struct sock *inet_csk_reqsk_queue_add(struct sock *sk,
				      struct request_sock *req,
				      struct sock *child)
{
	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;

	spin_lock(&queue->rskq_lock);
	if (unlikely(sk->sk_state != TCP_LISTEN)) {
		inet_child_forget(sk, req, child);
		child = NULL;
	} else {
		req->sk = child;
		req->dl_next = NULL;
		if (queue->rskq_accept_head == NULL)
			queue->rskq_accept_head = req;
		else
			queue->rskq_accept_tail->dl_next = req;
		queue->rskq_accept_tail = req;
		sk_acceptq_added(sk);
	}
	spin_unlock(&queue->rskq_lock);
	return child;
}

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