struct ion_handle *ion_alloc(struct ion_client *client, size_t len,
			     size_t align, unsigned int heap_id_mask,
			     unsigned int flags)
{
	struct ion_handle *handle;
	struct ion_device *dev = client->dev;
	struct ion_buffer *buffer = NULL;
	struct ion_heap *heap;
	int ret;

	pr_debug("%s: len %zu align %zu heap_id_mask %u flags %x\n", __func__,
		 len, align, heap_id_mask, flags);
	/*
	 * traverse the list of heaps available in this system in priority
	 * order.  If the heap type is supported by the client, and matches the
	 * request of the caller allocate from it.  Repeat until allocate has
	 * succeeded or all heaps have been tried
	 */
	len = PAGE_ALIGN(len);

	if (!len)
		return ERR_PTR(-EINVAL);

	down_read(&dev->lock);
	plist_for_each_entry(heap, &dev->heaps, node) {
		/* if the caller didn't specify this heap id */
		if (!((1 << heap->id) & heap_id_mask))
			continue;
		buffer = ion_buffer_create(heap, dev, len, align, flags);
		if (!IS_ERR(buffer))
			break;
	}
	up_read(&dev->lock);

	if (buffer == NULL)
		return ERR_PTR(-ENODEV);

	if (IS_ERR(buffer))
		return ERR_CAST(buffer);

	handle = ion_handle_create(client, buffer);

	/*
	 * ion_buffer_create will create a buffer with a ref_cnt of 1,
	 * and ion_handle_create will take a second reference, drop one here
	 */
	ion_buffer_put(buffer);

	if (IS_ERR(handle))
		return handle;

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

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.