struct ion_handle *ion_import_dma_buf(struct ion_client *client,
				      struct dma_buf *dmabuf)
{
	struct ion_buffer *buffer;
	struct ion_handle *handle;
	int ret;

	/* if this memory came from ion */

	if (dmabuf->ops != &dma_buf_ops) {
		pr_err("%s: can not import dmabuf from another exporter\n",
		       __func__);
		return ERR_PTR(-EINVAL);
	}
	buffer = dmabuf->priv;

	mutex_lock(&client->lock);
	/* if a handle exists for this buffer just take a reference to it */
	handle = ion_handle_lookup(client, buffer);
	if (!IS_ERR(handle)) {
		ion_handle_get(handle);
		mutex_unlock(&client->lock);
		goto end;
	}

	handle = ion_handle_create(client, buffer);
	if (IS_ERR(handle)) {
		mutex_unlock(&client->lock);
		goto end;
	}

	ret = ion_handle_add(client, handle);
	mutex_unlock(&client->lock);
	if (ret) {
		ion_handle_put(handle);
		handle = ERR_PTR(ret);
	}

end:
	return handle;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.