4.14-stable review patch. If anyone has any objections, please let me know.
------------------
From: Martijn Coenen maco@android.com
commit f5cb779ba16334b45ba8946d6bfa6d9834d1527f upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/android/binder.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
--- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -4302,6 +4302,18 @@ static int binder_thread_release(struct 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);
if (send_reply)