This is a note to let you know that I've just added the patch titled

ANDROID: binder: remove waitqueue when thread exits.

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: android-binder-remove-waitqueue-when-thread-exits.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From f5cb779ba16334b45ba8946d6bfa6d9834d1527f Mon Sep 17 00:00:00 2001

From: Martijn Coenen maco@android.com Date: Fri, 5 Jan 2018 11:27:07 +0100 Subject: ANDROID: binder: remove waitqueue when thread exits.

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)

Patches currently in stable-queue which might be from maco@android.com are

queue-4.14/android-binder-remove-waitqueue-when-thread-exits.patch queue-4.14/android-binder-use-vm_alloc-to-get-vm-area.patch