l2tp: Add L2TPv3 IP encapsulation (no UDP) support

This patch adds a new L2TPIP socket family and modifies the core to
handle the case where there is no UDP header in the L2TP
packet. L2TP/IP uses IP protocol 115. Since L2TP/UDP and L2TP/IP
packets differ in layout, the datapath packet handling code needs
changes too. Userspace uses an L2TPIP socket instead of a UDP socket
when IP encapsulation is required.

We can't use raw sockets for this because the semantics of raw sockets
don't lend themselves to the socket-per-tunnel model - we need to

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 679 insertions, 0 deletions

diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
new file mode 100644
index 000000000000..75bf784ba18d
--- /dev/null
+++ b/net/l2tp/l2tp_ip.c
@@ -0,0 +1,679 @@
+/*
+ * L2TPv3 IP encapsulation support
+ *
+ * Copyright (c) 2008,2009,2010 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 <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 "l2tp_core.h"
+
+struct l2tp_ip_sock {
+        /* inet_sock has to be the first member of l2tp_ip_sock */
+        struct inet_sock        inet;
+
+        __u32                   conn_id;
+        __u32                   peer_conn_id;
+
+        __u64                   tx_packets;
+        __u64                   tx_bytes;
+        __u64                   tx_errors;
+        __u64                   rx_packets;
+        __u64                   rx_bytes;
+        __u64                   rx_errors;
+};
+
+static DEFINE_RWLOCK(l2tp_ip_lock);
+static struct hlist_head l2tp_ip_table;
+static struct hlist_head l2tp_ip_bind_table;
+
+static inline struct l2tp_ip_sock *l2tp_ip_sk(const struct sock *sk)
+{
+        return (struct l2tp_ip_sock *)sk;
+}
+
+static struct sock *__l2tp_ip_bind_lookup(struct net *net, __be32 laddr, int dif, u32 tunnel_id)
+{
+        struct hlist_node *node;
+        struct sock *sk;
+
+        sk_for_each_bound(sk, node, &l2tp_ip_bind_table) {
+                struct inet_sock *inet = inet_sk(sk);
+                struct l2tp_ip_sock *l2tp = l2tp_ip_sk(sk);
+
+                if (l2tp == NULL)
+                        continue;
+
+                if ((l2tp->conn_id == tunnel_id) &&
+#ifdef CONFIG_NET_NS
+                    (sk->sk_net == net) &&
+#endif
+                    !(inet->inet_rcv_saddr && inet->inet_rcv_saddr != laddr) &&
+                    !(sk->sk_bound_dev_if && sk->sk_bound_dev_if != dif))
+                        goto found;
+        }
+
+        sk = NULL;
+found:
+        return sk;
+}
+
+static inline struct sock *l2tp_ip_bind_lookup(struct net *net, __be32 laddr, int dif, u32 tunnel_id)
+{
+        struct sock *sk = __l2tp_ip_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_ip_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 iphdr *iph = (struct iphdr *) skb_network_header(skb);
+
+                read_lock_bh(&l2tp_ip_lock);
+                sk = __l2tp_ip_bind_lookup(&init_net, iph->daddr, 0, tunnel_id);
+                read_unlock_bh(&l2tp_ip_lock);
+        }
+
+        if (sk == NULL)
+                goto discard;
+
+        sock_hold(sk);
+
+        if (!xfrm4_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_ip_open(struct sock *sk)
+{
+        /* Prevent autobind. We don't have ports. */
+        inet_sk(sk)->inet_num = IPPROTO_L2TP;
+
+        write_lock_bh(&l2tp_ip_lock);
+        sk_add_node(sk, &l2tp_ip_table);
+        write_unlock_bh(&l2tp_ip_lock);
+
+        return 0;
+}
+
+static void l2tp_ip_close(struct sock *sk, long timeout)
+{
+        write_lock_bh(&l2tp_ip_lock);
+        hlist_del_init(&sk->sk_bind_node);
+        hlist_del_init(&sk->sk_node);
+        write_unlock_bh(&l2tp_ip_lock);
+        sk_common_release(sk);
+}
+
+static void l2tp_ip_destroy_sock(struct sock *sk)
+{
+        struct sk_buff *skb;
+
+        while ((skb = __skb_dequeue_tail(&sk->sk_write_queue)) != NULL)
+                kfree_skb(skb);
+
+        sk_refcnt_debug_dec(sk);
+}
+
+static int l2tp_ip_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
+{
+        struct inet_sock *inet = inet_sk(sk);
+        struct sockaddr_l2tpip *addr = (struct sockaddr_l2tpip *) uaddr;
+        int ret = -EINVAL;
+        int chk_addr_ret;
+
+        ret = -EADDRINUSE;
+        read_lock_bh(&l2tp_ip_lock);
+        if (__l2tp_ip_bind_lookup(&init_net, addr->l2tp_addr.s_addr, sk->sk_bound_dev_if, addr->l2tp_conn_id))
+                goto out_in_use;
+
+        read_unlock_bh(&l2tp_ip_lock);
+
+        lock_sock(sk);
+        if (sk->sk_state != TCP_CLOSE || addr_len < sizeof(struct sockaddr_l2tpip))
+                goto out;
+
+        chk_addr_ret = inet_addr_type(&init_net, addr->l2tp_addr.s_addr);
+        ret = -EADDRNOTAVAIL;
+        if (addr->l2tp_addr.s_addr && chk_addr_ret != RTN_LOCAL &&
+            chk_addr_ret != RTN_MULTICAST && chk_addr_ret != RTN_BROADCAST)
+                goto out;
+
+        inet->inet_rcv_saddr = inet->inet_saddr = addr->l2tp_addr.s_addr;
+        if (chk_addr_ret == RTN_MULTICAST || chk_addr_ret == RTN_BROADCAST)
+                inet->inet_saddr = 0;  /* Use device */
+        sk_dst_reset(sk);
+
+        l2tp_ip_sk(sk)->conn_id = addr->l2tp_conn_id;
+
+        write_lock_bh(&l2tp_ip_lock);
+        sk_add_bind_node(sk, &l2tp_ip_bind_table);
+        sk_del_node_init(sk);
+        write_unlock_bh(&l2tp_ip_lock);
+        ret = 0;
+out:
+        release_sock(sk);
+
+        return ret;
+
+out_in_use:
+        read_unlock_bh(&l2tp_ip_lock);
+
+        return ret;
+}
+
+static int l2tp_ip_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
+{
+        int rc;
+        struct inet_sock *inet = inet_sk(sk);
+        struct sockaddr_l2tpip *lsa = (struct sockaddr_l2tpip *) uaddr;
+        struct rtable *rt;
+        __be32 saddr;
+        int oif;
+
+        rc = -EINVAL;
+        if (addr_len < sizeof(*lsa))
+                goto out;
+
+        rc = -EAFNOSUPPORT;
+        if (lsa->l2tp_family != AF_INET)
+                goto out;
+
+        sk_dst_reset(sk);
+
+        oif = sk->sk_bound_dev_if;
+        saddr = inet->inet_saddr;
+
+        rc = -EINVAL;
+        if (ipv4_is_multicast(lsa->l2tp_addr.s_addr))
+                goto out;
+
+        rc = ip_route_connect(&rt, lsa->l2tp_addr.s_addr, saddr,
+                              RT_CONN_FLAGS(sk), oif,
+                              IPPROTO_L2TP,
+                              0, 0, sk, 1);
+        if (rc) {
+                if (rc == -ENETUNREACH)
+                        IP_INC_STATS_BH(&init_net, IPSTATS_MIB_OUTNOROUTES);
+                goto out;
+        }
+
+        rc = -ENETUNREACH;
+        if (rt->rt_flags & (RTCF_MULTICAST | RTCF_BROADCAST)) {
+                ip_rt_put(rt);
+                goto out;
+        }
+
+        l2tp_ip_sk(sk)->peer_conn_id = lsa->l2tp_conn_id;
+
+        if (!inet->inet_saddr)
+                inet->inet_saddr = rt->rt_src;
+        if (!inet->inet_rcv_saddr)
+                inet->inet_rcv_saddr = rt->rt_src;
+        inet->inet_daddr = rt->rt_dst;
+        sk->sk_state = TCP_ESTABLISHED;
+        inet->inet_id = jiffies;
+
+        sk_dst_set(sk, &rt->u.dst);
+
+        write_lock_bh(&l2tp_ip_lock);
+        hlist_del_init(&sk->sk_bind_node);
+        sk_add_bind_node(sk, &l2tp_ip_bind_table);
+        write_unlock_bh(&l2tp_ip_lock);
+
+        rc = 0;
+out:
+        return rc;
+}
+
+static int l2tp_ip_getname(struct socket *sock, struct sockaddr *uaddr,
+                           int *uaddr_len, int peer)
+{
+        struct sock *sk         = sock->sk;
+        struct inet_sock *inet  = inet_sk(sk);
+        struct l2tp_ip_sock *lsk = l2tp_ip_sk(sk);
+        struct sockaddr_l2tpip *lsa = (struct sockaddr_l2tpip *)uaddr;
+
+        memset(lsa, 0, sizeof(*lsa));
+        lsa->l2tp_family = AF_INET;
+        if (peer) {
+                if (!inet->inet_dport)
+                        return -ENOTCONN;
+                lsa->l2tp_conn_id = lsk->peer_conn_id;
+                lsa->l2tp_addr.s_addr = inet->inet_daddr;
+        } else {
+                __be32 addr = inet->inet_rcv_saddr;
+                if (!addr)
+                        addr = inet->inet_saddr;
+                lsa->l2tp_conn_id = lsk->conn_id;
+                lsa->l2tp_addr.s_addr = addr;
+        }
+        *uaddr_len = sizeof(*lsa);
+        return 0;
+}
+
+static int l2tp_ip_backlog_recv(struct sock *sk, struct sk_buff *skb)
+{
+        int rc;
+
+        if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
+                goto drop;
+
+        nf_reset(skb);
+
+        /* 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;
+}
+
+/* Userspace will call sendmsg() on the tunnel socket to send L2TP
+ * control frames.
+ */
+static int l2tp_ip_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, size_t len)
+{
+        struct sk_buff *skb;
+        int rc;
+        struct l2tp_ip_sock *lsa = l2tp_ip_sk(sk);
+        struct inet_sock *inet = inet_sk(sk);
+        struct ip_options *opt = inet->opt;
+        struct rtable *rt = NULL;
+        int connected = 0;
+        __be32 daddr;
+
+        if (sock_flag(sk, SOCK_DEAD))
+                return -ENOTCONN;
+
+        /* Get and verify the address. */
+        if (msg->msg_name) {
+                struct sockaddr_l2tpip *lip = (struct sockaddr_l2tpip *) msg->msg_name;
+                if (msg->msg_namelen < sizeof(*lip))
+                        return -EINVAL;
+
+                if (lip->l2tp_family != AF_INET) {
+                        if (lip->l2tp_family != AF_UNSPEC)
+                                return -EAFNOSUPPORT;
+                }
+
+                daddr = lip->l2tp_addr.s_addr;
+        } else {
+                if (sk->sk_state != TCP_ESTABLISHED)
+                        return -EDESTADDRREQ;
+
+                daddr = inet->inet_daddr;
+                connected = 1;
+        }
+
+        /* Allocate a socket buffer */
+        rc = -ENOMEM;
+        skb = sock_wmalloc(sk, 2 + NET_SKB_PAD + sizeof(struct iphdr) +
+                           4 + len, 0, GFP_KERNEL);
+        if (!skb)
+                goto error;
+
+        /* Reserve space for headers, putting IP header on 4-byte boundary. */
+        skb_reserve(skb, 2 + NET_SKB_PAD);
+        skb_reset_network_header(skb);
+        skb_reserve(skb, sizeof(struct iphdr));
+        skb_reset_transport_header(skb);
+
+        /* Insert 0 session_id */
+        *((__be32 *) skb_put(skb, 4)) = 0;
+
+        /* Copy user data into skb */
+        rc = memcpy_fromiovec(skb_put(skb, len), msg->msg_iov, len);
+        if (rc < 0) {
+                kfree_skb(skb);
+                goto error;
+        }
+
+        if (connected)
+                rt = (struct rtable *) __sk_dst_check(sk, 0);
+
+        if (rt == NULL) {
+                /* Use correct destination address if we have options. */
+                if (opt && opt->srr)
+                        daddr = opt->faddr;
+
+                {
+                        struct flowi fl = { .oif = sk->sk_bound_dev_if,
+                                            .nl_u = { .ip4_u = {
+                                                        .daddr = daddr,
+                                                        .saddr = inet->inet_saddr,
+                                                        .tos = RT_CONN_FLAGS(sk) } },
+                                            .proto = sk->sk_protocol,
+                                            .flags = inet_sk_flowi_flags(sk),
+                                            .uli_u = { .ports = {
+                                                         .sport = inet->inet_sport,
+                                                         .dport = inet->inet_dport } } };
+
+                        /* If this fails, retransmit mechanism of transport layer will
+                         * keep trying until route appears or the connection times
+                         * itself out.
+                         */
+                        security_sk_classify_flow(sk, &fl);
+                        if (ip_route_output_flow(sock_net(sk), &rt, &fl, sk, 0))
+                                goto no_route;
+                }
+                sk_setup_caps(sk, &rt->u.dst);
+        }
+        skb_dst_set(skb, dst_clone(&rt->u.dst));
+
+        /* Queue the packet to IP for output */
+        rc = ip_queue_xmit(skb, 0);
+
+error:
+        /* Update stats */
+        if (rc >= 0) {
+                lsa->tx_packets++;
+                lsa->tx_bytes += len;
+                rc = len;
+        } else {
+                lsa->tx_errors++;
+        }
+
+        return rc;
+
+no_route:
+        IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTNOROUTES);
+        kfree_skb(skb);
+        return -EHOSTUNREACH;
+}
+
+static int l2tp_ip_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 l2tp_ip_sock *lsk = l2tp_ip_sk(sk);
+        size_t copied = 0;
+        int err = -EOPNOTSUPP;
+        struct sockaddr_in *sin = (struct sockaddr_in *)msg->msg_name;
+        struct sk_buff *skb;
+
+        if (flags & MSG_OOB)
+                goto out;
+
+        if (addr_len)
+                *addr_len = sizeof(*sin);
+
+        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 (sin) {
+                sin->sin_family = AF_INET;
+                sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
+                sin->sin_port = 0;
+                memset(&sin->sin_zero, 0, sizeof(sin->sin_zero));
+        }
+        if (inet->cmsg_flags)
+                ip_cmsg_recv(msg, skb);
+        if (flags & MSG_TRUNC)
+                copied = skb->len;
+done:
+        skb_free_datagram(sk, skb);
+out:
+        if (err) {
+                lsk->rx_errors++;
+                return err;
+        }
+
+        lsk->rx_packets++;
+        lsk->rx_bytes += copied;
+
+        return copied;
+}
+
+struct proto l2tp_ip_prot = {
+        .name              = "L2TP/IP",
+        .owner             = THIS_MODULE,
+        .init              = l2tp_ip_open,
+        .close             = l2tp_ip_close,
+        .bind              = l2tp_ip_bind,
+        .connect           = l2tp_ip_connect,
+        .disconnect        = udp_disconnect,
+        .ioctl             = udp_ioctl,
+        .destroy           = l2tp_ip_destroy_sock,
+        .setsockopt        = ip_setsockopt,
+        .getsockopt        = ip_getsockopt,
+        .sendmsg           = l2tp_ip_sendmsg,
+        .recvmsg           = l2tp_ip_recvmsg,
+        .backlog_rcv       = l2tp_ip_backlog_recv,
+        .hash              = inet_hash,
+        .unhash            = inet_unhash,
+        .obj_size          = sizeof(struct l2tp_ip_sock),
+#ifdef CONFIG_COMPAT
+        .compat_setsockopt = compat_ip_setsockopt,
+        .compat_getsockopt = compat_ip_getsockopt,
+#endif
+};
+
+static const struct proto_ops l2tp_ip_ops = {
+        .family            = PF_INET,
+        .owner             = THIS_MODULE,
+        .release           = inet_release,
+        .bind              = inet_bind,
+        .connect           = inet_dgram_connect,
+        .socketpair        = sock_no_socketpair,
+        .accept            = sock_no_accept,
+        .getname           = l2tp_ip_getname,
+        .poll              = datagram_poll,
+        .ioctl             = inet_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_ip_protosw = {
+        .type           = SOCK_DGRAM,
+        .protocol       = IPPROTO_L2TP,
+        .prot           = &l2tp_ip_prot,
+        .ops            = &l2tp_ip_ops,
+        .no_check       = 0,
+};
+
+static struct net_protocol l2tp_ip_protocol __read_mostly = {
+        .handler        = l2tp_ip_recv,
+};
+
+static int __init l2tp_ip_init(void)
+{
+        int err;
+
+        printk(KERN_INFO "L2TP IP encapsulation support (L2TPv3)\n");
+
+        err = proto_register(&l2tp_ip_prot, 1);
+        if (err != 0)
+                goto out;
+
+        err = inet_add_protocol(&l2tp_ip_protocol, IPPROTO_L2TP);
+        if (err)
+                goto out1;
+
+        inet_register_protosw(&l2tp_ip_protosw);
+        return 0;
+
+out1:
+        proto_unregister(&l2tp_ip_prot);
+out:
+        return err;
+}
+
+static void __exit l2tp_ip_exit(void)
+{
+        inet_unregister_protosw(&l2tp_ip_protosw);
+        inet_del_protocol(&l2tp_ip_protocol, IPPROTO_L2TP);
+        proto_unregister(&l2tp_ip_prot);
+}
+
+module_init(l2tp_ip_init);
+module_exit(l2tp_ip_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("James Chapman <jchapman@katalix.com>");
+MODULE_DESCRIPTION("L2TP over IP");
+MODULE_VERSION("1.0");
+MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET, SOCK_DGRAM, IPPROTO_L2TP);