[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.

This patch was already included in Linus' tree.
Signed-off-by: Horst Schirmeier <horst@schirmeier.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Adrian Bunk <bunk@stusta.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
 
-	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 (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,