can: peak: fix bad memory access and free sequence

commit b67d0dd7d0dc9e456825447bbeb935d8ef43ea7c upstream.

Fix for bad memory access while disconnecting. netdev is freed before
private data free, and dev is accessed after freeing netdev.

This makes a slub problem, and it raise kernel oops with slub debugger
config.

Signed-off-by: Jiho Chu <jiho.chu@samsung.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: jihochu

drivers/net/can/usb/peak_usb/pcan_usb_core.c

@@ -872,23 +872,25 @@ static int peak_usb_create_dev(const struct peak_usb_adapter *peak_usb_adapter,
 static void peak_usb_disconnect(struct usb_interface *intf)
 {
 	struct peak_usb_device *dev;
+	struct peak_usb_device *dev_prev_siblings;
 
 	/* unregister as many netdev devices as siblings */
-	for (dev = usb_get_intfdata(intf); dev; dev = dev->prev_siblings) {
+	for (dev = usb_get_intfdata(intf); dev; dev = dev_prev_siblings) {
 		struct net_device *netdev = dev->netdev;
 		char name[IFNAMSIZ];
 
+		dev_prev_siblings = dev->prev_siblings;
 		dev->state &= ~PCAN_USB_STATE_CONNECTED;
 		strncpy(name, netdev->name, IFNAMSIZ);
 
 		unregister_netdev(netdev);
-		free_candev(netdev);
 
 		kfree(dev->cmd_buf);
 		dev->next_siblings = NULL;
 		if (dev->adapter->dev_free)
 			dev->adapter->dev_free(dev);
 
+		free_candev(netdev);
 		dev_info(&intf->dev, "%s removed\n", name);
 	}