USB: sierra: fix use after free at suspend/resume

Fix use after free or NULL-pointer dereference during suspend and
resume.

The port data may never have been allocated (port probe failed)
or may already have been released by port_remove (e.g. driver is
unloaded) when suspend and resume are called.

Fixes: e6929a9020ac ("USB: support for autosuspend in sierra while
online")

Cc: <stable@vger.kernel.org>	# v2.6.32
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/sierra.c

@@ -933,6 +933,7 @@ static int sierra_port_remove(struct usb_serial_port *port)
 	struct sierra_port_private *portdata;
 
 	portdata = usb_get_serial_port_data(port);
+	usb_set_serial_port_data(port, NULL);
 	kfree(portdata);
 
 	return 0;
@@ -949,6 +950,8 @@ static void stop_read_write_urbs(struct usb_serial *serial)
 	for (i = 0; i < serial->num_ports; ++i) {
 		port = serial->port[i];
 		portdata = usb_get_serial_port_data(port);
+		if (!portdata)
+			continue;
 		sierra_stop_rx_urbs(port);
 		usb_kill_anchored_urbs(&portdata->active);
 	}
@@ -991,6 +994,9 @@ static int sierra_resume(struct usb_serial *serial)
 		port = serial->port[i];
 		portdata = usb_get_serial_port_data(port);
 
+		if (!portdata)
+			continue;
+
 		while ((urb = usb_get_from_anchor(&portdata->delayed))) {
 			usb_anchor_urb(urb, &portdata->active);
 			intfdata->in_flight++;