struct ion_client *ion_client_create(struct ion_device *dev,
				     const char *name)
{
	struct ion_client *client;
	struct task_struct *task;
	struct rb_node **p;
	struct rb_node *parent = NULL;
	struct ion_client *entry;
	pid_t pid;

	if (!name) {
		pr_err("%s: Name cannot be null\n", __func__);
		return ERR_PTR(-EINVAL);
	}

	get_task_struct(current->group_leader);
	task_lock(current->group_leader);
	pid = task_pid_nr(current->group_leader);
	/*
	 * don't bother to store task struct for kernel threads,
	 * they can't be killed anyway
	 */
	if (current->group_leader->flags & PF_KTHREAD) {
		put_task_struct(current->group_leader);
		task = NULL;
	} else {
		task = current->group_leader;
	}
	task_unlock(current->group_leader);

	client = kzalloc(sizeof(struct ion_client), GFP_KERNEL);
	if (!client)
		goto err_put_task_struct;

	client->dev = dev;
	client->handles = RB_ROOT;
	idr_init(&client->idr);
	mutex_init(&client->lock);
	client->task = task;
	client->pid = pid;
	client->name = kstrdup(name, GFP_KERNEL);
	if (!client->name)
		goto err_free_client;

	down_write(&dev->lock);
	client->display_serial = ion_get_client_serial(&dev->clients, name);
	client->display_name = kasprintf(
		GFP_KERNEL, "%s-%d", name, client->display_serial);
	if (!client->display_name) {
		up_write(&dev->lock);
		goto err_free_client_name;
	}
	p = &dev->clients.rb_node;
	while (*p) {
		parent = *p;
		entry = rb_entry(parent, struct ion_client, node);

		if (client < entry)
			p = &(*p)->rb_left;
		else if (client > entry)
			p = &(*p)->rb_right;
	}
	rb_link_node(&client->node, parent, p);
	rb_insert_color(&client->node, &dev->clients);

	client->debug_root = debugfs_create_file(client->display_name, 0664,
						dev->clients_debug_root,
						client, &debug_client_fops);
	if (!client->debug_root) {
		char buf[256], *path;

		path = dentry_path(dev->clients_debug_root, buf, 256);
		pr_err("Failed to create client debugfs at %s/%s\n",
			path, client->display_name);
	}

	up_write(&dev->lock);

	return client;

err_free_client_name:
	kfree(client->name);
err_free_client:
	kfree(client);
err_put_task_struct:
	if (task)
		put_task_struct(current->group_leader);
	return ERR_PTR(-ENOMEM);
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.