static int blk_cloned_rq_check_limits(struct request_queue *q,
				      struct request *rq)
{
	if (blk_rq_sectors(rq) > blk_queue_get_max_sectors(q, req_op(rq))) {
		printk(KERN_ERR "%s: over max size limit.\n", __func__);
		return -EIO;
	}

	/*
	 * queue's settings related to segment counting like q->bounce_pfn
	 * may differ from that of other stacking queues.
	 * Recalculate it to check the request correctly on this queue's
	 * limitation.
	 */
	blk_recalc_rq_segments(rq);
	if (rq->nr_phys_segments > queue_max_segments(q)) {
		printk(KERN_ERR "%s: over max segments limit.\n", __func__);
		return -EIO;
	}

	return 0;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.