static int packet_notifier(struct notifier_block *this,
			   unsigned long msg, void *ptr)
{
	struct sock *sk;
	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
	struct net *net = dev_net(dev);

	rcu_read_lock();
	sk_for_each_rcu(sk, &net->packet.sklist) {
		struct packet_sock *po = pkt_sk(sk);

		switch (msg) {
		case NETDEV_UNREGISTER:
			if (po->mclist)
				packet_dev_mclist_delete(dev, &po->mclist);
			/* fallthrough */

		case NETDEV_DOWN:
			if (dev->ifindex == po->ifindex) {
				spin_lock(&po->bind_lock);
				if (po->running) {
					__unregister_prot_hook(sk, false);
					sk->sk_err = ENETDOWN;
					if (!sock_flag(sk, SOCK_DEAD))
						sk->sk_error_report(sk);
				}
				if (msg == NETDEV_UNREGISTER) {
					packet_cached_dev_reset(po);
					fanout_release(sk);
					po->ifindex = -1;
					if (po->prot_hook.dev)
						dev_put(po->prot_hook.dev);
					po->prot_hook.dev = NULL;
				}
				spin_unlock(&po->bind_lock);
			}
			break;
		case NETDEV_UP:
			if (dev->ifindex == po->ifindex) {
				spin_lock(&po->bind_lock);
				if (po->num)
					register_prot_hook(sk);
				spin_unlock(&po->bind_lock);
			}
			break;
		}
	}
	rcu_read_unlock();
	return NOTIFY_DONE;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.