From 80eb98a4ee70428d5b4b7202195a916385a76809 Mon Sep 17 00:00:00 2001 From: Martijn Coenen Date: Fri, 5 Jan 2018 11:27:07 +0100 Subject: ANDROID: binder: remove waitqueue when thread exits. 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 Reported-by: syzbot Cc: stable # 4.14 [backport BINDER_LOOPER_STATE_POLL logic as well] Signed-off-by: Mattias Nissler Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) (limited to 'drivers/android') diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 01eb2a2a3746..5c13a6eb4fea 100644 --- 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 binder_proc *proc, } 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 global 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 file *filp, 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; -- cgit v1.2.3