blk_qc_t generic_make_request(struct bio *bio)
{
	/*
	 * bio_list_on_stack[0] contains bios submitted by the current
	 * make_request_fn.
	 * bio_list_on_stack[1] contains bios that were submitted before
	 * the current make_request_fn, but that haven't been processed
	 * yet.
	 */
	struct bio_list bio_list_on_stack[2];
	blk_mq_req_flags_t flags = 0;
	struct request_queue *q = bio->bi_disk->queue;
	blk_qc_t ret = BLK_QC_T_NONE;

	if (bio->bi_opf & REQ_NOWAIT)
		flags = BLK_MQ_REQ_NOWAIT;
	if (bio_flagged(bio, BIO_QUEUE_ENTERED))
		blk_queue_enter_live(q);
	else if (blk_queue_enter(q, flags) < 0) {
		if (!blk_queue_dying(q) && (bio->bi_opf & REQ_NOWAIT))
			bio_wouldblock_error(bio);
		else
			bio_io_error(bio);
		return ret;
	}

	if (!generic_make_request_checks(bio))
		goto out;

	/*
	 * We only want one ->make_request_fn to be active at a time, else
	 * stack usage with stacked devices could be a problem.  So use
	 * current->bio_list to keep a list of requests submited by a
	 * make_request_fn function.  current->bio_list is also used as a
	 * flag to say if generic_make_request is currently active in this
	 * task or not.  If it is NULL, then no make_request is active.  If
	 * it is non-NULL, then a make_request is active, and new requests
	 * should be added at the tail
	 */
	if (current->bio_list) {
		bio_list_add(&current->bio_list[0], bio);
		goto out;
	}

	/* following loop may be a bit non-obvious, and so deserves some
	 * explanation.
	 * Before entering the loop, bio->bi_next is NULL (as all callers
	 * ensure that) so we have a list with a single bio.
	 * We pretend that we have just taken it off a longer list, so
	 * we assign bio_list to a pointer to the bio_list_on_stack,
	 * thus initialising the bio_list of new bios to be
	 * added.  ->make_request() may indeed add some more bios
	 * through a recursive call to generic_make_request.  If it
	 * did, we find a non-NULL value in bio_list and re-enter the loop
	 * from the top.  In this case we really did just take the bio
	 * of the top of the list (no pretending) and so remove it from
	 * bio_list, and call into ->make_request() again.
	 */
	BUG_ON(bio->bi_next);
	bio_list_init(&bio_list_on_stack[0]);
	current->bio_list = bio_list_on_stack;
	do {
		bool enter_succeeded = true;

		if (unlikely(q != bio->bi_disk->queue)) {
			if (q)
				blk_queue_exit(q);
			q = bio->bi_disk->queue;
			flags = 0;
			if (bio->bi_opf & REQ_NOWAIT)
				flags = BLK_MQ_REQ_NOWAIT;
			if (blk_queue_enter(q, flags) < 0) {
				enter_succeeded = false;
				q = NULL;
			}
		}

		if (enter_succeeded) {
			struct bio_list lower, same;

			/* Create a fresh bio_list for all subordinate requests */
			bio_list_on_stack[1] = bio_list_on_stack[0];
			bio_list_init(&bio_list_on_stack[0]);
			ret = q->make_request_fn(q, bio);

			/* sort new bios into those for a lower level
			 * and those for the same level
			 */
			bio_list_init(&lower);
			bio_list_init(&same);
			while ((bio = bio_list_pop(&bio_list_on_stack[0])) != NULL)
				if (q == bio->bi_disk->queue)
					bio_list_add(&same, bio);
				else
					bio_list_add(&lower, bio);
			/* now assemble so we handle the lowest level first */
			bio_list_merge(&bio_list_on_stack[0], &lower);
			bio_list_merge(&bio_list_on_stack[0], &same);
			bio_list_merge(&bio_list_on_stack[0], &bio_list_on_stack[1]);
		} else {
			if (unlikely(!blk_queue_dying(q) &&
					(bio->bi_opf & REQ_NOWAIT)))
				bio_wouldblock_error(bio);
			else
				bio_io_error(bio);
		}
		bio = bio_list_pop(&bio_list_on_stack[0]);
	} while (bio);
	current->bio_list = NULL; /* deactivate */

out:
	if (q)
		blk_queue_exit(q);
	return ret;
}

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.