static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
			  int addr_len)
{
	struct sockaddr_in6 *usin = (struct sockaddr_in6 *) uaddr;
	struct inet_sock *inet = inet_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct ipv6_pinfo *np = inet6_sk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	struct in6_addr *saddr = NULL, *final_p, final;
	struct ipv6_txoptions *opt;
	struct flowi6 fl6;
	struct dst_entry *dst;
	int addr_type;
	int err;
	struct inet_timewait_death_row *tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row;

	if (addr_len < SIN6_LEN_RFC2133)
		return -EINVAL;

	if (usin->sin6_family != AF_INET6)
		return -EAFNOSUPPORT;

	memset(&fl6, 0, sizeof(fl6));

	if (np->sndflow) {
		fl6.flowlabel = usin->sin6_flowinfo&IPV6_FLOWINFO_MASK;
		IP6_ECN_flow_init(fl6.flowlabel);
		if (fl6.flowlabel&IPV6_FLOWLABEL_MASK) {
			struct ip6_flowlabel *flowlabel;
			flowlabel = fl6_sock_lookup(sk, fl6.flowlabel);
			if (!flowlabel)
				return -EINVAL;
			fl6_sock_release(flowlabel);
		}
	}

	/*
	 *	connect() to INADDR_ANY means loopback (BSD'ism).
	 */

	if (ipv6_addr_any(&usin->sin6_addr)) {
		if (ipv6_addr_v4mapped(&sk->sk_v6_rcv_saddr))
			ipv6_addr_set_v4mapped(htonl(INADDR_LOOPBACK),
					       &usin->sin6_addr);
		else
			usin->sin6_addr = in6addr_loopback;
	}

	addr_type = ipv6_addr_type(&usin->sin6_addr);

	if (addr_type & IPV6_ADDR_MULTICAST)
		return -ENETUNREACH;

	if (addr_type&IPV6_ADDR_LINKLOCAL) {
		if (addr_len >= sizeof(struct sockaddr_in6) &&
		    usin->sin6_scope_id) {
			/* If interface is set while binding, indices
			 * must coincide.
			 */
			if (sk->sk_bound_dev_if &&
			    sk->sk_bound_dev_if != usin->sin6_scope_id)
				return -EINVAL;

			sk->sk_bound_dev_if = usin->sin6_scope_id;
		}

		/* Connect to link-local address requires an interface */
		if (!sk->sk_bound_dev_if)
			return -EINVAL;
	}

	if (tp->rx_opt.ts_recent_stamp &&
	    !ipv6_addr_equal(&sk->sk_v6_daddr, &usin->sin6_addr)) {
		tp->rx_opt.ts_recent = 0;
		tp->rx_opt.ts_recent_stamp = 0;
		tp->write_seq = 0;
	}

	sk->sk_v6_daddr = usin->sin6_addr;
	np->flow_label = fl6.flowlabel;

	/*
	 *	TCP over IPv4
	 */

	if (addr_type & IPV6_ADDR_MAPPED) {
		u32 exthdrlen = icsk->icsk_ext_hdr_len;
		struct sockaddr_in sin;

		SOCK_DEBUG(sk, "connect: ipv4 mapped\n");

		if (__ipv6_only_sock(sk))
			return -ENETUNREACH;

		sin.sin_family = AF_INET;
		sin.sin_port = usin->sin6_port;
		sin.sin_addr.s_addr = usin->sin6_addr.s6_addr32[3];

		icsk->icsk_af_ops = &ipv6_mapped;
		sk->sk_backlog_rcv = tcp_v4_do_rcv;
#ifdef CONFIG_TCP_MD5SIG
		tp->af_specific = &tcp_sock_ipv6_mapped_specific;
#endif

		err = tcp_v4_connect(sk, (struct sockaddr *)&sin, sizeof(sin));

		if (err) {
			icsk->icsk_ext_hdr_len = exthdrlen;
			icsk->icsk_af_ops = &ipv6_specific;
			sk->sk_backlog_rcv = tcp_v6_do_rcv;
#ifdef CONFIG_TCP_MD5SIG
			tp->af_specific = &tcp_sock_ipv6_specific;
#endif
			goto failure;
		}
		np->saddr = sk->sk_v6_rcv_saddr;

		return err;
	}

	if (!ipv6_addr_any(&sk->sk_v6_rcv_saddr))
		saddr = &sk->sk_v6_rcv_saddr;

	fl6.flowi6_proto = IPPROTO_TCP;
	fl6.daddr = sk->sk_v6_daddr;
	fl6.saddr = saddr ? *saddr : np->saddr;
	fl6.flowi6_oif = sk->sk_bound_dev_if;
	fl6.flowi6_mark = sk->sk_mark;
	fl6.fl6_dport = usin->sin6_port;
	fl6.fl6_sport = inet->inet_sport;
	fl6.flowi6_uid = sk->sk_uid;

	opt = rcu_dereference_protected(np->opt, lockdep_sock_is_held(sk));
	final_p = fl6_update_dst(&fl6, opt, &final);

	security_sk_classify_flow(sk, flowi6_to_flowi(&fl6));

	dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
	if (IS_ERR(dst)) {
		err = PTR_ERR(dst);
		goto failure;
	}

	if (!saddr) {
		saddr = &fl6.saddr;
		sk->sk_v6_rcv_saddr = *saddr;
	}

	/* set the source address */
	np->saddr = *saddr;
	inet->inet_rcv_saddr = LOOPBACK4_IPV6;

	sk->sk_gso_type = SKB_GSO_TCPV6;
	ip6_dst_store(sk, dst, NULL, NULL);

	icsk->icsk_ext_hdr_len = 0;
	if (opt)
		icsk->icsk_ext_hdr_len = opt->opt_flen +
					 opt->opt_nflen;

	tp->rx_opt.mss_clamp = IPV6_MIN_MTU - sizeof(struct tcphdr) - sizeof(struct ipv6hdr);

	inet->inet_dport = usin->sin6_port;

	tcp_set_state(sk, TCP_SYN_SENT);
	err = inet6_hash_connect(tcp_death_row, sk);
	if (err)
		goto late_failure;

	sk_set_txhash(sk);

	if (likely(!tp->repair)) {
		if (!tp->write_seq)
			tp->write_seq = secure_tcpv6_seq(np->saddr.s6_addr32,
							 sk->sk_v6_daddr.s6_addr32,
							 inet->inet_sport,
							 inet->inet_dport);
		tp->tsoffset = secure_tcpv6_ts_off(np->saddr.s6_addr32,
						   sk->sk_v6_daddr.s6_addr32);
	}

	if (tcp_fastopen_defer_connect(sk, &err))
		return err;
	if (err)
		goto late_failure;

	err = tcp_connect(sk);
	if (err)
		goto late_failure;

	return 0;

late_failure:
	tcp_set_state(sk, TCP_CLOSE);
failure:
	inet->inet_dport = 0;
	sk->sk_route_caps = 0;
	return err;
}

Unknown