[PATCH 4.18 054/145] net/9p/trans_fd.c: fix race-condition by flushing workqueue before the kfree()

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tomas Bortoli <tomasbortoli@xxxxxxxxx>

commit 430ac66eb4c5b5c4eb846b78ebf65747510b30f1 upstream.

The patch adds the flush in p9_mux_poll_stop() as it the function used by
p9_conn_destroy(), in turn called by p9_fd_close() to stop the async
polling associated with the data regarding the connection.

Link: http://lkml.kernel.org/r/20180720092730.27104-1-tomasbortoli@xxxxxxxxx
Signed-off-by: Tomas Bortoli <tomasbortoli@xxxxxxxxx>
Reported-by: syzbot+39749ed7d9ef6dfb23f6@xxxxxxxxxxxxxxxxxxxxxxxxx
To: Eric Van Hensbergen <ericvh@xxxxxxxxx>
To: Ron Minnich <rminnich@xxxxxxxxxx>
To: Latchesar Ionkov <lucho@xxxxxxxxxx>
Cc: Yiwen Jiang <jiangyiwen@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Dominique Martinet <dominique.martinet@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/9p/trans_fd.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -185,6 +185,8 @@ static void p9_mux_poll_stop(struct p9_c
 	spin_lock_irqsave(&p9_poll_lock, flags);
 	list_del_init(&m->poll_pending_link);
 	spin_unlock_irqrestore(&p9_poll_lock, flags);
+
+	flush_work(&p9_poll_work);
 }
 
 /**