static int rtnl_net_newid(struct sk_buff *skb, struct nlmsghdr *nlh,
			  struct netlink_ext_ack *extack)
{
	struct net *net = sock_net(skb->sk);
	struct nlattr *tb[NETNSA_MAX + 1];
	struct nlattr *nla;
	struct net *peer;
	int nsid, err;

	err = nlmsg_parse(nlh, sizeof(struct rtgenmsg), tb, NETNSA_MAX,
			  rtnl_net_policy, extack);
	if (err < 0)
		return err;
	if (!tb[NETNSA_NSID]) {
		NL_SET_ERR_MSG(extack, "nsid is missing");
		return -EINVAL;
	}
	nsid = nla_get_s32(tb[NETNSA_NSID]);

	if (tb[NETNSA_PID]) {
		peer = get_net_ns_by_pid(nla_get_u32(tb[NETNSA_PID]));
		nla = tb[NETNSA_PID];
	} else if (tb[NETNSA_FD]) {
		peer = get_net_ns_by_fd(nla_get_u32(tb[NETNSA_FD]));
		nla = tb[NETNSA_FD];
	} else {
		NL_SET_ERR_MSG(extack, "Peer netns reference is missing");
		return -EINVAL;
	}
	if (IS_ERR(peer)) {
		NL_SET_BAD_ATTR(extack, nla);
		NL_SET_ERR_MSG(extack, "Peer netns reference is invalid");
		return PTR_ERR(peer);
	}

	spin_lock_bh(&net->nsid_lock);
	if (__peernet2id(net, peer) >= 0) {
		spin_unlock_bh(&net->nsid_lock);
		err = -EEXIST;
		NL_SET_BAD_ATTR(extack, nla);
		NL_SET_ERR_MSG(extack,
			       "Peer netns already has a nsid assigned");
		goto out;
	}

	err = alloc_netid(net, peer, nsid);
	spin_unlock_bh(&net->nsid_lock);
	if (err >= 0) {
		rtnl_net_notifyid(net, RTM_NEWNSID, err);
		err = 0;
	} else if (err == -ENOSPC && nsid >= 0) {
		err = -EEXIST;
		NL_SET_BAD_ATTR(extack, tb[NETNSA_NSID]);
		NL_SET_ERR_MSG(extack, "The specified nsid is already used");
	}
out:
	put_net(peer);
	return err;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.