struct ion_device *ion_device_create(long (*custom_ioctl)
				     (struct ion_client *client,
				      unsigned int cmd,
				      unsigned long arg))
{
	struct ion_device *idev;
	int ret;

	idev = kzalloc(sizeof(struct ion_device), GFP_KERNEL);
	if (!idev)
		return ERR_PTR(-ENOMEM);

	idev->dev.minor = MISC_DYNAMIC_MINOR;
	idev->dev.name = "ion";
	idev->dev.fops = &ion_fops;
	idev->dev.parent = NULL;
	ret = misc_register(&idev->dev);
	if (ret) {
		pr_err("ion: failed to register misc device.\n");
		kfree(idev);
		return ERR_PTR(ret);
	}

	idev->debug_root = debugfs_create_dir("ion", NULL);
	if (!idev->debug_root) {
		pr_err("ion: failed to create debugfs root directory.\n");
		goto debugfs_done;
	}
	idev->heaps_debug_root = debugfs_create_dir("heaps", idev->debug_root);
	if (!idev->heaps_debug_root) {
		pr_err("ion: failed to create debugfs heaps directory.\n");
		goto debugfs_done;
	}
	idev->clients_debug_root = debugfs_create_dir("clients",
						idev->debug_root);
	if (!idev->clients_debug_root)
		pr_err("ion: failed to create debugfs clients directory.\n");

debugfs_done:

	idev->custom_ioctl = custom_ioctl;
	idev->buffers = RB_ROOT;
	mutex_init(&idev->buffer_lock);
	init_rwsem(&idev->lock);
	plist_head_init(&idev->heaps);
	idev->clients = RB_ROOT;
	ion_root_client = &idev->clients;
	mutex_init(&debugfs_mutex);
	return idev;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.