USB: serial: keyspan_pda: fix write-wakeup use-after-free

The driver's deferred write wakeup was never flushed on disconnect,
something which could lead to the driver port data being freed while the
wakeup work is still scheduled.

Fix this by using the usb-serial write wakeup which gets cancelled
properly on disconnect.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/keyspan_pda.c

@@ -43,8 +43,7 @@
 struct keyspan_pda_private {
 	int			tx_room;
 	int			tx_throttled;
-	struct work_struct			wakeup_work;
-	struct work_struct			unthrottle_work;
+	struct work_struct	unthrottle_work;
 	struct usb_serial	*serial;
 	struct usb_serial_port	*port;
 };
@@ -97,15 +96,6 @@ static const struct usb_device_id id_table_fake_xircom[] = {
 };
 #endif
 
-static void keyspan_pda_wakeup_write(struct work_struct *work)
-{
-	struct keyspan_pda_private *priv =
-		container_of(work, struct keyspan_pda_private, wakeup_work);
-	struct usb_serial_port *port = priv->port;
-
-	tty_port_tty_wakeup(&port->port);
-}
-
 static void keyspan_pda_request_unthrottle(struct work_struct *work)
 {
 	struct keyspan_pda_private *priv =
@@ -183,7 +173,7 @@ static void keyspan_pda_rx_interrupt(struct urb *urb)
 		case 2: /* tx unthrottle interrupt */
 			priv->tx_throttled = 0;
 			/* queue up a wakeup at scheduler time */
-			schedule_work(&priv->wakeup_work);
+			usb_serial_port_softint(port);
 			break;
 		default:
 			break;
@@ -563,7 +553,7 @@ static void keyspan_pda_write_bulk_callback(struct urb *urb)
 	priv = usb_get_serial_port_data(port);
 
 	/* queue up a wakeup at scheduler time */
-	schedule_work(&priv->wakeup_work);
+	usb_serial_port_softint(port);
 }
 
 
@@ -715,7 +705,6 @@ static int keyspan_pda_port_probe(struct usb_serial_port *port)
 	if (!priv)
 		return -ENOMEM;
 
-	INIT_WORK(&priv->wakeup_work, keyspan_pda_wakeup_write);
 	INIT_WORK(&priv->unthrottle_work, keyspan_pda_request_unthrottle);
 	priv->serial = port->serial;
 	priv->port = port;