static struct net_device *netdev_next_lower_dev(struct net_device *dev,
						struct list_head **iter)
{
	struct netdev_adjacent *lower;

	lower = list_entry((*iter)->next, struct netdev_adjacent, list);

	if (&lower->list == &dev->adj_list.lower)
		return NULL;

	*iter = &lower->list;

	return lower->dev;
}

The product dereferences a pointer that it expects to be valid but is NULL.