patch "ANDROID: binder: remove waitqueue when thread exits." added to char-misc-testing

[<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 my char-misc git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-testing branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will be merged to the char-misc-next branch sometime soon,
after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.


>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.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/android/binder.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 82fcc1e64e82..de4b67f09ddb 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -4365,6 +4365,18 @@ static int binder_thread_release(struct binder_proc *proc,
 		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)
-- 
2.15.1