driver core: auxiliary bus: Fix auxiliary bus shutdown null auxdrv ptr

If the probe of the auxdrv failed, the device->driver is set to NULL.
During kernel shutdown, the bus shutdown will call auxdrv->shutdown and
cause an invalid ptr dereference. Add check to make sure device->driver is
not NULL before we proceed.

Fixes: 7de3697e9cbd ("Add auxiliary bus support")
Cc: Dave Ertman <[e-mail]>
Signed-off-by: Dave Jiang <[e-mail]>
Reviewed-by: Dan Williams <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/base/auxiliary.c

···
 
 static void auxiliary_bus_shutdown(struct device *dev)
 {
-	struct auxiliary_driver *auxdrv = to_auxiliary_drv(dev->driver);
-	struct auxiliary_device *auxdev = to_auxiliary_dev(dev);
+	struct auxiliary_driver *auxdrv = NULL;
+	struct auxiliary_device *auxdev;
 
-	if (auxdrv->shutdown)
+	if (dev->driver) {
+		auxdrv = to_auxiliary_drv(dev->driver);
+		auxdev = to_auxiliary_dev(dev);
+	}
+
+	if (auxdrv && auxdrv->shutdown)
 		auxdrv->shutdown(auxdev);
 }