static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf,
			struct file *file, unsigned int cmd, unsigned long arg)
{
	int unit, err = -EFAULT;
	struct ppp *ppp;
	struct channel *chan;
	struct ppp_net *pn;
	int __user *p = (int __user *)arg;

	switch (cmd) {
	case PPPIOCNEWUNIT:
		/* Create a new ppp unit */
		if (get_user(unit, p))
			break;
		ppp = ppp_create_interface(net, unit, file, &err);
		if (!ppp)
			break;
		file->private_data = &ppp->file;
		err = -EFAULT;
		if (put_user(ppp->file.index, p))
			break;
		err = 0;
		break;

	case PPPIOCATTACH:
		/* Attach to an existing ppp unit */
		if (get_user(unit, p))
			break;
		err = -ENXIO;
		pn = ppp_pernet(net);
		mutex_lock(&pn->all_ppp_mutex);
		ppp = ppp_find_unit(pn, unit);
		if (ppp) {
			atomic_inc(&ppp->file.refcnt);
			file->private_data = &ppp->file;
			err = 0;
		}
		mutex_unlock(&pn->all_ppp_mutex);
		break;

	case PPPIOCATTCHAN:
		if (get_user(unit, p))
			break;
		err = -ENXIO;
		pn = ppp_pernet(net);
		spin_lock_bh(&pn->all_channels_lock);
		chan = ppp_find_channel(pn, unit);
		if (chan) {
			atomic_inc(&chan->file.refcnt);
			file->private_data = &chan->file;
			err = 0;
		}
		spin_unlock_bh(&pn->all_channels_lock);
		break;

	default:
		err = -ENOTTY;
	}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.