[PATCH 3.16 284/306] can: peak: fix bad memory access and free sequence

[Ben Hutchings]

3.16.40-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: ììí <jiho.chu@xxxxxxxxxxx>

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@xxxxxxxxxxx>
Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/net/can/usb/peak_usb/pcan_usb_core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/net/can/usb/peak_usb/pcan_usb_core.c
+++ b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
@@ -826,23 +826,25 @@ lbl_free_candev:
 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);
 	}