Patch "ANDROID: binder: remove waitqueue when thread exits." has been added to the 4.14-stable tree

[<gregkh@linuxfoundation.org>]

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;a=summary

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