l2tp: Split pppol2tp patch into separate l2tp and ppp parts

This patch splits the pppol2tp driver into separate L2TP and PPP parts
to prepare for L2TPv3 support. In L2TPv3, protocols other than PPP can
be carried, so this split creates a common L2TP core that will handle
the common L2TP bits which protocol support modules such as PPP will
use.

Note that the existing pppol2tp module is split into l2tp_core and
l2tp_ppp by this change.

There are no feature changes here. Internally, however, there are
significant changes, mostly to handle the separation of PPP-specific
data from the L2TP session and to provide hooks in the core for
modules like PPP to access.

Signed-off-by: James Chapman <jchapman@katalix.com>
Reviewed-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1658 insertions, 0 deletions

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
new file mode 100644
index 000000000000..baac072761aa
--- /dev/null
+++ b/net/l2tp/l2tp_ppp.c
@@ -0,0 +1,1658 @@
+/*****************************************************************************
+ * Linux PPP over L2TP (PPPoX/PPPoL2TP) Sockets
+ *
+ * PPPoX    --- Generic PPP encapsulation socket family
+ * PPPoL2TP --- PPP over L2TP (RFC 2661)
+ *
+ * Version:     2.0.0
+ *
+ * Authors:     James Chapman (jchapman@katalix.com)
+ *
+ * Based on original work by Martijn van Oosterhout <kleptog@svana.org>
+ *
+ * License:
+ *              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.
+ *
+ */
+
+/* This driver handles only L2TP data frames; control frames are handled by a
+ * userspace application.
+ *
+ * To send data in an L2TP session, userspace opens a PPPoL2TP socket and
+ * attaches it to a bound UDP socket with local tunnel_id / session_id and
+ * peer tunnel_id / session_id set. Data can then be sent or received using
+ * regular socket sendmsg() / recvmsg() calls. Kernel parameters of the socket
+ * can be read or modified using ioctl() or [gs]etsockopt() calls.
+ *
+ * When a PPPoL2TP socket is connected with local and peer session_id values
+ * zero, the socket is treated as a special tunnel management socket.
+ *
+ * Here's example userspace code to create a socket for sending/receiving data
+ * over an L2TP session:-
+ *
+ *      struct sockaddr_pppol2tp sax;
+ *      int fd;
+ *      int session_fd;
+ *
+ *      fd = socket(AF_PPPOX, SOCK_DGRAM, PX_PROTO_OL2TP);
+ *
+ *      sax.sa_family = AF_PPPOX;
+ *      sax.sa_protocol = PX_PROTO_OL2TP;
+ *      sax.pppol2tp.fd = tunnel_fd;    // bound UDP socket
+ *      sax.pppol2tp.addr.sin_addr.s_addr = addr->sin_addr.s_addr;
+ *      sax.pppol2tp.addr.sin_port = addr->sin_port;
+ *      sax.pppol2tp.addr.sin_family = AF_INET;
+ *      sax.pppol2tp.s_tunnel  = tunnel_id;
+ *      sax.pppol2tp.s_session = session_id;
+ *      sax.pppol2tp.d_tunnel  = peer_tunnel_id;
+ *      sax.pppol2tp.d_session = peer_session_id;
+ *
+ *      session_fd = connect(fd, (struct sockaddr *)&sax, sizeof(sax));
+ *
+ * A pppd plugin that allows PPP traffic to be carried over L2TP using
+ * this driver is available from the OpenL2TP project at
+ * http://openl2tp.sourceforge.net.
+ */
+
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/list.h>
+#include <linux/uaccess.h>
+
+#include <linux/kernel.h>
+#include <linux/spinlock.h>
+#include <linux/kthread.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/errno.h>
+#include <linux/jiffies.h>
+
+#include <linux/netdevice.h>
+#include <linux/net.h>
+#include <linux/inetdevice.h>
+#include <linux/skbuff.h>
+#include <linux/init.h>
+#include <linux/ip.h>
+#include <linux/udp.h>
+#include <linux/if_pppox.h>
+#include <linux/if_pppol2tp.h>
+#include <net/sock.h>
+#include <linux/ppp_channel.h>
+#include <linux/ppp_defs.h>
+#include <linux/if_ppp.h>
+#include <linux/file.h>
+#include <linux/hash.h>
+#include <linux/sort.h>
+#include <linux/proc_fs.h>
+#include <linux/nsproxy.h>
+#include <net/net_namespace.h>
+#include <net/netns/generic.h>
+#include <net/dst.h>
+#include <net/ip.h>
+#include <net/udp.h>
+#include <net/xfrm.h>
+
+#include <asm/byteorder.h>
+#include <asm/atomic.h>
+
+#include "l2tp_core.h"
+
+#define PPPOL2TP_DRV_VERSION    "V2.0"
+
+/* Space for UDP, L2TP and PPP headers */
+#define PPPOL2TP_HEADER_OVERHEAD        40
+
+#define PRINTK(_mask, _type, _lvl, _fmt, args...)                       \
+        do {                                                            \
+                if ((_mask) & (_type))                                  \
+                        printk(_lvl "PPPOL2TP: " _fmt, ##args);         \
+        } while (0)
+
+/* Number of bytes to build transmit L2TP headers.
+ * Unfortunately the size is different depending on whether sequence numbers
+ * are enabled.
+ */
+#define PPPOL2TP_L2TP_HDR_SIZE_SEQ              10
+#define PPPOL2TP_L2TP_HDR_SIZE_NOSEQ            6
+
+/* Private data of each session. This data lives at the end of struct
+ * l2tp_session, referenced via session->priv[].
+ */
+struct pppol2tp_session {
+        int                     owner;          /* pid that opened the socket */
+
+        struct sock             *sock;          /* Pointer to the session
+                                                 * PPPoX socket */
+        struct sock             *tunnel_sock;   /* Pointer to the tunnel UDP
+                                                 * socket */
+        int                     flags;          /* accessed by PPPIOCGFLAGS.
+                                                 * Unused. */
+};
+
+static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb);
+
+static struct ppp_channel_ops pppol2tp_chan_ops = { pppol2tp_xmit , NULL };
+static const struct proto_ops pppol2tp_ops;
+
+/* Helpers to obtain tunnel/session contexts from sockets.
+ */
+static inline struct l2tp_session *pppol2tp_sock_to_session(struct sock *sk)
+{
+        struct l2tp_session *session;
+
+        if (sk == NULL)
+                return NULL;
+
+        sock_hold(sk);
+        session = (struct l2tp_session *)(sk->sk_user_data);
+        if (session == NULL) {
+                sock_put(sk);
+                goto out;
+        }
+
+        BUG_ON(session->magic != L2TP_SESSION_MAGIC);
+
+out:
+        return session;
+}
+
+/*****************************************************************************
+ * Receive data handling
+ *****************************************************************************/
+
+static int pppol2tp_recv_payload_hook(struct sk_buff *skb)
+{
+        /* Skip PPP header, if present.  In testing, Microsoft L2TP clients
+         * don't send the PPP header (PPP header compression enabled), but
+         * other clients can include the header. So we cope with both cases
+         * here. The PPP header is always FF03 when using L2TP.
+         *
+         * Note that skb->data[] isn't dereferenced from a u16 ptr here since
+         * the field may be unaligned.
+         */
+        if (!pskb_may_pull(skb, 2))
+                return 1;
+
+        if ((skb->data[0] == 0xff) && (skb->data[1] == 0x03))
+                skb_pull(skb, 2);
+
+        return 0;
+}
+
+/* Receive message. This is the recvmsg for the PPPoL2TP socket.
+ */
+static int pppol2tp_recvmsg(struct kiocb *iocb, struct socket *sock,
+                            struct msghdr *msg, size_t len,
+                            int flags)
+{
+        int err;
+        struct sk_buff *skb;
+        struct sock *sk = sock->sk;
+
+        err = -EIO;
+        if (sk->sk_state & PPPOX_BOUND)
+                goto end;
+
+        msg->msg_namelen = 0;
+
+        err = 0;
+        skb = skb_recv_datagram(sk, flags & ~MSG_DONTWAIT,
+                                flags & MSG_DONTWAIT, &err);
+        if (!skb)
+                goto end;
+
+        if (len > skb->len)
+                len = skb->len;
+        else if (len < skb->len)
+                msg->msg_flags |= MSG_TRUNC;
+
+        err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, len);
+        if (likely(err == 0))
+                err = len;
+
+        kfree_skb(skb);
+end:
+        return err;
+}
+
+static void pppol2tp_recv(struct l2tp_session *session, struct sk_buff *skb, int data_len)
+{
+        struct pppol2tp_session *ps = l2tp_session_priv(session);
+        struct sock *sk = NULL;
+
+        /* If the socket is bound, send it in to PPP's input queue. Otherwise
+         * queue it on the session socket.
+         */
+        sk = ps->sock;
+        if (sk == NULL)
+                goto no_sock;
+
+        if (sk->sk_state & PPPOX_BOUND) {
+                struct pppox_sock *po;
+                PRINTK(session->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
+                       "%s: recv %d byte data frame, passing to ppp\n",
+                       session->name, data_len);
+
+                /* We need to forget all info related to the L2TP packet
+                 * gathered in the skb as we are going to reuse the same
+                 * skb for the inner packet.
+                 * Namely we need to:
+                 * - reset xfrm (IPSec) information as it applies to
+                 *   the outer L2TP packet and not to the inner one
+                 * - release the dst to force a route lookup on the inner
+                 *   IP packet since skb->dst currently points to the dst
+                 *   of the UDP tunnel
+                 * - reset netfilter information as it doesn't apply
+                 *   to the inner packet either
+                 */
+                secpath_reset(skb);
+                skb_dst_drop(skb);
+                nf_reset(skb);
+
+                po = pppox_sk(sk);
+                ppp_input(&po->chan, skb);
+        } else {
+                PRINTK(session->debug, PPPOL2TP_MSG_DATA, KERN_INFO,
+                       "%s: socket not bound\n", session->name);
+
+                /* Not bound. Nothing we can do, so discard. */
+                session->stats.rx_errors++;
+                kfree_skb(skb);
+        }
+
+        return;
+
+no_sock:
+        PRINTK(session->debug, PPPOL2TP_MSG_DATA, KERN_INFO,
+               "%s: no socket\n", session->name);
+        kfree_skb(skb);
+}
+
+static void pppol2tp_session_sock_hold(struct l2tp_session *session)
+{
+        struct pppol2tp_session *ps = l2tp_session_priv(session);
+
+        if (ps->sock)
+                sock_hold(ps->sock);
+}
+
+static void pppol2tp_session_sock_put(struct l2tp_session *session)
+{
+        struct pppol2tp_session *ps = l2tp_session_priv(session);
+
+        if (ps->sock)
+                sock_put(ps->sock);
+}
+
+/************************************************************************
+ * Transmit handling
+ ***********************************************************************/
+
+/* Tell how big L2TP headers are for a particular session. This
+ * depends on whether sequence numbers are being used.
+ */
+static inline int pppol2tp_l2tp_header_len(struct l2tp_session *session)
+{
+        if (session->send_seq)
+                return PPPOL2TP_L2TP_HDR_SIZE_SEQ;
+
+        return PPPOL2TP_L2TP_HDR_SIZE_NOSEQ;
+}
+
+/* This is the sendmsg for the PPPoL2TP pppol2tp_session socket.  We come here
+ * when a user application does a sendmsg() on the session socket. L2TP and
+ * PPP headers must be inserted into the user's data.
+ */
+static int pppol2tp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *m,
+                            size_t total_len)
+{
+        static const unsigned char ppph[2] = { 0xff, 0x03 };
+        struct sock *sk = sock->sk;
+        struct sk_buff *skb;
+        int error;
+        struct l2tp_session *session;
+        struct l2tp_tunnel *tunnel;
+        struct pppol2tp_session *ps;
+
+        error = -ENOTCONN;
+        if (sock_flag(sk, SOCK_DEAD) || !(sk->sk_state & PPPOX_CONNECTED))
+                goto error;
+
+        /* Get session and tunnel contexts */
+        error = -EBADF;
+        session = pppol2tp_sock_to_session(sk);
+        if (session == NULL)
+                goto error;
+
+        ps = l2tp_session_priv(session);
+        tunnel = l2tp_sock_to_tunnel(ps->tunnel_sock);
+        if (tunnel == NULL)
+                goto error_put_sess;
+
+        /* Allocate a socket buffer */
+        error = -ENOMEM;
+        skb = sock_wmalloc(sk, NET_SKB_PAD + sizeof(struct iphdr) +
+                           sizeof(struct udphdr) + session->hdr_len +
+                           sizeof(ppph) + total_len,
+                           0, GFP_KERNEL);
+        if (!skb)
+                goto error_put_sess_tun;
+
+        /* Reserve space for headers. */
+        skb_reserve(skb, NET_SKB_PAD);
+        skb_reset_network_header(skb);
+        skb_reserve(skb, sizeof(struct iphdr));
+        skb_reset_transport_header(skb);
+        skb_reserve(skb, sizeof(struct udphdr));
+
+        /* Add PPP header */
+        skb->data[0] = ppph[0];
+        skb->data[1] = ppph[1];
+        skb_put(skb, 2);
+
+        /* Copy user data into skb */
+        error = memcpy_fromiovec(skb->data, m->msg_iov, total_len);
+        if (error < 0) {
+                kfree_skb(skb);
+                goto error_put_sess_tun;
+        }
+        skb_put(skb, total_len);
+
+        l2tp_xmit_skb(session, skb, session->hdr_len);
+
+        sock_put(ps->tunnel_sock);
+
+        return error;
+
+error_put_sess_tun:
+        sock_put(ps->tunnel_sock);
+error_put_sess:
+        sock_put(sk);
+error:
+        return error;
+}
+
+/* Transmit function called by generic PPP driver.  Sends PPP frame
+ * over PPPoL2TP socket.
+ *
+ * This is almost the same as pppol2tp_sendmsg(), but rather than
+ * being called with a msghdr from userspace, it is called with a skb
+ * from the kernel.
+ *
+ * The supplied skb from ppp doesn't have enough headroom for the
+ * insertion of L2TP, UDP and IP headers so we need to allocate more
+ * headroom in the skb. This will create a cloned skb. But we must be
+ * careful in the error case because the caller will expect to free
+ * the skb it supplied, not our cloned skb. So we take care to always
+ * leave the original skb unfreed if we return an error.
+ */
+static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
+{
+        static const u8 ppph[2] = { 0xff, 0x03 };
+        struct sock *sk = (struct sock *) chan->private;
+        struct sock *sk_tun;
+        int hdr_len;
+        struct l2tp_session *session;
+        struct l2tp_tunnel *tunnel;
+        struct pppol2tp_session *ps;
+        int old_headroom;
+        int new_headroom;
+
+        if (sock_flag(sk, SOCK_DEAD) || !(sk->sk_state & PPPOX_CONNECTED))
+                goto abort;
+
+        /* Get session and tunnel contexts from the socket */
+        session = pppol2tp_sock_to_session(sk);
+        if (session == NULL)
+                goto abort;
+
+        ps = l2tp_session_priv(session);
+        sk_tun = ps->tunnel_sock;
+        if (sk_tun == NULL)
+                goto abort_put_sess;
+        tunnel = l2tp_sock_to_tunnel(sk_tun);
+        if (tunnel == NULL)
+                goto abort_put_sess;
+
+        /* What header length is configured for this session? */
+        hdr_len = pppol2tp_l2tp_header_len(session);
+
+        old_headroom = skb_headroom(skb);
+        if (skb_cow_head(skb, sizeof(ppph)))
+                goto abort_put_sess_tun;
+
+        new_headroom = skb_headroom(skb);
+        skb->truesize += new_headroom - old_headroom;
+
+        /* Setup PPP header */
+        __skb_push(skb, sizeof(ppph));
+        skb->data[0] = ppph[0];
+        skb->data[1] = ppph[1];
+
+        l2tp_xmit_skb(session, skb, hdr_len);
+
+        sock_put(sk_tun);
+        sock_put(sk);
+        return 1;
+
+abort_put_sess_tun:
+        sock_put(sk_tun);
+abort_put_sess:
+        sock_put(sk);
+abort:
+        /* Free the original skb */
+        kfree_skb(skb);
+        return 1;
+}
+
+/*****************************************************************************
+ * Session (and tunnel control) socket create/destroy.
+ *****************************************************************************/
+
+/* Called by l2tp_core when a session socket is being closed.
+ */
+static void pppol2tp_session_close(struct l2tp_session *session)
+{
+        struct pppol2tp_session *ps = l2tp_session_priv(session);
+        struct sock *sk = ps->sock;
+        struct sk_buff *skb;
+
+        BUG_ON(session->magic != L2TP_SESSION_MAGIC);
+
+        if (session->session_id == 0)
+                goto out;
+
+        if (sk != NULL) {
+                lock_sock(sk);
+
+                if (sk->sk_state & (PPPOX_CONNECTED | PPPOX_BOUND)) {
+                        pppox_unbind_sock(sk);
+                        sk->sk_state = PPPOX_DEAD;
+                        sk->sk_state_change(sk);
+                }
+
+                /* Purge any queued data */
+                skb_queue_purge(&sk->sk_receive_queue);
+                skb_queue_purge(&sk->sk_write_queue);
+                while ((skb = skb_dequeue(&session->reorder_q))) {
+                        kfree_skb(skb);
+                        sock_put(sk);
+                }
+
+                release_sock(sk);
+        }
+
+out:
+        return;
+}
+
+/* Really kill the session socket. (Called from sock_put() if
+ * refcnt == 0.)
+ */
+static void pppol2tp_session_destruct(struct sock *sk)
+{
+        struct l2tp_session *session;
+
+        if (sk->sk_user_data != NULL) {
+                session = sk->sk_user_data;
+                if (session == NULL)
+                        goto out;
+
+                sk->sk_user_data = NULL;
+                BUG_ON(session->magic != L2TP_SESSION_MAGIC);
+                l2tp_session_dec_refcount(session);
+        }
+
+out:
+        return;
+}
+
+/* Called when the PPPoX socket (session) is closed.
+ */
+static int pppol2tp_release(struct socket *sock)
+{
+        struct sock *sk = sock->sk;
+        struct l2tp_session *session;
+        int error;
+
+        if (!sk)
+                return 0;
+
+        error = -EBADF;
+        lock_sock(sk);
+        if (sock_flag(sk, SOCK_DEAD) != 0)
+                goto error;
+
+        pppox_unbind_sock(sk);
+
+        /* Signal the death of the socket. */
+        sk->sk_state = PPPOX_DEAD;
+        sock_orphan(sk);
+        sock->sk = NULL;
+
+        session = pppol2tp_sock_to_session(sk);
+
+        /* Purge any queued data */
+        skb_queue_purge(&sk->sk_receive_queue);
+        skb_queue_purge(&sk->sk_write_queue);
+        if (session != NULL) {
+                struct sk_buff *skb;
+                while ((skb = skb_dequeue(&session->reorder_q))) {
+                        kfree_skb(skb);
+                        sock_put(sk);
+                }
+                sock_put(sk);
+        }
+
+        release_sock(sk);
+
+        /* This will delete the session context via
+         * pppol2tp_session_destruct() if the socket's refcnt drops to
+         * zero.
+         */
+        sock_put(sk);
+
+        return 0;
+
+error:
+        release_sock(sk);
+        return error;
+}
+
+static struct proto pppol2tp_sk_proto = {
+        .name     = "PPPOL2TP",
+        .owner    = THIS_MODULE,
+        .obj_size = sizeof(struct pppox_sock),
+};
+
+static int pppol2tp_backlog_recv(struct sock *sk, struct sk_buff *skb)
+{
+        int rc;
+
+        rc = l2tp_udp_encap_recv(sk, skb);
+        if (rc)
+                kfree_skb(skb);
+
+        return NET_RX_SUCCESS;
+}
+
+/* socket() handler. Initialize a new struct sock.
+ */
+static int pppol2tp_create(struct net *net, struct socket *sock)
+{
+        int error = -ENOMEM;
+        struct sock *sk;
+
+        sk = sk_alloc(net, PF_PPPOX, GFP_KERNEL, &pppol2tp_sk_proto);
+        if (!sk)
+                goto out;
+
+        sock_init_data(sock, sk);
+
+        sock->state  = SS_UNCONNECTED;
+        sock->ops    = &pppol2tp_ops;
+
+        sk->sk_backlog_rcv = pppol2tp_backlog_recv;
+        sk->sk_protocol    = PX_PROTO_OL2TP;
+        sk->sk_family      = PF_PPPOX;
+        sk->sk_state       = PPPOX_NONE;
+        sk->sk_type        = SOCK_STREAM;
+        sk->sk_destruct    = pppol2tp_session_destruct;
+
+        error = 0;
+
+out:
+        return error;
+}
+
+/* connect() handler. Attach a PPPoX socket to a tunnel UDP socket
+ */
+static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
+                            int sockaddr_len, int flags)
+{
+        struct sock *sk = sock->sk;
+        struct sockaddr_pppol2tp *sp = (struct sockaddr_pppol2tp *) uservaddr;
+        struct pppox_sock *po = pppox_sk(sk);
+        struct l2tp_session *session = NULL;
+        struct l2tp_tunnel *tunnel;
+        struct pppol2tp_session *ps;
+        struct dst_entry *dst;
+        struct l2tp_session_cfg cfg = { 0, };
+        int error = 0;
+
+        lock_sock(sk);
+
+        error = -EINVAL;
+        if (sp->sa_protocol != PX_PROTO_OL2TP)
+                goto end;
+
+        /* Check for already bound sockets */
+        error = -EBUSY;
+        if (sk->sk_state & PPPOX_CONNECTED)
+                goto end;
+
+        /* We don't supporting rebinding anyway */
+        error = -EALREADY;
+        if (sk->sk_user_data)
+                goto end; /* socket is already attached */
+
+        /* Don't bind if s_tunnel is 0 */
+        error = -EINVAL;
+        if (sp->pppol2tp.s_tunnel == 0)
+                goto end;
+
+        /* Special case: create tunnel context if s_session and
+         * d_session is 0. Otherwise look up tunnel using supplied
+         * tunnel id.
+         */
+        if ((sp->pppol2tp.s_session == 0) && (sp->pppol2tp.d_session == 0)) {
+                error = l2tp_tunnel_create(sock_net(sk), sp->pppol2tp.fd, 2, sp->pppol2tp.s_tunnel, sp->pppol2tp.d_tunnel, NULL, &tunnel);
+                if (error < 0)
+                        goto end;
+        } else {
+                tunnel = l2tp_tunnel_find(sock_net(sk), sp->pppol2tp.s_tunnel);
+
+                /* Error if we can't find the tunnel */
+                error = -ENOENT;
+                if (tunnel == NULL)
+                        goto end;
+
+                /* Error if socket is not prepped */
+                if (tunnel->sock == NULL)
+                        goto end;
+        }
+
+        if (tunnel->recv_payload_hook == NULL)
+                tunnel->recv_payload_hook = pppol2tp_recv_payload_hook;
+
+        /* Check that this session doesn't already exist */
+        error = -EEXIST;
+        session = l2tp_session_find(tunnel, sp->pppol2tp.s_session);
+        if (session != NULL)
+                goto end;
+
+        /* Default MTU must allow space for UDP/L2TP/PPP
+         * headers.
+         */
+        cfg.mtu = cfg.mru = 1500 - PPPOL2TP_HEADER_OVERHEAD;
+        cfg.hdr_len = PPPOL2TP_L2TP_HDR_SIZE_NOSEQ;
+        cfg.debug = tunnel->debug;
+
+        /* Allocate and initialize a new session context. */
+        session = l2tp_session_create(sizeof(struct pppol2tp_session),
+                                      tunnel, sp->pppol2tp.s_session,
+                                      sp->pppol2tp.d_session, &cfg);
+        if (session == NULL) {
+                error = -ENOMEM;
+                goto end;
+        }
+
+        ps = l2tp_session_priv(session);
+        ps->owner            = current->pid;
+        ps->sock             = sk;
+        ps->tunnel_sock = tunnel->sock;
+
+        session->recv_skb       = pppol2tp_recv;
+        session->session_close  = pppol2tp_session_close;
+
+        /* We need to know each time a skb is dropped from the reorder
+         * queue.
+         */
+        session->ref = pppol2tp_session_sock_hold;
+        session->deref = pppol2tp_session_sock_put;
+
+        /* If PMTU discovery was enabled, use the MTU that was discovered */
+        dst = sk_dst_get(sk);
+        if (dst != NULL) {
+                u32 pmtu = dst_mtu(__sk_dst_get(sk));
+                if (pmtu != 0)
+                        session->mtu = session->mru = pmtu -
+                                PPPOL2TP_HEADER_OVERHEAD;
+                dst_release(dst);
+        }
+
+        /* Special case: if source & dest session_id == 0x0000, this
+         * socket is being created to manage the tunnel. Just set up
+         * the internal context for use by ioctl() and sockopt()
+         * handlers.
+         */
+        if ((session->session_id == 0) &&
+            (session->peer_session_id == 0)) {
+                error = 0;
+                goto out_no_ppp;
+        }
+
+        /* The only header we need to worry about is the L2TP
+         * header. This size is different depending on whether
+         * sequence numbers are enabled for the data channel.
+         */
+        po->chan.hdrlen = PPPOL2TP_L2TP_HDR_SIZE_NOSEQ;
+
+        po->chan.private = sk;
+        po->chan.ops     = &pppol2tp_chan_ops;
+        po->chan.mtu     = session->mtu;
+
+        error = ppp_register_net_channel(sock_net(sk), &po->chan);
+        if (error)
+                goto end;
+
+out_no_ppp:
+        /* This is how we get the session context from the socket. */
+        sk->sk_user_data = session;
+        sk->sk_state = PPPOX_CONNECTED;
+        PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+               "%s: created\n", session->name);
+
+end:
+        release_sock(sk);
+
+        return error;
+}
+
+/* getname() support.
+ */
+static int pppol2tp_getname(struct socket *sock, struct sockaddr *uaddr,
+                            int *usockaddr_len, int peer)
+{
+        int len = sizeof(struct sockaddr_pppol2tp);
+        struct sockaddr_pppol2tp sp;
+        int error = 0;
+        struct l2tp_session *session;
+        struct l2tp_tunnel *tunnel;
+        struct sock *sk = sock->sk;
+        struct inet_sock *inet;
+        struct pppol2tp_session *pls;
+
+        error = -ENOTCONN;
+        if (sk == NULL)
+                goto end;
+        if (sk->sk_state != PPPOX_CONNECTED)
+                goto end;
+
+        error = -EBADF;
+        session = pppol2tp_sock_to_session(sk);
+        if (session == NULL)
+                goto end;
+
+        pls = l2tp_session_priv(session);
+        tunnel = l2tp_sock_to_tunnel(pls->tunnel_sock);
+        if (tunnel == NULL) {
+                error = -EBADF;
+                goto end_put_sess;
+        }
+
+        memset(&sp, 0, len);
+        sp.sa_family    = AF_PPPOX;
+        sp.sa_protocol  = PX_PROTO_OL2TP;
+        sp.pppol2tp.fd  = tunnel->fd;
+        sp.pppol2tp.pid = pls->owner;
+        sp.pppol2tp.s_tunnel = tunnel->tunnel_id;
+        sp.pppol2tp.d_tunnel = tunnel->peer_tunnel_id;
+        sp.pppol2tp.s_session = session->session_id;
+        sp.pppol2tp.d_session = session->peer_session_id;
+        inet = inet_sk(sk);
+        sp.pppol2tp.addr.sin_family = AF_INET;
+        sp.pppol2tp.addr.sin_port = inet->inet_dport;
+        sp.pppol2tp.addr.sin_addr.s_addr = inet->inet_daddr;
+
+        memcpy(uaddr, &sp, len);
+
+        *usockaddr_len = len;
+
+        sock_put(pls->tunnel_sock);
+end_put_sess:
+        sock_put(sk);
+        error = 0;
+
+end:
+        return error;
+}
+
+/****************************************************************************
+ * ioctl() handlers.
+ *
+ * The PPPoX socket is created for L2TP sessions: tunnels have their own UDP
+ * sockets. However, in order to control kernel tunnel features, we allow
+ * userspace to create a special "tunnel" PPPoX socket which is used for
+ * control only.  Tunnel PPPoX sockets have session_id == 0 and simply allow
+ * the user application to issue L2TP setsockopt(), getsockopt() and ioctl()
+ * calls.
+ ****************************************************************************/
+
+static void pppol2tp_copy_stats(struct pppol2tp_ioc_stats *dest,
+                                struct l2tp_stats *stats)
+{
+        dest->tx_packets = stats->tx_packets;
+        dest->tx_bytes = stats->tx_bytes;
+        dest->tx_errors = stats->tx_errors;
+        dest->rx_packets = stats->rx_packets;
+        dest->rx_bytes = stats->rx_bytes;
+        dest->rx_seq_discards = stats->rx_seq_discards;
+        dest->rx_oos_packets = stats->rx_oos_packets;
+        dest->rx_errors = stats->rx_errors;
+}
+
+/* Session ioctl helper.
+ */
+static int pppol2tp_session_ioctl(struct l2tp_session *session,
+                                  unsigned int cmd, unsigned long arg)
+{
+        struct ifreq ifr;
+        int err = 0;
+        struct sock *sk;
+        int val = (int) arg;
+        struct pppol2tp_session *ps = l2tp_session_priv(session);
+        struct l2tp_tunnel *tunnel = session->tunnel;
+        struct pppol2tp_ioc_stats stats;
+
+        PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_DEBUG,
+               "%s: pppol2tp_session_ioctl(cmd=%#x, arg=%#lx)\n",
+               session->name, cmd, arg);
+
+        sk = ps->sock;
+        sock_hold(sk);
+
+        switch (cmd) {
+        case SIOCGIFMTU:
+                err = -ENXIO;
+                if (!(sk->sk_state & PPPOX_CONNECTED))
+                        break;
+
+                err = -EFAULT;
+                if (copy_from_user(&ifr, (void __user *) arg, sizeof(struct ifreq)))
+                        break;
+                ifr.ifr_mtu = session->mtu;
+                if (copy_to_user((void __user *) arg, &ifr, sizeof(struct ifreq)))
+                        break;
+
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: get mtu=%d\n", session->name, session->mtu);
+                err = 0;
+                break;
+
+        case SIOCSIFMTU:
+                err = -ENXIO;
+                if (!(sk->sk_state & PPPOX_CONNECTED))
+                        break;
+
+                err = -EFAULT;
+                if (copy_from_user(&ifr, (void __user *) arg, sizeof(struct ifreq)))
+                        break;
+
+                session->mtu = ifr.ifr_mtu;
+
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: set mtu=%d\n", session->name, session->mtu);
+                err = 0;
+                break;
+
+        case PPPIOCGMRU:
+                err = -ENXIO;
+                if (!(sk->sk_state & PPPOX_CONNECTED))
+                        break;
+
+                err = -EFAULT;
+                if (put_user(session->mru, (int __user *) arg))
+                        break;
+
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: get mru=%d\n", session->name, session->mru);
+                err = 0;
+                break;
+
+        case PPPIOCSMRU:
+                err = -ENXIO;
+                if (!(sk->sk_state & PPPOX_CONNECTED))
+                        break;
+
+                err = -EFAULT;
+                if (get_user(val, (int __user *) arg))
+                        break;
+
+                session->mru = val;
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: set mru=%d\n", session->name, session->mru);
+                err = 0;
+                break;
+
+        case PPPIOCGFLAGS:
+                err = -EFAULT;
+                if (put_user(ps->flags, (int __user *) arg))
+                        break;
+
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: get flags=%d\n", session->name, ps->flags);
+                err = 0;
+                break;
+
+        case PPPIOCSFLAGS:
+                err = -EFAULT;
+                if (get_user(val, (int __user *) arg))
+                        break;
+                ps->flags = val;
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: set flags=%d\n", session->name, ps->flags);
+                err = 0;
+                break;
+
+        case PPPIOCGL2TPSTATS:
+                err = -ENXIO;
+                if (!(sk->sk_state & PPPOX_CONNECTED))
+                        break;
+
+                memset(&stats, 0, sizeof(stats));
+                stats.tunnel_id = tunnel->tunnel_id;
+                stats.session_id = session->session_id;
+                pppol2tp_copy_stats(&stats, &session->stats);
+                if (copy_to_user((void __user *) arg, &stats,
+                                 sizeof(stats)))
+                        break;
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: get L2TP stats\n", session->name);
+                err = 0;
+                break;
+
+        default:
+                err = -ENOSYS;
+                break;
+        }
+
+        sock_put(sk);
+
+        return err;
+}
+
+/* Tunnel ioctl helper.
+ *
+ * Note the special handling for PPPIOCGL2TPSTATS below. If the ioctl data
+ * specifies a session_id, the session ioctl handler is called. This allows an
+ * application to retrieve session stats via a tunnel socket.
+ */
+static int pppol2tp_tunnel_ioctl(struct l2tp_tunnel *tunnel,
+                                 unsigned int cmd, unsigned long arg)
+{
+        int err = 0;
+        struct sock *sk;
+        struct pppol2tp_ioc_stats stats;
+
+        PRINTK(tunnel->debug, PPPOL2TP_MSG_CONTROL, KERN_DEBUG,
+               "%s: pppol2tp_tunnel_ioctl(cmd=%#x, arg=%#lx)\n",
+               tunnel->name, cmd, arg);
+
+        sk = tunnel->sock;
+        sock_hold(sk);
+
+        switch (cmd) {
+        case PPPIOCGL2TPSTATS:
+                err = -ENXIO;
+                if (!(sk->sk_state & PPPOX_CONNECTED))
+                        break;
+
+                if (copy_from_user(&stats, (void __user *) arg,
+                                   sizeof(stats))) {
+                        err = -EFAULT;
+                        break;
+                }
+                if (stats.session_id != 0) {
+                        /* resend to session ioctl handler */
+                        struct l2tp_session *session =
+                                l2tp_session_find(tunnel, stats.session_id);
+                        if (session != NULL)
+                                err = pppol2tp_session_ioctl(session, cmd, arg);
+                        else
+                                err = -EBADR;
+                        break;
+                }
+#ifdef CONFIG_XFRM
+                stats.using_ipsec = (sk->sk_policy[0] || sk->sk_policy[1]) ? 1 : 0;
+#endif
+                pppol2tp_copy_stats(&stats, &tunnel->stats);
+                if (copy_to_user((void __user *) arg, &stats, sizeof(stats))) {
+                        err = -EFAULT;
+                        break;
+                }
+                PRINTK(tunnel->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: get L2TP stats\n", tunnel->name);
+                err = 0;
+                break;
+
+        default:
+                err = -ENOSYS;
+                break;
+        }
+
+        sock_put(sk);
+
+        return err;
+}
+
+/* Main ioctl() handler.
+ * Dispatch to tunnel or session helpers depending on the socket.
+ */
+static int pppol2tp_ioctl(struct socket *sock, unsigned int cmd,
+                          unsigned long arg)
+{
+        struct sock *sk = sock->sk;
+        struct l2tp_session *session;
+        struct l2tp_tunnel *tunnel;
+        struct pppol2tp_session *ps;
+        int err;
+
+        if (!sk)
+                return 0;
+
+        err = -EBADF;
+        if (sock_flag(sk, SOCK_DEAD) != 0)
+                goto end;
+
+        err = -ENOTCONN;
+        if ((sk->sk_user_data == NULL) ||
+            (!(sk->sk_state & (PPPOX_CONNECTED | PPPOX_BOUND))))
+                goto end;
+
+        /* Get session context from the socket */
+        err = -EBADF;
+        session = pppol2tp_sock_to_session(sk);
+        if (session == NULL)
+                goto end;
+
+        /* Special case: if session's session_id is zero, treat ioctl as a
+         * tunnel ioctl
+         */
+        ps = l2tp_session_priv(session);
+        if ((session->session_id == 0) &&
+            (session->peer_session_id == 0)) {
+                err = -EBADF;
+                tunnel = l2tp_sock_to_tunnel(ps->tunnel_sock);
+                if (tunnel == NULL)
+                        goto end_put_sess;
+
+                err = pppol2tp_tunnel_ioctl(tunnel, cmd, arg);
+                sock_put(ps->tunnel_sock);
+                goto end_put_sess;
+        }
+
+        err = pppol2tp_session_ioctl(session, cmd, arg);
+
+end_put_sess:
+        sock_put(sk);
+end:
+        return err;
+}
+
+/*****************************************************************************
+ * setsockopt() / getsockopt() support.
+ *
+ * The PPPoX socket is created for L2TP sessions: tunnels have their own UDP
+ * sockets. In order to control kernel tunnel features, we allow userspace to
+ * create a special "tunnel" PPPoX socket which is used for control only.
+ * Tunnel PPPoX sockets have session_id == 0 and simply allow the user
+ * application to issue L2TP setsockopt(), getsockopt() and ioctl() calls.
+ *****************************************************************************/
+
+/* Tunnel setsockopt() helper.
+ */
+static int pppol2tp_tunnel_setsockopt(struct sock *sk,
+                                      struct l2tp_tunnel *tunnel,
+                                      int optname, int val)
+{
+        int err = 0;
+
+        switch (optname) {
+        case PPPOL2TP_SO_DEBUG:
+                tunnel->debug = val;
+                PRINTK(tunnel->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: set debug=%x\n", tunnel->name, tunnel->debug);
+                break;
+
+        default:
+                err = -ENOPROTOOPT;
+                break;
+        }
+
+        return err;
+}
+
+/* Session setsockopt helper.
+ */
+static int pppol2tp_session_setsockopt(struct sock *sk,
+                                       struct l2tp_session *session,
+                                       int optname, int val)
+{
+        int err = 0;
+        struct pppol2tp_session *ps = l2tp_session_priv(session);
+
+        switch (optname) {
+        case PPPOL2TP_SO_RECVSEQ:
+                if ((val != 0) && (val != 1)) {
+                        err = -EINVAL;
+                        break;
+                }
+                session->recv_seq = val ? -1 : 0;
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: set recv_seq=%d\n", session->name, session->recv_seq);
+                break;
+
+        case PPPOL2TP_SO_SENDSEQ:
+                if ((val != 0) && (val != 1)) {
+                        err = -EINVAL;
+                        break;
+                }
+                session->send_seq = val ? -1 : 0;
+                {
+                        struct sock *ssk      = ps->sock;
+                        struct pppox_sock *po = pppox_sk(ssk);
+                        po->chan.hdrlen = val ? PPPOL2TP_L2TP_HDR_SIZE_SEQ :
+                                PPPOL2TP_L2TP_HDR_SIZE_NOSEQ;
+                }
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: set send_seq=%d\n", session->name, session->send_seq);
+                break;
+
+        case PPPOL2TP_SO_LNSMODE:
+                if ((val != 0) && (val != 1)) {
+                        err = -EINVAL;
+                        break;
+                }
+                session->lns_mode = val ? -1 : 0;
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: set lns_mode=%d\n", session->name, session->lns_mode);
+                break;
+
+        case PPPOL2TP_SO_DEBUG:
+                session->debug = val;
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: set debug=%x\n", session->name, session->debug);
+                break;
+
+        case PPPOL2TP_SO_REORDERTO:
+                session->reorder_timeout = msecs_to_jiffies(val);
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: set reorder_timeout=%d\n", session->name, session->reorder_timeout);
+                break;
+
+        default:
+                err = -ENOPROTOOPT;
+                break;
+        }
+
+        return err;
+}
+
+/* Main setsockopt() entry point.
+ * Does API checks, then calls either the tunnel or session setsockopt
+ * handler, according to whether the PPPoL2TP socket is a for a regular
+ * session or the special tunnel type.
+ */
+static int pppol2tp_setsockopt(struct socket *sock, int level, int optname,
+                               char __user *optval, unsigned int optlen)
+{
+        struct sock *sk = sock->sk;
+        struct l2tp_session *session;
+        struct l2tp_tunnel *tunnel;
+        struct pppol2tp_session *ps;
+        int val;
+        int err;
+
+        if (level != SOL_PPPOL2TP)
+                return udp_prot.setsockopt(sk, level, optname, optval, optlen);
+
+        if (optlen < sizeof(int))
+                return -EINVAL;
+
+        if (get_user(val, (int __user *)optval))
+                return -EFAULT;
+
+        err = -ENOTCONN;
+        if (sk->sk_user_data == NULL)
+                goto end;
+
+        /* Get session context from the socket */
+        err = -EBADF;
+        session = pppol2tp_sock_to_session(sk);
+        if (session == NULL)
+                goto end;
+
+        /* Special case: if session_id == 0x0000, treat as operation on tunnel
+         */
+        ps = l2tp_session_priv(session);
+        if ((session->session_id == 0) &&
+            (session->peer_session_id == 0)) {
+                err = -EBADF;
+                tunnel = l2tp_sock_to_tunnel(ps->tunnel_sock);
+                if (tunnel == NULL)
+                        goto end_put_sess;
+
+                err = pppol2tp_tunnel_setsockopt(sk, tunnel, optname, val);
+                sock_put(ps->tunnel_sock);
+        } else
+                err = pppol2tp_session_setsockopt(sk, session, optname, val);
+
+        err = 0;
+
+end_put_sess:
+        sock_put(sk);
+end:
+        return err;
+}
+
+/* Tunnel getsockopt helper. Called with sock locked.
+ */
+static int pppol2tp_tunnel_getsockopt(struct sock *sk,
+                                      struct l2tp_tunnel *tunnel,
+                                      int optname, int *val)
+{
+        int err = 0;
+
+        switch (optname) {
+        case PPPOL2TP_SO_DEBUG:
+                *val = tunnel->debug;
+                PRINTK(tunnel->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: get debug=%x\n", tunnel->name, tunnel->debug);
+                break;
+
+        default:
+                err = -ENOPROTOOPT;
+                break;
+        }
+
+        return err;
+}
+
+/* Session getsockopt helper. Called with sock locked.
+ */
+static int pppol2tp_session_getsockopt(struct sock *sk,
+                                       struct l2tp_session *session,
+                                       int optname, int *val)
+{
+        int err = 0;
+
+        switch (optname) {
+        case PPPOL2TP_SO_RECVSEQ:
+                *val = session->recv_seq;
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: get recv_seq=%d\n", session->name, *val);
+                break;
+
+        case PPPOL2TP_SO_SENDSEQ:
+                *val = session->send_seq;
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: get send_seq=%d\n", session->name, *val);
+                break;
+
+        case PPPOL2TP_SO_LNSMODE:
+                *val = session->lns_mode;
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: get lns_mode=%d\n", session->name, *val);
+                break;
+
+        case PPPOL2TP_SO_DEBUG:
+                *val = session->debug;
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: get debug=%d\n", session->name, *val);
+                break;
+
+        case PPPOL2TP_SO_REORDERTO:
+                *val = (int) jiffies_to_msecs(session->reorder_timeout);
+                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+                       "%s: get reorder_timeout=%d\n", session->name, *val);
+                break;
+
+        default:
+                err = -ENOPROTOOPT;
+        }
+
+        return err;
+}
+
+/* Main getsockopt() entry point.
+ * Does API checks, then calls either the tunnel or session getsockopt
+ * handler, according to whether the PPPoX socket is a for a regular session
+ * or the special tunnel type.
+ */
+static int pppol2tp_getsockopt(struct socket *sock, int level,
+                               int optname, char __user *optval, int __user *optlen)
+{
+        struct sock *sk = sock->sk;
+        struct l2tp_session *session;
+        struct l2tp_tunnel *tunnel;
+        int val, len;
+        int err;
+        struct pppol2tp_session *ps;
+
+        if (level != SOL_PPPOL2TP)
+                return udp_prot.getsockopt(sk, level, optname, optval, optlen);
+
+        if (get_user(len, (int __user *) optlen))
+                return -EFAULT;
+
+        len = min_t(unsigned int, len, sizeof(int));
+
+        if (len < 0)
+                return -EINVAL;
+
+        err = -ENOTCONN;
+        if (sk->sk_user_data == NULL)
+                goto end;
+
+        /* Get the session context */
+        err = -EBADF;
+        session = pppol2tp_sock_to_session(sk);
+        if (session == NULL)
+                goto end;
+
+        /* Special case: if session_id == 0x0000, treat as operation on tunnel */
+        ps = l2tp_session_priv(session);
+        if ((session->session_id == 0) &&
+            (session->peer_session_id == 0)) {
+                err = -EBADF;
+                tunnel = l2tp_sock_to_tunnel(ps->tunnel_sock);
+                if (tunnel == NULL)
+                        goto end_put_sess;
+
+                err = pppol2tp_tunnel_getsockopt(sk, tunnel, optname, &val);
+                sock_put(ps->tunnel_sock);
+        } else
+                err = pppol2tp_session_getsockopt(sk, session, optname, &val);
+
+        err = -EFAULT;
+        if (put_user(len, (int __user *) optlen))
+                goto end_put_sess;
+
+        if (copy_to_user((void __user *) optval, &val, len))
+                goto end_put_sess;
+
+        err = 0;
+
+end_put_sess:
+        sock_put(sk);
+end:
+        return err;
+}
+
+/*****************************************************************************
+ * /proc filesystem for debug
+ *****************************************************************************/
+
+static unsigned int pppol2tp_net_id;
+
+#ifdef CONFIG_PROC_FS
+
+struct pppol2tp_seq_data {
+        struct seq_net_private p;
+        int tunnel_idx;                 /* current tunnel */
+        int session_idx;                /* index of session within current tunnel */
+        struct l2tp_tunnel *tunnel;
+        struct l2tp_session *session;   /* NULL means get next tunnel */
+};
+
+static void pppol2tp_next_tunnel(struct net *net, struct pppol2tp_seq_data *pd)
+{
+        pd->tunnel = l2tp_tunnel_find_nth(net, pd->tunnel_idx);
+        pd->tunnel_idx++;
+}
+
+static void pppol2tp_next_session(struct net *net, struct pppol2tp_seq_data *pd)
+{
+        pd->session = l2tp_session_find_nth(pd->tunnel, pd->session_idx);
+        pd->session_idx++;
+        if (pd->session == NULL) {
+                pd->session_idx = 0;
+                pppol2tp_next_tunnel(net, pd);
+        }
+}
+
+static void *pppol2tp_seq_start(struct seq_file *m, loff_t *offs)
+{
+        struct pppol2tp_seq_data *pd = SEQ_START_TOKEN;
+        loff_t pos = *offs;
+        struct net *net;
+
+        if (!pos)
+                goto out;
+
+        BUG_ON(m->private == NULL);
+        pd = m->private;
+        net = seq_file_net(m);
+
+        if (pd->tunnel == NULL)
+                pppol2tp_next_tunnel(net, pd);
+        else
+                pppol2tp_next_session(net, pd);
+
+        /* NULL tunnel and session indicates end of list */
+        if ((pd->tunnel == NULL) && (pd->session == NULL))
+                pd = NULL;
+
+out:
+        return pd;
+}
+
+static void *pppol2tp_seq_next(struct seq_file *m, void *v, loff_t *pos)
+{
+        (*pos)++;
+        return NULL;
+}
+
+static void pppol2tp_seq_stop(struct seq_file *p, void *v)
+{
+        /* nothing to do */
+}
+
+static void pppol2tp_seq_tunnel_show(struct seq_file *m, void *v)
+{
+        struct l2tp_tunnel *tunnel = v;
+
+        seq_printf(m, "\nTUNNEL '%s', %c %d\n",
+                   tunnel->name,
+                   (tunnel == tunnel->sock->sk_user_data) ? 'Y' : 'N',
+                   atomic_read(&tunnel->ref_count) - 1);
+        seq_printf(m, " %08x %llu/%llu/%llu %llu/%llu/%llu\n",
+                   tunnel->debug,
+                   (unsigned long long)tunnel->stats.tx_packets,
+                   (unsigned long long)tunnel->stats.tx_bytes,
+                   (unsigned long long)tunnel->stats.tx_errors,
+                   (unsigned long long)tunnel->stats.rx_packets,
+                   (unsigned long long)tunnel->stats.rx_bytes,
+                   (unsigned long long)tunnel->stats.rx_errors);
+}
+
+static void pppol2tp_seq_session_show(struct seq_file *m, void *v)
+{
+        struct l2tp_session *session = v;
+        struct l2tp_tunnel *tunnel = session->tunnel;
+        struct pppol2tp_session *ps = l2tp_session_priv(session);
+        u32 ip = 0;
+        u16 port = 0;
+
+        if (tunnel->sock) {
+                struct inet_sock *inet = inet_sk(tunnel->sock);
+                ip = ntohl(inet->inet_saddr);
+                port = ntohs(inet->inet_sport);
+        }
+
+        seq_printf(m, "  SESSION '%s' %08X/%d %04X/%04X -> "
+                   "%04X/%04X %d %c\n",
+                   session->name, ip, port,
+                   tunnel->tunnel_id,
+                   session->session_id,
+                   tunnel->peer_tunnel_id,
+                   session->peer_session_id,
+                   ps->sock->sk_state,
+                   (session == ps->sock->sk_user_data) ?
+                   'Y' : 'N');
+        seq_printf(m, "   %d/%d/%c/%c/%s %08x %u\n",
+                   session->mtu, session->mru,
+                   session->recv_seq ? 'R' : '-',
+                   session->send_seq ? 'S' : '-',
+                   session->lns_mode ? "LNS" : "LAC",
+                   session->debug,
+                   jiffies_to_msecs(session->reorder_timeout));
+        seq_printf(m, "   %hu/%hu %llu/%llu/%llu %llu/%llu/%llu\n",
+                   session->nr, session->ns,
+                   (unsigned long long)session->stats.tx_packets,
+                   (unsigned long long)session->stats.tx_bytes,
+                   (unsigned long long)session->stats.tx_errors,
+                   (unsigned long long)session->stats.rx_packets,
+                   (unsigned long long)session->stats.rx_bytes,
+                   (unsigned long long)session->stats.rx_errors);
+}
+
+static int pppol2tp_seq_show(struct seq_file *m, void *v)
+{
+        struct pppol2tp_seq_data *pd = v;
+
+        /* display header on line 1 */
+        if (v == SEQ_START_TOKEN) {
+                seq_puts(m, "PPPoL2TP driver info, " PPPOL2TP_DRV_VERSION "\n");
+                seq_puts(m, "TUNNEL name, user-data-ok session-count\n");
+                seq_puts(m, " debug tx-pkts/bytes/errs rx-pkts/bytes/errs\n");
+                seq_puts(m, "  SESSION name, addr/port src-tid/sid "
+                         "dest-tid/sid state user-data-ok\n");
+                seq_puts(m, "   mtu/mru/rcvseq/sendseq/lns debug reorderto\n");
+                seq_puts(m, "   nr/ns tx-pkts/bytes/errs rx-pkts/bytes/errs\n");
+                goto out;
+        }
+
+        /* Show the tunnel or session context.
+         */
+        if (pd->session == NULL)
+                pppol2tp_seq_tunnel_show(m, pd->tunnel);
+        else
+                pppol2tp_seq_session_show(m, pd->session);
+
+out:
+        return 0;
+}
+
+static const struct seq_operations pppol2tp_seq_ops = {
+        .start          = pppol2tp_seq_start,
+        .next           = pppol2tp_seq_next,
+        .stop           = pppol2tp_seq_stop,
+        .show           = pppol2tp_seq_show,
+};
+
+/* Called when our /proc file is opened. We allocate data for use when
+ * iterating our tunnel / session contexts and store it in the private
+ * data of the seq_file.
+ */
+static int pppol2tp_proc_open(struct inode *inode, struct file *file)
+{
+        return seq_open_net(inode, file, &pppol2tp_seq_ops,
+                            sizeof(struct pppol2tp_seq_data));
+}
+
+static const struct file_operations pppol2tp_proc_fops = {
+        .owner          = THIS_MODULE,
+        .open           = pppol2tp_proc_open,
+        .read           = seq_read,
+        .llseek         = seq_lseek,
+        .release        = seq_release_net,
+};
+
+#endif /* CONFIG_PROC_FS */
+
+/*****************************************************************************
+ * Network namespace
+ *****************************************************************************/
+
+static __net_init int pppol2tp_init_net(struct net *net)
+{
+        struct proc_dir_entry *pde;
+        int err = 0;
+
+        pde = proc_net_fops_create(net, "pppol2tp", S_IRUGO, &pppol2tp_proc_fops);
+        if (!pde) {
+                err = -ENOMEM;
+                goto out;
+        }
+
+out:
+        return err;
+}
+
+static __net_exit void pppol2tp_exit_net(struct net *net)
+{
+        proc_net_remove(net, "pppol2tp");
+}
+
+static struct pernet_operations pppol2tp_net_ops = {
+        .init = pppol2tp_init_net,
+        .exit = pppol2tp_exit_net,
+        .id   = &pppol2tp_net_id,
+};
+
+/*****************************************************************************
+ * Init and cleanup
+ *****************************************************************************/
+
+static const struct proto_ops pppol2tp_ops = {
+        .family         = AF_PPPOX,
+        .owner          = THIS_MODULE,
+        .release        = pppol2tp_release,
+        .bind           = sock_no_bind,
+        .connect        = pppol2tp_connect,
+        .socketpair     = sock_no_socketpair,
+        .accept         = sock_no_accept,
+        .getname        = pppol2tp_getname,
+        .poll           = datagram_poll,
+        .listen         = sock_no_listen,
+        .shutdown       = sock_no_shutdown,
+        .setsockopt     = pppol2tp_setsockopt,
+        .getsockopt     = pppol2tp_getsockopt,
+        .sendmsg        = pppol2tp_sendmsg,
+        .recvmsg        = pppol2tp_recvmsg,
+        .mmap           = sock_no_mmap,
+        .ioctl          = pppox_ioctl,
+};
+
+static struct pppox_proto pppol2tp_proto = {
+        .create         = pppol2tp_create,
+        .ioctl          = pppol2tp_ioctl
+};
+
+static int __init pppol2tp_init(void)
+{
+        int err;
+
+        err = register_pernet_device(&pppol2tp_net_ops);
+        if (err)
+                goto out;
+
+        err = proto_register(&pppol2tp_sk_proto, 0);
+        if (err)
+                goto out_unregister_pppol2tp_pernet;
+
+        err = register_pppox_proto(PX_PROTO_OL2TP, &pppol2tp_proto);
+        if (err)
+                goto out_unregister_pppol2tp_proto;
+
+        printk(KERN_INFO "PPPoL2TP kernel driver, %s\n",
+               PPPOL2TP_DRV_VERSION);
+
+out:
+        return err;
+out_unregister_pppol2tp_proto:
+        proto_unregister(&pppol2tp_sk_proto);
+out_unregister_pppol2tp_pernet:
+        unregister_pernet_device(&pppol2tp_net_ops);
+        goto out;
+}
+
+static void __exit pppol2tp_exit(void)
+{
+        unregister_pppox_proto(PX_PROTO_OL2TP);
+        proto_unregister(&pppol2tp_sk_proto);
+        unregister_pernet_device(&pppol2tp_net_ops);
+}
+
+module_init(pppol2tp_init);
+module_exit(pppol2tp_exit);
+
+MODULE_AUTHOR("James Chapman <jchapman@katalix.com>");
+MODULE_DESCRIPTION("PPP over L2TP over UDP");
+MODULE_LICENSE("GPL");
+MODULE_VERSION(PPPOL2TP_DRV_VERSION);