caif_usb: Check driver name before reading driver state in netdev notifier

In cfusbl_device_notify(), the usbnet and usbdev variables are
initialised before the driver name has been checked.  In case the
device's driver is not cdc_ncm, this may result in reading beyond the
end of the netdev private area.  Move the initialisation below the
driver name check.
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/caif/caif_usb.c

@@ -126,8 +126,8 @@ static int cfusbl_device_notify(struct notifier_block *me, unsigned long what,
 	struct net_device *dev = arg;
 	struct caif_dev_common common;
 	struct cflayer *layer, *link_support;
-	struct usbnet	*usbnet = netdev_priv(dev);
-	struct usb_device	*usbdev = usbnet->udev;
+	struct usbnet *usbnet;
+	struct usb_device *usbdev;
 	struct ethtool_drvinfo drvinfo;
 
 	/*
@@ -141,6 +141,9 @@ static int cfusbl_device_notify(struct notifier_block *me, unsigned long what,
 	if (strncmp(drvinfo.driver, "cdc_ncm", 7) != 0)
 		return 0;
 
+	usbnet = netdev_priv(dev);
+	usbdev = usbnet->udev;
+
 	pr_debug("USB CDC NCM device VID:0x%4x PID:0x%4x\n",
 		le16_to_cpu(usbdev->descriptor.idVendor),
 		le16_to_cpu(usbdev->descriptor.idProduct));