__bsg_read(char __user *buf, size_t count, struct bsg_device *bd,
	   const struct iovec *iov, ssize_t *bytes_read)
{
	struct bsg_command *bc;
	int nr_commands, ret;

	if (count % sizeof(struct sg_io_v4))
		return -EINVAL;

	ret = 0;
	nr_commands = count / sizeof(struct sg_io_v4);
	while (nr_commands) {
		bc = bsg_get_done_cmd(bd);
		if (IS_ERR(bc)) {
			ret = PTR_ERR(bc);
			break;
		}

		/*
		 * this is the only case where we need to copy data back
		 * after completing the request. so do that here,
		 * bsg_complete_work() cannot do that for us
		 */
		ret = blk_complete_sgv4_hdr_rq(bc->rq, &bc->hdr, bc->bio,
					       bc->bidi_bio);

		if (copy_to_user(buf, &bc->hdr, sizeof(bc->hdr)))
			ret = -EFAULT;

		bsg_free_command(bc);

		if (ret)
			break;

		buf += sizeof(struct sg_io_v4);
		*bytes_read += sizeof(struct sg_io_v4);
		nr_commands--;
	}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.