the process subsequently exits, the epoll cleanup code tries to access the waitlist, which results in a use-after-free.

Prevent this by using POLLFREE when the thread exits.

Signed-off-by: Martijn Coenen maco@android.com Reported-by: syzbot syzkaller@googlegroups.com Cc: stable stable@vger.kernel.org # 4.14 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/android/binder.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c index c96623d..77b1b95 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -4269,6 +4269,18 @@ static int binder_thread_release(struct binder_proc *proc, if (t) spin_lock(&t->lock); } + + /* + * If this thread used poll, make sure we remove the waitqueue + * from any epoll data structures holding it with POLLFREE. + * waitqueue_active() is safe to use here because we're holding + * the inner lock. + */ + if ((thread->looper & BINDER_LOOPER_STATE_POLL) && + waitqueue_active(&thread->wait)) { + wake_up_poll(&thread->wait, POLLHUP | POLLFREE); + } + binder_inner_proc_unlock(thread->proc);

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