static int do_mq_notify(mqd_t mqdes, const struct sigevent *notification)
{
	int ret;
	struct fd f;
	struct sock *sock;
	struct inode *inode;
	struct mqueue_inode_info *info;
	struct sk_buff *nc;

	audit_mq_notify(mqdes, notification);

	nc = NULL;
	sock = NULL;
	if (notification != NULL) {
		if (unlikely(notification->sigev_notify != SIGEV_NONE &&
			     notification->sigev_notify != SIGEV_SIGNAL &&
			     notification->sigev_notify != SIGEV_THREAD))
			return -EINVAL;
		if (notification->sigev_notify == SIGEV_SIGNAL &&
			!valid_signal(notification->sigev_signo)) {
			return -EINVAL;
		}
		if (notification->sigev_notify == SIGEV_THREAD) {
			long timeo;

			/* create the notify skb */
			nc = alloc_skb(NOTIFY_COOKIE_LEN, GFP_KERNEL);
			if (!nc) {
				ret = -ENOMEM;
				goto out;
			}
			if (copy_from_user(nc->data,
					notification->sigev_value.sival_ptr,
					NOTIFY_COOKIE_LEN)) {
				ret = -EFAULT;
				goto out;
			}

			/* TODO: add a header? */
			skb_put(nc, NOTIFY_COOKIE_LEN);
			/* and attach it to the socket */
retry:
			f = fdget(notification->sigev_signo);
			if (!f.file) {
				ret = -EBADF;
				goto out;
			}
			sock = netlink_getsockbyfilp(f.file);
			fdput(f);
			if (IS_ERR(sock)) {
				ret = PTR_ERR(sock);
				sock = NULL;
				goto out;
			}
 
 			timeo = MAX_SCHEDULE_TIMEOUT;
 			ret = netlink_attachskb(sock, nc, &timeo, NULL);
			if (ret == 1) {
				sock = NULL;
 				goto retry;
			}
 			if (ret) {
 				sock = NULL;
 				nc = NULL;
				goto out;
			}
		}
	}

	f = fdget(mqdes);
	if (!f.file) {
		ret = -EBADF;
		goto out;
	}

	inode = file_inode(f.file);
	if (unlikely(f.file->f_op != &mqueue_file_operations)) {
		ret = -EBADF;
		goto out_fput;
	}
	info = MQUEUE_I(inode);

	ret = 0;
	spin_lock(&info->lock);
	if (notification == NULL) {
		if (info->notify_owner == task_tgid(current)) {
			remove_notification(info);
			inode->i_atime = inode->i_ctime = current_time(inode);
		}
	} else if (info->notify_owner != NULL) {
		ret = -EBUSY;
	} else {
		switch (notification->sigev_notify) {
		case SIGEV_NONE:
			info->notify.sigev_notify = SIGEV_NONE;
			break;
		case SIGEV_THREAD:
			info->notify_sock = sock;
			info->notify_cookie = nc;
			sock = NULL;
			nc = NULL;
			info->notify.sigev_notify = SIGEV_THREAD;
			break;
		case SIGEV_SIGNAL:
			info->notify.sigev_signo = notification->sigev_signo;
			info->notify.sigev_value = notification->sigev_value;
			info->notify.sigev_notify = SIGEV_SIGNAL;
			break;
		}

		info->notify_owner = get_pid(task_tgid(current));
		info->notify_user_ns = get_user_ns(current_user_ns());
		inode->i_atime = inode->i_ctime = current_time(inode);
	}
	spin_unlock(&info->lock);
out_fput:
	fdput(f);
out:
	if (sock)
		netlink_detachskb(sock, nc);
	else if (nc)
		dev_kfree_skb(nc);

	return ret;
}

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.