[PATCH] USB: usbcore: usb_set_configuration oops (NULL ptr dereference)

When trying to deconfigure a device via usb_set_configuration(dev, 0),
2.6.16-rc kernels after 55c52718 oops
with "Unable to handle NULL pointer dereference at...". This is due to
an unchecked dereference of cp in the power budget part.
Signed-off-by: NHorst Schirmeier <horst@schirmeier.com>
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/message.c

@@ -1388,11 +1388,13 @@ int usb_set_configuration(struct usb_device *dev, int configuration)
 	if (dev->state != USB_STATE_ADDRESS)
 		usb_disable_device (dev, 1);	// Skip ep0
 
+	if (cp) {
 		i = dev->bus_mA - cp->desc.bMaxPower * 2;
 		if (i < 0)
 			dev_warn(&dev->dev, "new config #%d exceeds power "
 					"limit by %dmA\n",
 					configuration, -i);
+	}
 
 	if ((ret = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
 			USB_REQ_SET_CONFIGURATION, 0, configuration, 0,