static int packet_dev_mc(struct net_device *dev, struct packet_mclist *i,
			 int what)
{
	switch (i->type) {
	case PACKET_MR_MULTICAST:
		if (i->alen != dev->addr_len)
			return -EINVAL;
		if (what > 0)
			return dev_mc_add(dev, i->addr);
		else
			return dev_mc_del(dev, i->addr);
		break;
	case PACKET_MR_PROMISC:
		return dev_set_promiscuity(dev, what);
	case PACKET_MR_ALLMULTI:
		return dev_set_allmulti(dev, what);
	case PACKET_MR_UNICAST:
		if (i->alen != dev->addr_len)
			return -EINVAL;
		if (what > 0)
			return dev_uc_add(dev, i->addr);
		else
			return dev_uc_del(dev, i->addr);
		break;
	default:
		break;
	}
	return 0;
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.