greybus: es1/2: fix use-after-free in completion callback

Reset the hcpriv field before returning the message to greybus core in
the OUT-URB completion callback.

This fixes a use-after-free bug when sending responses to incoming
requests as the final reference is then dropped when the message is
returned.
Reported-by: Michael Scott <michael.scott@linaro.org>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/es1.c

@@ -397,16 +397,16 @@ static void cport_out_callback(struct urb *urb)
 
 	gb_message_cport_clear(message->header);
 
+	spin_lock_irqsave(&es1->cport_out_urb_lock, flags);
+	message->hcpriv = NULL;
+	spin_unlock_irqrestore(&es1->cport_out_urb_lock, flags);
+
 	/*
 	 * Tell the submitter that the message send (attempt) is
 	 * complete, and report the status.
 	 */
 	greybus_message_sent(hd, message, status);
 
-	spin_lock_irqsave(&es1->cport_out_urb_lock, flags);
-	message->hcpriv = NULL;
-	spin_unlock_irqrestore(&es1->cport_out_urb_lock, flags);
-
 	free_urb(es1, urb);
 }
 

drivers/staging/greybus/es2.c

@@ -506,16 +506,16 @@ static void cport_out_callback(struct urb *urb)
 
 	gb_message_cport_clear(message->header);
 
+	spin_lock_irqsave(&es1->cport_out_urb_lock, flags);
+	message->hcpriv = NULL;
+	spin_unlock_irqrestore(&es1->cport_out_urb_lock, flags);
+
 	/*
 	 * Tell the submitter that the message send (attempt) is
 	 * complete, and report the status.
 	 */
 	greybus_message_sent(hd, message, status);
 
-	spin_lock_irqsave(&es1->cport_out_urb_lock, flags);
-	message->hcpriv = NULL;
-	spin_unlock_irqrestore(&es1->cport_out_urb_lock, flags);
-
 	free_urb(es1, urb);
 }