void ion_free(struct ion_client *client, struct ion_handle *handle)
static void ion_free_nolock(struct ion_client *client, struct ion_handle *handle)
 {
 	bool valid_handle;
 
 	BUG_ON(client != handle->client);
 
 	valid_handle = ion_handle_validate(client, handle);
 
 	if (!valid_handle) {
 		WARN(1, "%s: invalid handle passed to free.\n", __func__);
 		return;
 	}
	ion_handle_put_nolock(handle);
}

void ion_free(struct ion_client *client, struct ion_handle *handle)
{
	BUG_ON(client != handle->client);

	mutex_lock(&client->lock);
	ion_free_nolock(client, handle);
 	mutex_unlock(&client->lock);
 }

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.