static int blk_complete_sgv4_hdr_rq(struct request *rq, struct sg_io_v4 *hdr,
				    struct bio *bio, struct bio *bidi_bio)
{
	int ret = 0;

	dprintk("rq %p bio %p 0x%x\n", rq, bio, rq->errors);
	/*
	 * fill in all the output members
	 */
	hdr->device_status = rq->errors & 0xff;
	hdr->transport_status = host_byte(rq->errors);
	hdr->driver_status = driver_byte(rq->errors);
	hdr->info = 0;
	if (hdr->device_status || hdr->transport_status || hdr->driver_status)
		hdr->info |= SG_INFO_CHECK;
	hdr->response_len = 0;

	if (rq->sense_len && hdr->response) {
		int len = min_t(unsigned int, hdr->max_response_len,
					rq->sense_len);

		ret = copy_to_user((void __user *)(unsigned long)hdr->response,
				   rq->sense, len);
		if (!ret)
			hdr->response_len = len;
		else
			ret = -EFAULT;
	}

	if (rq->next_rq) {
		hdr->dout_resid = rq->resid_len;
		hdr->din_resid = rq->next_rq->resid_len;
		blk_rq_unmap_user(bidi_bio);
		blk_put_request(rq->next_rq);
	} else if (rq_data_dir(rq) == READ)
		hdr->din_resid = rq->resid_len;
	else
		hdr->dout_resid = rq->resid_len;

	/*
	 * If the request generated a negative error number, return it
	 * (providing we aren't already returning an error); if it's
	 * just a protocol response (i.e. non negative), that gets
	 * processed above.
	 */
	if (!ret && rq->errors < 0)
		ret = rq->errors;

	blk_rq_unmap_user(bio);
	if (rq->cmd != rq->__cmd)
		kfree(rq->cmd);
	blk_put_request(rq);

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.