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 Cc: stable stable@vger.kernel.org # 4.14 [backport BINDER_LOOPER_STATE_POLL logic as well] Signed-off-by: Mattias Nissler mnissler@chromium.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/android/binder.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)
--- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -334,7 +334,8 @@ enum { BINDER_LOOPER_STATE_EXITED = 0x04, BINDER_LOOPER_STATE_INVALID = 0x08, BINDER_LOOPER_STATE_WAITING = 0x10, - BINDER_LOOPER_STATE_NEED_RETURN = 0x20 + BINDER_LOOPER_STATE_NEED_RETURN = 0x20, + BINDER_LOOPER_STATE_POLL = 0x40, };
struct binder_thread { @@ -2610,6 +2611,18 @@ static int binder_free_thread(struct bin } else BUG(); } + + /* + * 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); + } + if (send_reply) binder_send_failed_reply(send_reply, BR_DEAD_REPLY); binder_release_work(&thread->todo); @@ -2633,6 +2646,8 @@ static unsigned int binder_poll(struct f return POLLERR; }
+ thread->looper |= BINDER_LOOPER_STATE_POLL; + wait_for_proc_work = thread->transaction_stack == NULL && list_empty(&thread->todo) && thread->return_error == BR_OK;