struct sock *inet_csk_accept(struct sock *sk, int flags, int *err, bool kern)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct request_sock_queue *queue = &icsk->icsk_accept_queue;
	struct request_sock *req;
	struct sock *newsk;
	int error;

	lock_sock(sk);

	/* We need to make sure that this socket is listening,
	 * and that it has something pending.
	 */
	error = -EINVAL;
	if (sk->sk_state != TCP_LISTEN)
		goto out_err;

	/* Find already established connection */
	if (reqsk_queue_empty(queue)) {
		long timeo = sock_rcvtimeo(sk, flags & O_NONBLOCK);

		/* If this is a non blocking socket don't sleep */
		error = -EAGAIN;
		if (!timeo)
			goto out_err;

		error = inet_csk_wait_for_connect(sk, timeo);
		if (error)
			goto out_err;
	}
	req = reqsk_queue_remove(queue, sk);
	newsk = req->sk;

	if (sk->sk_protocol == IPPROTO_TCP &&
	    tcp_rsk(req)->tfo_listener) {
		spin_lock_bh(&queue->fastopenq.lock);
		if (tcp_rsk(req)->tfo_listener) {
			/* We are still waiting for the final ACK from 3WHS
			 * so can't free req now. Instead, we set req->sk to
			 * NULL to signify that the child socket is taken
			 * so reqsk_fastopen_remove() will free the req
			 * when 3WHS finishes (or is aborted).
			 */
			req->sk = NULL;
			req = NULL;
		}
		spin_unlock_bh(&queue->fastopenq.lock);
	}
out:
	release_sock(sk);
	if (req)
		reqsk_put(req);
	return newsk;
out_err:
	newsk = NULL;
	req = NULL;
	*err = error;
	goto out;
}

The product calls free() twice on the same memory address, potentially leading to modification of unexpected memory locations.