void *ion_map_kernel(struct ion_client *client, struct ion_handle *handle)
{
	struct ion_buffer *buffer;
	void *vaddr;

	mutex_lock(&client->lock);
	if (!ion_handle_validate(client, handle)) {
		pr_err("%s: invalid handle passed to map_kernel.\n",
		       __func__);
		mutex_unlock(&client->lock);
		return ERR_PTR(-EINVAL);
	}

	buffer = handle->buffer;

	if (!handle->buffer->heap->ops->map_kernel) {
		pr_err("%s: map_kernel is not implemented by this heap.\n",
		       __func__);
		mutex_unlock(&client->lock);
		return ERR_PTR(-ENODEV);
	}

	mutex_lock(&buffer->lock);
	vaddr = ion_handle_kmap_get(handle);
	mutex_unlock(&buffer->lock);
	mutex_unlock(&client->lock);
	return vaddr;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.