Patch "ANDROID: binder: synchronize_rcu() when using POLLFREE." has been added to the 4.15-stable tree

[<gregkh@linuxfoundation.org>]

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

    ANDROID: binder: synchronize_rcu() when using POLLFREE.

to the 4.15-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-synchronize_rcu-when-using-pollfree.patch
and it can be found in the queue-4.15 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 5eeb2ca02a2f6084fc57ae5c244a38baab07033a Mon Sep 17 00:00:00 2001
From: Martijn Coenen <maco@android.com>
Date: Fri, 16 Feb 2018 09:47:15 +0100
Subject: ANDROID: binder: synchronize_rcu() when using POLLFREE.

From: Martijn Coenen <maco@android.com>

commit 5eeb2ca02a2f6084fc57ae5c244a38baab07033a upstream.

To prevent races with ep_remove_waitqueue() removing the
waitqueue at the same time.

Reported-by: syzbot+a2a3c4909716e271487e@syzkaller.appspotmail.com
Signed-off-by: Martijn Coenen <maco@android.com>
Cc: stable <stable@vger.kernel.org> # 4.14+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/android/binder.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -4322,6 +4322,15 @@ static int binder_thread_release(struct
 
 	binder_inner_proc_unlock(thread->proc);
 
+	/*
+	 * This is needed to avoid races between wake_up_poll() above and
+	 * and ep_remove_waitqueue() called for other reasons (eg the epoll file
+	 * descriptor being closed); ep_remove_waitqueue() holds an RCU read
+	 * lock, so we can be sure it's done after calling synchronize_rcu().
+	 */
+	if (thread->looper & BINDER_LOOPER_STATE_POLL)
+		synchronize_rcu();
+
 	if (send_reply)
 		binder_send_failed_reply(send_reply, BR_DEAD_REPLY);
 	binder_release_work(proc, &thread->todo);


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

queue-4.15/android-binder-synchronize_rcu-when-using-pollfree.patch