static void tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
		u8 type, u8 code, int offset, __be32 info)
{
	const struct ipv6hdr *hdr = (const struct ipv6hdr *)skb->data;
	const struct tcphdr *th = (struct tcphdr *)(skb->data+offset);
	struct net *net = dev_net(skb->dev);
	struct request_sock *fastopen;
	struct ipv6_pinfo *np;
	struct tcp_sock *tp;
	__u32 seq, snd_una;
	struct sock *sk;
	bool fatal;
	int err;

	sk = __inet6_lookup_established(net, &tcp_hashinfo,
					&hdr->daddr, th->dest,
					&hdr->saddr, ntohs(th->source),
					skb->dev->ifindex);

	if (!sk) {
		__ICMP6_INC_STATS(net, __in6_dev_get(skb->dev),
				  ICMP6_MIB_INERRORS);
		return;
	}

	if (sk->sk_state == TCP_TIME_WAIT) {
		inet_twsk_put(inet_twsk(sk));
		return;
	}
	seq = ntohl(th->seq);
	fatal = icmpv6_err_convert(type, code, &err);
	if (sk->sk_state == TCP_NEW_SYN_RECV)
		return tcp_req_err(sk, seq, fatal);

	bh_lock_sock(sk);
	if (sock_owned_by_user(sk) && type != ICMPV6_PKT_TOOBIG)
		__NET_INC_STATS(net, LINUX_MIB_LOCKDROPPEDICMPS);

	if (sk->sk_state == TCP_CLOSE)
		goto out;

	if (ipv6_hdr(skb)->hop_limit < inet6_sk(sk)->min_hopcount) {
		__NET_INC_STATS(net, LINUX_MIB_TCPMINTTLDROP);
		goto out;
	}

	tp = tcp_sk(sk);
	/* XXX (TFO) - tp->snd_una should be ISN (tcp_create_openreq_child() */
	fastopen = tp->fastopen_rsk;
	snd_una = fastopen ? tcp_rsk(fastopen)->snt_isn : tp->snd_una;
	if (sk->sk_state != TCP_LISTEN &&
	    !between(seq, snd_una, tp->snd_nxt)) {
		__NET_INC_STATS(net, LINUX_MIB_OUTOFWINDOWICMPS);
		goto out;
	}

	np = inet6_sk(sk);

	if (type == NDISC_REDIRECT) {
		if (!sock_owned_by_user(sk)) {
			struct dst_entry *dst = __sk_dst_check(sk, np->dst_cookie);

			if (dst)
				dst->ops->redirect(dst, sk, skb);
		}
		goto out;
	}

	if (type == ICMPV6_PKT_TOOBIG) {
		/* We are not interested in TCP_LISTEN and open_requests
		 * (SYN-ACKs send out by Linux are always <576bytes so
		 * they should go through unfragmented).
		 */
		if (sk->sk_state == TCP_LISTEN)
			goto out;

		if (!ip6_sk_accept_pmtu(sk))
			goto out;

		tp->mtu_info = ntohl(info);
		if (!sock_owned_by_user(sk))
			tcp_v6_mtu_reduced(sk);
		else if (!test_and_set_bit(TCP_MTU_REDUCED_DEFERRED,
					   &sk->sk_tsq_flags))
			sock_hold(sk);
		goto out;
	}


	/* Might be for an request_sock */
	switch (sk->sk_state) {
	case TCP_SYN_SENT:
	case TCP_SYN_RECV:
		/* Only in fast or simultaneous open. If a fast open socket is
		 * is already accepted it is treated as a connected one below.
		 */
		if (fastopen && !fastopen->sk)
			break;

		if (!sock_owned_by_user(sk)) {
			sk->sk_err = err;
			sk->sk_error_report(sk);		/* Wake people up to see the error (see connect in sock.c) */

			tcp_done(sk);
		} else
			sk->sk_err_soft = err;
		goto out;
	}

	if (!sock_owned_by_user(sk) && np->recverr) {
		sk->sk_err = err;
		sk->sk_error_report(sk);
	} else
		sk->sk_err_soft = err;

out:
	bh_unlock_sock(sk);
	sock_put(sk);
}

Unknown