staging: gpib: Fix NULL pointer dereference in detach

When the detach function is called after a failed attach
the usb_dev initialization can cause a NULL pointer
dereference. This happens when the usb device is not found
in the attach procedure.

Remove the usb_dev variable and initialization and change the dev
in the dev_info message from the usb_dev to the gpib_dev.

Fixes: fbae709 ("staging: gpib: Update messaging and usb_device refs in agilent_usb")
Signed-off-by: Dave Penkler <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: dpenkler

drivers/staging/gpib/agilent_82357a/agilent_82357a.c

@@ -1442,12 +1442,10 @@ static int agilent_82357a_go_idle(gpib_board_t *board)
 static void agilent_82357a_detach(gpib_board_t *board)
 {
 	struct agilent_82357a_priv *a_priv;
-	struct usb_device *usb_dev;
 
 	mutex_lock(&agilent_82357a_hotplug_lock);
 
 	a_priv = board->private_data;
-	usb_dev = interface_to_usbdev(a_priv->bus_interface);
 	if (a_priv) {
 		if (a_priv->bus_interface) {
 			agilent_82357a_go_idle(board);
@@ -1459,7 +1457,7 @@ static void agilent_82357a_detach(gpib_board_t *board)
 		agilent_82357a_cleanup_urbs(a_priv);
 		agilent_82357a_free_private(a_priv);
 	}
-	dev_info(&usb_dev->dev, "%s: detached\n", __func__);
+	dev_info(board->gpib_dev, "%s: detached\n", __func__);
 	mutex_unlock(&agilent_82357a_hotplug_lock);
 }