l2tp: introduce L2TPv3 IP encapsulation support for IPv6

L2TPv3 defines an IP encapsulation packet format where data is carried
directly over IP (no UDP). The kernel already has support for L2TP IP
encapsulation over IPv4 (l2tp_ip). This patch introduces support for
L2TP IP encapsulation over IPv6.

The implementation is derived from ipv6/raw and ipv4/l2tp_ip.

Signed-off-by: Chris Elston <[e-mail]>
Signed-off-by: James Chapman <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/l2tp.h

···
 #include <linux/socket.h>
 #ifdef __KERNEL__
 #include <linux/in.h>
+#include <linux/in6.h>
 #else
 #include <netinet/in.h>
 #endif
···
 			      sizeof(__kernel_sa_family_t) -
 			      sizeof(__be16) - sizeof(struct in_addr) -
 			      sizeof(__u32)];
+};
+
+/**
+ * struct sockaddr_l2tpip6 - the sockaddr structure for L2TP-over-IPv6 sockets
+ * @l2tp_family:  address family number AF_L2TPIP.
+ * @l2tp_addr:    protocol specific address information
+ * @l2tp_conn_id: connection id of tunnel
+ */
+struct sockaddr_l2tpip6 {
+	/* The first fields must match struct sockaddr_in6 */
+	__kernel_sa_family_t l2tp_family; /* AF_INET6 */
+	__be16		l2tp_unused;	/* INET port number (unused) */
+	__be32		l2tp_flowinfo;	/* IPv6 flow information */
+	struct in6_addr	l2tp_addr;	/* IPv6 address */
+	__u32		l2tp_scope_id;	/* scope id (new in RFC2553) */
+	__u32		l2tp_conn_id;	/* Connection ID of tunnel */
 };
 
 /*****************************************************************************

net/l2tp/Makefile

···
 obj-$(subst y,$(CONFIG_L2TP),$(CONFIG_L2TP_V3)) += l2tp_netlink.o
 obj-$(subst y,$(CONFIG_L2TP),$(CONFIG_L2TP_ETH)) += l2tp_eth.o
 obj-$(subst y,$(CONFIG_L2TP),$(CONFIG_L2TP_DEBUGFS)) += l2tp_debugfs.o
+ifneq ($(CONFIG_IPV6),)
+obj-$(subst y,$(CONFIG_L2TP),$(CONFIG_L2TP_IP)) += l2tp_ip6.o
+endif

net/l2tp/l2tp_ip6.c

···
+/*
+ * L2TPv3 IP encapsulation support for IPv6
+ *
+ * Copyright (c) 2012 Katalix Systems Ltd
+ *
+ *	This program is free software; you can redistribute it and/or
+ *	modify it under the terms of the GNU General Public License
+ *	as published by the Free Software Foundation; either version
+ *	2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/icmp.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/random.h>
+#include <linux/socket.h>
+#include <linux/l2tp.h>
+#include <linux/in.h>
+#include <linux/in6.h>
+#include <net/sock.h>
+#include <net/ip.h>
+#include <net/icmp.h>
+#include <net/udp.h>
+#include <net/inet_common.h>
+#include <net/inet_hashtables.h>
+#include <net/tcp_states.h>
+#include <net/protocol.h>
+#include <net/xfrm.h>
+
+#include <net/transp_v6.h>
+#include <net/addrconf.h>
+#include <net/ip6_route.h>
+
+#include "l2tp_core.h"
+
+struct l2tp_ip6_sock {
+	/* inet_sock has to be the first member of l2tp_ip6_sock */
+	struct inet_sock	inet;
+
+	u32			conn_id;
+	u32			peer_conn_id;
+
+	/* ipv6_pinfo has to be the last member of l2tp_ip6_sock, see
+	   inet6_sk_generic */
+	struct ipv6_pinfo	inet6;
+};
+
+static DEFINE_RWLOCK(l2tp_ip6_lock);
+static struct hlist_head l2tp_ip6_table;
+static struct hlist_head l2tp_ip6_bind_table;
+
+static inline struct l2tp_ip6_sock *l2tp_ip6_sk(const struct sock *sk)
+{
+	return (struct l2tp_ip6_sock *)sk;
+}
+
+static struct sock *__l2tp_ip6_bind_lookup(struct net *net,
+					   struct in6_addr *laddr,
+					   int dif, u32 tunnel_id)
+{
+	struct hlist_node *node;
+	struct sock *sk;
+
+	sk_for_each_bound(sk, node, &l2tp_ip6_bind_table) {
+		struct in6_addr *addr = inet6_rcv_saddr(sk);
+		struct l2tp_ip6_sock *l2tp = l2tp_ip6_sk(sk);
+
+		if (l2tp == NULL)
+			continue;
+
+		if ((l2tp->conn_id == tunnel_id) &&
+		    net_eq(sock_net(sk), net) &&
+		    !(addr && ipv6_addr_equal(addr, laddr)) &&
+		    !(sk->sk_bound_dev_if && sk->sk_bound_dev_if != dif))
+			goto found;
+	}
+
+	sk = NULL;
+found:
+	return sk;
+}
+
+static inline struct sock *l2tp_ip6_bind_lookup(struct net *net,
+						struct in6_addr *laddr,
+						int dif, u32 tunnel_id)
+{
+	struct sock *sk = __l2tp_ip6_bind_lookup(net, laddr, dif, tunnel_id);
+	if (sk)
+		sock_hold(sk);
+
+	return sk;
+}
+
+/* When processing receive frames, there are two cases to
+ * consider. Data frames consist of a non-zero session-id and an
+ * optional cookie. Control frames consist of a regular L2TP header
+ * preceded by 32-bits of zeros.
+ *
+ * L2TPv3 Session Header Over IP
+ *
+ *  0                   1                   2                   3
+ *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |                           Session ID                          |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |               Cookie (optional, maximum 64 bits)...
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *                                                                 |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ * L2TPv3 Control Message Header Over IP
+ *
+ *  0                   1                   2                   3
+ *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |                      (32 bits of zeros)                       |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |T|L|x|x|S|x|x|x|x|x|x|x|  Ver  |             Length            |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |                     Control Connection ID                     |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |               Ns              |               Nr              |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ * All control frames are passed to userspace.
+ */
+static int l2tp_ip6_recv(struct sk_buff *skb)
+{
+	struct sock *sk;
+	u32 session_id;
+	u32 tunnel_id;
+	unsigned char *ptr, *optr;
+	struct l2tp_session *session;
+	struct l2tp_tunnel *tunnel = NULL;
+	int length;
+	int offset;
+
+	/* Point to L2TP header */
+	optr = ptr = skb->data;
+
+	if (!pskb_may_pull(skb, 4))
+		goto discard;
+
+	session_id = ntohl(*((__be32 *) ptr));
+	ptr += 4;
+
+	/* RFC3931: L2TP/IP packets have the first 4 bytes containing
+	 * the session_id. If it is 0, the packet is a L2TP control
+	 * frame and the session_id value can be discarded.
+	 */
+	if (session_id == 0) {
+		__skb_pull(skb, 4);
+		goto pass_up;
+	}
+
+	/* Ok, this is a data packet. Lookup the session. */
+	session = l2tp_session_find(&init_net, NULL, session_id);
+	if (session == NULL)
+		goto discard;
+
+	tunnel = session->tunnel;
+	if (tunnel == NULL)
+		goto discard;
+
+	/* Trace packet contents, if enabled */
+	if (tunnel->debug & L2TP_MSG_DATA) {
+		length = min(32u, skb->len);
+		if (!pskb_may_pull(skb, length))
+			goto discard;
+
+		printk(KERN_DEBUG "%s: ip recv: ", tunnel->name);
+
+		offset = 0;
+		do {
+			printk(" %02X", ptr[offset]);
+		} while (++offset < length);
+
+		printk("\n");
+	}
+
+	l2tp_recv_common(session, skb, ptr, optr, 0, skb->len,
+			 tunnel->recv_payload_hook);
+	return 0;
+
+pass_up:
+	/* Get the tunnel_id from the L2TP header */
+	if (!pskb_may_pull(skb, 12))
+		goto discard;
+
+	if ((skb->data[0] & 0xc0) != 0xc0)
+		goto discard;
+
+	tunnel_id = ntohl(*(__be32 *) &skb->data[4]);
+	tunnel = l2tp_tunnel_find(&init_net, tunnel_id);
+	if (tunnel != NULL)
+		sk = tunnel->sock;
+	else {
+		struct ipv6hdr *iph = ipv6_hdr(skb);
+
+		read_lock_bh(&l2tp_ip6_lock);
+		sk = __l2tp_ip6_bind_lookup(&init_net, &iph->daddr,
+					    0, tunnel_id);
+		read_unlock_bh(&l2tp_ip6_lock);
+	}
+
+	if (sk == NULL)
+		goto discard;
+
+	sock_hold(sk);
+
+	if (!xfrm6_policy_check(sk, XFRM_POLICY_IN, skb))
+		goto discard_put;
+
+	nf_reset(skb);
+
+	return sk_receive_skb(sk, skb, 1);
+
+discard_put:
+	sock_put(sk);
+
+discard:
+	kfree_skb(skb);
+	return 0;
+}
+
+static int l2tp_ip6_open(struct sock *sk)
+{
+	/* Prevent autobind. We don't have ports. */
+	inet_sk(sk)->inet_num = IPPROTO_L2TP;
+
+	write_lock_bh(&l2tp_ip6_lock);
+	sk_add_node(sk, &l2tp_ip6_table);
+	write_unlock_bh(&l2tp_ip6_lock);
+
+	return 0;
+}
+
+static void l2tp_ip6_close(struct sock *sk, long timeout)
+{
+	write_lock_bh(&l2tp_ip6_lock);
+	hlist_del_init(&sk->sk_bind_node);
+	sk_del_node_init(sk);
+	write_unlock_bh(&l2tp_ip6_lock);
+
+	sk_common_release(sk);
+}
+
+static void l2tp_ip6_destroy_sock(struct sock *sk)
+{
+	lock_sock(sk);
+	ip6_flush_pending_frames(sk);
+	release_sock(sk);
+
+	inet6_destroy_sock(sk);
+}
+
+static int l2tp_ip6_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
+{
+	struct inet_sock *inet = inet_sk(sk);
+	struct ipv6_pinfo *np = inet6_sk(sk);
+	struct sockaddr_l2tpip6 *addr = (struct sockaddr_l2tpip6 *) uaddr;
+	__be32 v4addr = 0;
+	int addr_type;
+	int err;
+
+	if (addr_len < sizeof(*addr))
+		return -EINVAL;
+
+	addr_type = ipv6_addr_type(&addr->l2tp_addr);
+
+	/* l2tp_ip6 sockets are IPv6 only */
+	if (addr_type == IPV6_ADDR_MAPPED)
+		return -EADDRNOTAVAIL;
+
+	/* L2TP is point-point, not multicast */
+	if (addr_type & IPV6_ADDR_MULTICAST)
+		return -EADDRNOTAVAIL;
+
+	err = -EADDRINUSE;
+	read_lock_bh(&l2tp_ip6_lock);
+	if (__l2tp_ip6_bind_lookup(&init_net, &addr->l2tp_addr,
+				   sk->sk_bound_dev_if, addr->l2tp_conn_id))
+		goto out_in_use;
+	read_unlock_bh(&l2tp_ip6_lock);
+
+	lock_sock(sk);
+
+	err = -EINVAL;
+	if (sk->sk_state != TCP_CLOSE)
+		goto out_unlock;
+
+	/* Check if the address belongs to the host. */
+	rcu_read_lock();
+	if (addr_type != IPV6_ADDR_ANY) {
+		struct net_device *dev = NULL;
+
+		if (addr_type & IPV6_ADDR_LINKLOCAL) {
+			if (addr_len >= sizeof(struct sockaddr_in6) &&
+			    addr->l2tp_scope_id) {
+				/* Override any existing binding, if another
+				 * one is supplied by user.
+				 */
+				sk->sk_bound_dev_if = addr->l2tp_scope_id;
+			}
+
+			/* Binding to link-local address requires an
+			   interface */
+			if (!sk->sk_bound_dev_if)
+				goto out_unlock_rcu;
+
+			err = -ENODEV;
+			dev = dev_get_by_index_rcu(sock_net(sk),
+						   sk->sk_bound_dev_if);
+			if (!dev)
+				goto out_unlock_rcu;
+		}
+
+		/* ipv4 addr of the socket is invalid.  Only the
+		 * unspecified and mapped address have a v4 equivalent.
+		 */
+		v4addr = LOOPBACK4_IPV6;
+		err = -EADDRNOTAVAIL;
+		if (!ipv6_chk_addr(sock_net(sk), &addr->l2tp_addr, dev, 0))
+			goto out_unlock_rcu;
+	}
+	rcu_read_unlock();
+
+	inet->inet_rcv_saddr = inet->inet_saddr = v4addr;
+	np->rcv_saddr = addr->l2tp_addr;
+	np->saddr = addr->l2tp_addr;
+
+	l2tp_ip6_sk(sk)->conn_id = addr->l2tp_conn_id;
+
+	write_lock_bh(&l2tp_ip6_lock);
+	sk_add_bind_node(sk, &l2tp_ip6_bind_table);
+	sk_del_node_init(sk);
+	write_unlock_bh(&l2tp_ip6_lock);
+
+	release_sock(sk);
+	return 0;
+
+out_unlock_rcu:
+	rcu_read_unlock();
+out_unlock:
+	release_sock(sk);
+	return err;
+
+out_in_use:
+	read_unlock_bh(&l2tp_ip6_lock);
+	return err;
+}
+
+static int l2tp_ip6_connect(struct sock *sk, struct sockaddr *uaddr,
+			    int addr_len)
+{
+	struct sockaddr_l2tpip6 *lsa = (struct sockaddr_l2tpip6 *) uaddr;
+	struct sockaddr_in6	*usin = (struct sockaddr_in6 *) uaddr;
+	struct in6_addr	*daddr;
+	int	addr_type;
+	int rc;
+
+	if (addr_len < sizeof(*lsa))
+		return -EINVAL;
+
+	addr_type = ipv6_addr_type(&usin->sin6_addr);
+	if (addr_type & IPV6_ADDR_MULTICAST)
+		return -EINVAL;
+
+	if (addr_type & IPV6_ADDR_MAPPED) {
+		daddr = &usin->sin6_addr;
+		if (ipv4_is_multicast(daddr->s6_addr32[3]))
+			return -EINVAL;
+	}
+
+	rc = ip6_datagram_connect(sk, uaddr, addr_len);
+
+	lock_sock(sk);
+
+	l2tp_ip6_sk(sk)->peer_conn_id = lsa->l2tp_conn_id;
+
+	write_lock_bh(&l2tp_ip6_lock);
+	hlist_del_init(&sk->sk_bind_node);
+	sk_add_bind_node(sk, &l2tp_ip6_bind_table);
+	write_unlock_bh(&l2tp_ip6_lock);
+
+	release_sock(sk);
+
+	return rc;
+}
+
+static int l2tp_ip6_getname(struct socket *sock, struct sockaddr *uaddr,
+			    int *uaddr_len, int peer)
+{
+	struct sockaddr_l2tpip6 *lsa = (struct sockaddr_l2tpip6 *)uaddr;
+	struct sock *sk = sock->sk;
+	struct ipv6_pinfo *np = inet6_sk(sk);
+	struct l2tp_ip6_sock *lsk = l2tp_ip6_sk(sk);
+
+	lsa->l2tp_family = AF_INET6;
+	lsa->l2tp_flowinfo = 0;
+	lsa->l2tp_scope_id = 0;
+	if (peer) {
+		if (!lsk->peer_conn_id)
+			return -ENOTCONN;
+		lsa->l2tp_conn_id = lsk->peer_conn_id;
+		lsa->l2tp_addr = np->daddr;
+		if (np->sndflow)
+			lsa->l2tp_flowinfo = np->flow_label;
+	} else {
+		if (ipv6_addr_any(&np->rcv_saddr))
+			lsa->l2tp_addr = np->saddr;
+		else
+			lsa->l2tp_addr = np->rcv_saddr;
+
+		lsa->l2tp_conn_id = lsk->conn_id;
+	}
+	if (ipv6_addr_type(&lsa->l2tp_addr) & IPV6_ADDR_LINKLOCAL)
+		lsa->l2tp_scope_id = sk->sk_bound_dev_if;
+	*uaddr_len = sizeof(*lsa);
+	return 0;
+}
+
+static int l2tp_ip6_backlog_recv(struct sock *sk, struct sk_buff *skb)
+{
+	int rc;
+
+	/* Charge it to the socket, dropping if the queue is full. */
+	rc = sock_queue_rcv_skb(sk, skb);
+	if (rc < 0)
+		goto drop;
+
+	return 0;
+
+drop:
+	IP_INC_STATS(&init_net, IPSTATS_MIB_INDISCARDS);
+	kfree_skb(skb);
+	return -1;
+}
+
+static int l2tp_ip6_push_pending_frames(struct sock *sk)
+{
+	struct sk_buff *skb;
+	__be32 *transhdr = NULL;
+	int err = 0;
+
+	skb = skb_peek(&sk->sk_write_queue);
+	if (skb == NULL)
+		goto out;
+
+	transhdr = (__be32 *)skb_transport_header(skb);
+	*transhdr = 0;
+
+	err = ip6_push_pending_frames(sk);
+
+out:
+	return err;
+}
+
+/* Userspace will call sendmsg() on the tunnel socket to send L2TP
+ * control frames.
+ */
+static int l2tp_ip6_sendmsg(struct kiocb *iocb, struct sock *sk,
+			    struct msghdr *msg, size_t len)
+{
+	struct ipv6_txoptions opt_space;
+	struct sockaddr_l2tpip6 *lsa =
+		(struct sockaddr_l2tpip6 *) msg->msg_name;
+	struct in6_addr *daddr, *final_p, final;
+	struct ipv6_pinfo *np = inet6_sk(sk);
+	struct ipv6_txoptions *opt = NULL;
+	struct ip6_flowlabel *flowlabel = NULL;
+	struct dst_entry *dst = NULL;
+	struct flowi6 fl6;
+	int addr_len = msg->msg_namelen;
+	int hlimit = -1;
+	int tclass = -1;
+	int dontfrag = -1;
+	int transhdrlen = 4; /* zero session-id */
+	int ulen = len + transhdrlen;
+	int err;
+
+	/* Rough check on arithmetic overflow,
+	   better check is made in ip6_append_data().
+	 */
+	if (len > INT_MAX)
+		return -EMSGSIZE;
+
+	/* Mirror BSD error message compatibility */
+	if (msg->msg_flags & MSG_OOB)
+		return -EOPNOTSUPP;
+
+	/*
+	 *	Get and verify the address.
+	 */
+	memset(&fl6, 0, sizeof(fl6));
+
+	fl6.flowi6_mark = sk->sk_mark;
+
+	if (lsa) {
+		if (addr_len < SIN6_LEN_RFC2133)
+			return -EINVAL;
+
+		if (lsa->l2tp_family && lsa->l2tp_family != AF_INET6)
+			return -EAFNOSUPPORT;
+
+		daddr = &lsa->l2tp_addr;
+		if (np->sndflow) {
+			fl6.flowlabel = lsa->l2tp_flowinfo & IPV6_FLOWINFO_MASK;
+			if (fl6.flowlabel&IPV6_FLOWLABEL_MASK) {
+				flowlabel = fl6_sock_lookup(sk, fl6.flowlabel);
+				if (flowlabel == NULL)
+					return -EINVAL;
+				daddr = &flowlabel->dst;
+			}
+		}
+
+		/*
+		 * Otherwise it will be difficult to maintain
+		 * sk->sk_dst_cache.
+		 */
+		if (sk->sk_state == TCP_ESTABLISHED &&
+		    ipv6_addr_equal(daddr, &np->daddr))
+			daddr = &np->daddr;
+
+		if (addr_len >= sizeof(struct sockaddr_in6) &&
+		    lsa->l2tp_scope_id &&
+		    ipv6_addr_type(daddr) & IPV6_ADDR_LINKLOCAL)
+			fl6.flowi6_oif = lsa->l2tp_scope_id;
+	} else {
+		if (sk->sk_state != TCP_ESTABLISHED)
+			return -EDESTADDRREQ;
+
+		daddr = &np->daddr;
+		fl6.flowlabel = np->flow_label;
+	}
+
+	if (fl6.flowi6_oif == 0)
+		fl6.flowi6_oif = sk->sk_bound_dev_if;
+
+	if (msg->msg_controllen) {
+		opt = &opt_space;
+		memset(opt, 0, sizeof(struct ipv6_txoptions));
+		opt->tot_len = sizeof(struct ipv6_txoptions);
+
+		err = datagram_send_ctl(sock_net(sk), sk, msg, &fl6, opt,
+					&hlimit, &tclass, &dontfrag);
+		if (err < 0) {
+			fl6_sock_release(flowlabel);
+			return err;
+		}
+		if ((fl6.flowlabel & IPV6_FLOWLABEL_MASK) && !flowlabel) {
+			flowlabel = fl6_sock_lookup(sk, fl6.flowlabel);
+			if (flowlabel == NULL)
+				return -EINVAL;
+		}
+		if (!(opt->opt_nflen|opt->opt_flen))
+			opt = NULL;
+	}
+
+	if (opt == NULL)
+		opt = np->opt;
+	if (flowlabel)
+		opt = fl6_merge_options(&opt_space, flowlabel, opt);
+	opt = ipv6_fixup_options(&opt_space, opt);
+
+	fl6.flowi6_proto = sk->sk_protocol;
+	if (!ipv6_addr_any(daddr))
+		fl6.daddr = *daddr;
+	else
+		fl6.daddr.s6_addr[15] = 0x1; /* :: means loopback (BSD'ism) */
+	if (ipv6_addr_any(&fl6.saddr) && !ipv6_addr_any(&np->saddr))
+		fl6.saddr = np->saddr;
+
+	final_p = fl6_update_dst(&fl6, opt, &final);
+
+	if (!fl6.flowi6_oif && ipv6_addr_is_multicast(&fl6.daddr))
+		fl6.flowi6_oif = np->mcast_oif;
+	else if (!fl6.flowi6_oif)
+		fl6.flowi6_oif = np->ucast_oif;
+
+	security_sk_classify_flow(sk, flowi6_to_flowi(&fl6));
+
+	dst = ip6_dst_lookup_flow(sk, &fl6, final_p, true);
+	if (IS_ERR(dst)) {
+		err = PTR_ERR(dst);
+		goto out;
+	}
+
+	if (hlimit < 0) {
+		if (ipv6_addr_is_multicast(&fl6.daddr))
+			hlimit = np->mcast_hops;
+		else
+			hlimit = np->hop_limit;
+		if (hlimit < 0)
+			hlimit = ip6_dst_hoplimit(dst);
+	}
+
+	if (tclass < 0)
+		tclass = np->tclass;
+
+	if (dontfrag < 0)
+		dontfrag = np->dontfrag;
+
+	if (msg->msg_flags & MSG_CONFIRM)
+		goto do_confirm;
+
+back_from_confirm:
+	lock_sock(sk);
+	err = ip6_append_data(sk, ip_generic_getfrag, msg->msg_iov,
+			      ulen, transhdrlen, hlimit, tclass, opt,
+			      &fl6, (struct rt6_info *)dst,
+			      msg->msg_flags, dontfrag);
+	if (err)
+		ip6_flush_pending_frames(sk);
+	else if (!(msg->msg_flags & MSG_MORE))
+		err = l2tp_ip6_push_pending_frames(sk);
+	release_sock(sk);
+done:
+	dst_release(dst);
+out:
+	fl6_sock_release(flowlabel);
+
+	return err < 0 ? err : len;
+
+do_confirm:
+	dst_confirm(dst);
+	if (!(msg->msg_flags & MSG_PROBE) || len)
+		goto back_from_confirm;
+	err = 0;
+	goto done;
+}
+
+static int l2tp_ip6_recvmsg(struct kiocb *iocb, struct sock *sk,
+			    struct msghdr *msg, size_t len, int noblock,
+			    int flags, int *addr_len)
+{
+	struct inet_sock *inet = inet_sk(sk);
+	struct sockaddr_l2tpip6 *lsa = (struct sockaddr_l2tpip6 *)msg->msg_name;
+	size_t copied = 0;
+	int err = -EOPNOTSUPP;
+	struct sk_buff *skb;
+
+	if (flags & MSG_OOB)
+		goto out;
+
+	if (addr_len)
+		*addr_len = sizeof(*lsa);
+
+	if (flags & MSG_ERRQUEUE)
+		return ipv6_recv_error(sk, msg, len);
+
+	skb = skb_recv_datagram(sk, flags, noblock, &err);
+	if (!skb)
+		goto out;
+
+	copied = skb->len;
+	if (len < copied) {
+		msg->msg_flags |= MSG_TRUNC;
+		copied = len;
+	}
+
+	err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, copied);
+	if (err)
+		goto done;
+
+	sock_recv_timestamp(msg, sk, skb);
+
+	/* Copy the address. */
+	if (lsa) {
+		lsa->l2tp_family = AF_INET6;
+		lsa->l2tp_unused = 0;
+		lsa->l2tp_addr = ipv6_hdr(skb)->saddr;
+		lsa->l2tp_flowinfo = 0;
+		lsa->l2tp_scope_id = 0;
+		if (ipv6_addr_type(&lsa->l2tp_addr) & IPV6_ADDR_LINKLOCAL)
+			lsa->l2tp_scope_id = IP6CB(skb)->iif;
+	}
+
+	if (inet->cmsg_flags)
+		ip_cmsg_recv(msg, skb);
+
+	if (flags & MSG_TRUNC)
+		copied = skb->len;
+done:
+	skb_free_datagram(sk, skb);
+out:
+	return err ? err : copied;
+}
+
+static struct proto l2tp_ip6_prot = {
+	.name		   = "L2TP/IPv6",
+	.owner		   = THIS_MODULE,
+	.init		   = l2tp_ip6_open,
+	.close		   = l2tp_ip6_close,
+	.bind		   = l2tp_ip6_bind,
+	.connect	   = l2tp_ip6_connect,
+	.disconnect	   = udp_disconnect,
+	.ioctl		   = udp_ioctl,
+	.destroy	   = l2tp_ip6_destroy_sock,
+	.setsockopt	   = ipv6_setsockopt,
+	.getsockopt	   = ipv6_getsockopt,
+	.sendmsg	   = l2tp_ip6_sendmsg,
+	.recvmsg	   = l2tp_ip6_recvmsg,
+	.backlog_rcv	   = l2tp_ip6_backlog_recv,
+	.hash		   = inet_hash,
+	.unhash		   = inet_unhash,
+	.obj_size	   = sizeof(struct l2tp_ip6_sock),
+#ifdef CONFIG_COMPAT
+	.compat_setsockopt = compat_ipv6_setsockopt,
+	.compat_getsockopt = compat_ipv6_getsockopt,
+#endif
+};
+
+static const struct proto_ops l2tp_ip6_ops = {
+	.family		   = PF_INET6,
+	.owner		   = THIS_MODULE,
+	.release	   = inet6_release,
+	.bind		   = inet6_bind,
+	.connect	   = inet_dgram_connect,
+	.socketpair	   = sock_no_socketpair,
+	.accept		   = sock_no_accept,
+	.getname	   = l2tp_ip6_getname,
+	.poll		   = datagram_poll,
+	.ioctl		   = inet6_ioctl,
+	.listen		   = sock_no_listen,
+	.shutdown	   = inet_shutdown,
+	.setsockopt	   = sock_common_setsockopt,
+	.getsockopt	   = sock_common_getsockopt,
+	.sendmsg	   = inet_sendmsg,
+	.recvmsg	   = sock_common_recvmsg,
+	.mmap		   = sock_no_mmap,
+	.sendpage	   = sock_no_sendpage,
+#ifdef CONFIG_COMPAT
+	.compat_setsockopt = compat_sock_common_setsockopt,
+	.compat_getsockopt = compat_sock_common_getsockopt,
+#endif
+};
+
+static struct inet_protosw l2tp_ip6_protosw = {
+	.type		= SOCK_DGRAM,
+	.protocol	= IPPROTO_L2TP,
+	.prot		= &l2tp_ip6_prot,
+	.ops		= &l2tp_ip6_ops,
+	.no_check	= 0,
+};
+
+static struct inet6_protocol l2tp_ip6_protocol __read_mostly = {
+	.handler	= l2tp_ip6_recv,
+};
+
+static int __init l2tp_ip6_init(void)
+{
+	int err;
+
+	printk(KERN_INFO "L2TP IP encapsulation support for IPv6 (L2TPv3)\n");
+
+	err = proto_register(&l2tp_ip6_prot, 1);
+	if (err != 0)
+		goto out;
+
+	err = inet6_add_protocol(&l2tp_ip6_protocol, IPPROTO_L2TP);
+	if (err)
+		goto out1;
+
+	inet6_register_protosw(&l2tp_ip6_protosw);
+	return 0;
+
+out1:
+	proto_unregister(&l2tp_ip6_prot);
+out:
+	return err;
+}
+
+static void __exit l2tp_ip6_exit(void)
+{
+	inet6_unregister_protosw(&l2tp_ip6_protosw);
+	inet6_del_protocol(&l2tp_ip6_protocol, IPPROTO_L2TP);
+	proto_unregister(&l2tp_ip6_prot);
+}
+
+module_init(l2tp_ip6_init);
+module_exit(l2tp_ip6_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Chris Elston <[e-mail]>");
+MODULE_DESCRIPTION("L2TP IP encapsulation for IPv6");
+MODULE_VERSION("1.0");
+
+/* Use the value of SOCK_DGRAM (2) directory, because __stringify doesn't like
+ * enums
+ */
+MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET6, 2, IPPROTO_L2TP);