[L2TP]: PPP over L2TP driver core

This driver handles only L2TP data frames; control frames are handled
by a userspace application. It implements L2TP using the PPPoX socket
family. There is a PPPoX socket for each L2TP session in an L2TP
tunnel.  PPP data within each session is passed through the kernel's
PPP subsystem via this driver. Kernel parameters of each socket can be
read or modified using ioctl() or [gs]etsockopt() calls.

Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/Kconfig

@@ -2784,6 +2784,19 @@ config PPPOATM
 	  which can lead to bad results if the ATM peer loses state and
 	  changes its encapsulation unilaterally.
 
+config PPPOL2TP
+	tristate "PPP over L2TP (EXPERIMENTAL)"
+	depends on EXPERIMENTAL && PPP
+	help
+	  Support for PPP-over-L2TP socket family. L2TP is a protocol
+	  used by ISPs and enterprises to tunnel PPP traffic over UDP
+	  tunnels. L2TP is replacing PPTP for VPN uses.
+
+	  This kernel component handles only L2TP data packets: a
+	  userland daemon handles L2TP the control protocol (tunnel
+	  and session setup). One such daemon is OpenL2TP
+	  (http://openl2tp.sourceforge.net/).
+
 config SLIP
 	tristate "SLIP (serial line) support"
 	---help---

drivers/net/Makefile

@@ -121,6 +121,7 @@ obj-$(CONFIG_PPP_DEFLATE) += ppp_deflate.o
 obj-$(CONFIG_PPP_BSDCOMP) += bsd_comp.o
 obj-$(CONFIG_PPP_MPPE) += ppp_mppe.o
 obj-$(CONFIG_PPPOE) += pppox.o pppoe.o
+obj-$(CONFIG_PPPOL2TP) += pppox.o pppol2tp.o
 
 obj-$(CONFIG_SLIP) += slip.o
 obj-$(CONFIG_SLHC) += slhc.o

drivers/net/pppol2tp.c

@@ -0,0 +1,2486 @@
+/*****************************************************************************
+ * Linux PPP over L2TP (PPPoX/PPPoL2TP) Sockets
+ *
+ * PPPoX    --- Generic PPP encapsulation socket family
+ * PPPoL2TP --- PPP over L2TP (RFC 2661)
+ *
+ * Version:	1.0.0
+ *
+ * Authors:	Martijn van Oosterhout <kleptog@svana.org>
+ *		James Chapman (jchapman@katalix.com)
+ * Contributors:
+ *		Michal Ostrowski <mostrows@speakeasy.net>
+ *		Arnaldo Carvalho de Melo <acme@xconectiva.com.br>
+ *		David S. Miller (davem@redhat.com)
+ *
+ * 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/version.h>
+#include <linux/string.h>
+#include <linux/list.h>
+#include <asm/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 <net/dst.h>
+#include <net/ip.h>
+#include <net/udp.h>
+#include <net/xfrm.h>
+
+#include <asm/byteorder.h>
+#include <asm/atomic.h>
+
+
+#define PPPOL2TP_DRV_VERSION	"V1.0"
+
+/* L2TP header constants */
+#define L2TP_HDRFLAG_T	   0x8000
+#define L2TP_HDRFLAG_L	   0x4000
+#define L2TP_HDRFLAG_S	   0x0800
+#define L2TP_HDRFLAG_O	   0x0200
+#define L2TP_HDRFLAG_P	   0x0100
+
+#define L2TP_HDR_VER_MASK  0x000F
+#define L2TP_HDR_VER	   0x0002
+
+/* Space for UDP, L2TP and PPP headers */
+#define PPPOL2TP_HEADER_OVERHEAD	40
+
+/* Just some random numbers */
+#define L2TP_TUNNEL_MAGIC	0x42114DDA
+#define L2TP_SESSION_MAGIC	0x0C04EB7D
+
+#define PPPOL2TP_HASH_BITS	4
+#define PPPOL2TP_HASH_SIZE	(1 << PPPOL2TP_HASH_BITS)
+
+/* Default trace flags */
+#define PPPOL2TP_DEFAULT_DEBUG_FLAGS	0
+
+#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
+
+struct pppol2tp_tunnel;
+
+/* Describes a session. It is the sk_user_data field in the PPPoL2TP
+ * socket. Contains information to determine incoming packets and transmit
+ * outgoing ones.
+ */
+struct pppol2tp_session
+{
+	int			magic;		/* should be
+						 * L2TP_SESSION_MAGIC */
+	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 */
+
+	struct pppol2tp_addr	tunnel_addr;	/* Description of tunnel */
+
+	struct pppol2tp_tunnel	*tunnel;	/* back pointer to tunnel
+						 * context */
+
+	char			name[20];	/* "sess xxxxx/yyyyy", where
+						 * x=tunnel_id, y=session_id */
+	int			mtu;
+	int			mru;
+	int			flags;		/* accessed by PPPIOCGFLAGS.
+						 * Unused. */
+	unsigned		recv_seq:1;	/* expect receive packets with
+						 * sequence numbers? */
+	unsigned		send_seq:1;	/* send packets with sequence
+						 * numbers? */
+	unsigned		lns_mode:1;	/* behave as LNS? LAC enables
+						 * sequence numbers under
+						 * control of LNS. */
+	int			debug;		/* bitmask of debug message
+						 * categories */
+	int			reorder_timeout; /* configured reorder timeout
+						  * (in jiffies) */
+	u16			nr;		/* session NR state (receive) */
+	u16			ns;		/* session NR state (send) */
+	struct sk_buff_head	reorder_q;	/* receive reorder queue */
+	struct pppol2tp_ioc_stats stats;
+	struct hlist_node	hlist;		/* Hash list node */
+};
+
+/* The sk_user_data field of the tunnel's UDP socket. It contains info to track
+ * all the associated sessions so incoming packets can be sorted out
+ */
+struct pppol2tp_tunnel
+{
+	int			magic;		/* Should be L2TP_TUNNEL_MAGIC */
+	rwlock_t		hlist_lock;	/* protect session_hlist */
+	struct hlist_head	session_hlist[PPPOL2TP_HASH_SIZE];
+						/* hashed list of sessions,
+						 * hashed by id */
+	int			debug;		/* bitmask of debug message
+						 * categories */
+	char			name[12];	/* "tunl xxxxx" */
+	struct pppol2tp_ioc_stats stats;
+
+	void (*old_sk_destruct)(struct sock *);
+
+	struct sock		*sock;		/* Parent socket */
+	struct list_head	list;		/* Keep a list of all open
+						 * prepared sockets */
+
+	atomic_t		ref_count;
+};
+
+/* Private data stored for received packets in the skb.
+ */
+struct pppol2tp_skb_cb {
+	u16			ns;
+	u16			nr;
+	u16			has_seq;
+	u16			length;
+	unsigned long		expires;
+};
+
+#define PPPOL2TP_SKB_CB(skb)	((struct pppol2tp_skb_cb *) &skb->cb[sizeof(struct inet_skb_parm)])
+
+static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb);
+static void pppol2tp_tunnel_free(struct pppol2tp_tunnel *tunnel);
+
+static atomic_t pppol2tp_tunnel_count;
+static atomic_t pppol2tp_session_count;
+static struct ppp_channel_ops pppol2tp_chan_ops = { pppol2tp_xmit , NULL };
+static struct proto_ops pppol2tp_ops;
+static LIST_HEAD(pppol2tp_tunnel_list);
+static DEFINE_RWLOCK(pppol2tp_tunnel_list_lock);
+
+/* Helpers to obtain tunnel/session contexts from sockets.
+ */
+static inline struct pppol2tp_session *pppol2tp_sock_to_session(struct sock *sk)
+{
+	struct pppol2tp_session *session;
+
+	if (sk == NULL)
+		return NULL;
+
+	session = (struct pppol2tp_session *)(sk->sk_user_data);
+	if (session == NULL)
+		return NULL;
+
+	BUG_ON(session->magic != L2TP_SESSION_MAGIC);
+
+	return session;
+}
+
+static inline struct pppol2tp_tunnel *pppol2tp_sock_to_tunnel(struct sock *sk)
+{
+	struct pppol2tp_tunnel *tunnel;
+
+	if (sk == NULL)
+		return NULL;
+
+	tunnel = (struct pppol2tp_tunnel *)(sk->sk_user_data);
+	if (tunnel == NULL)
+		return NULL;
+
+	BUG_ON(tunnel->magic != L2TP_TUNNEL_MAGIC);
+
+	return tunnel;
+}
+
+/* Tunnel reference counts. Incremented per session that is added to
+ * the tunnel.
+ */
+static inline void pppol2tp_tunnel_inc_refcount(struct pppol2tp_tunnel *tunnel)
+{
+	atomic_inc(&tunnel->ref_count);
+}
+
+static inline void pppol2tp_tunnel_dec_refcount(struct pppol2tp_tunnel *tunnel)
+{
+	if (atomic_dec_and_test(&tunnel->ref_count))
+		pppol2tp_tunnel_free(tunnel);
+}
+
+/* Session hash list.
+ * The session_id SHOULD be random according to RFC2661, but several
+ * L2TP implementations (Cisco and Microsoft) use incrementing
+ * session_ids.  So we do a real hash on the session_id, rather than a
+ * simple bitmask.
+ */
+static inline struct hlist_head *
+pppol2tp_session_id_hash(struct pppol2tp_tunnel *tunnel, u16 session_id)
+{
+	unsigned long hash_val = (unsigned long) session_id;
+	return &tunnel->session_hlist[hash_long(hash_val, PPPOL2TP_HASH_BITS)];
+}
+
+/* Lookup a session by id
+ */
+static struct pppol2tp_session *
+pppol2tp_session_find(struct pppol2tp_tunnel *tunnel, u16 session_id)
+{
+	struct hlist_head *session_list =
+		pppol2tp_session_id_hash(tunnel, session_id);
+	struct pppol2tp_session *session;
+	struct hlist_node *walk;
+
+	read_lock(&tunnel->hlist_lock);
+	hlist_for_each_entry(session, walk, session_list, hlist) {
+		if (session->tunnel_addr.s_session == session_id) {
+			read_unlock(&tunnel->hlist_lock);
+			return session;
+		}
+	}
+	read_unlock(&tunnel->hlist_lock);
+
+	return NULL;
+}
+
+/* Lookup a tunnel by id
+ */
+static struct pppol2tp_tunnel *pppol2tp_tunnel_find(u16 tunnel_id)
+{
+	struct pppol2tp_tunnel *tunnel = NULL;
+
+	read_lock(&pppol2tp_tunnel_list_lock);
+	list_for_each_entry(tunnel, &pppol2tp_tunnel_list, list) {
+		if (tunnel->stats.tunnel_id == tunnel_id) {
+			read_unlock(&pppol2tp_tunnel_list_lock);
+			return tunnel;
+		}
+	}
+	read_unlock(&pppol2tp_tunnel_list_lock);
+
+	return NULL;
+}
+
+/*****************************************************************************
+ * Receive data handling
+ *****************************************************************************/
+
+/* Queue a skb in order. We come here only if the skb has an L2TP sequence
+ * number.
+ */
+static void pppol2tp_recv_queue_skb(struct pppol2tp_session *session, struct sk_buff *skb)
+{
+	struct sk_buff *skbp;
+	u16 ns = PPPOL2TP_SKB_CB(skb)->ns;
+
+	spin_lock(&session->reorder_q.lock);
+	skb_queue_walk(&session->reorder_q, skbp) {
+		if (PPPOL2TP_SKB_CB(skbp)->ns > ns) {
+			__skb_insert(skb, skbp->prev, skbp, &session->reorder_q);
+			PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
+			       "%s: pkt %hu, inserted before %hu, reorder_q len=%d\n",
+			       session->name, ns, PPPOL2TP_SKB_CB(skbp)->ns,
+			       skb_queue_len(&session->reorder_q));
+			session->stats.rx_oos_packets++;
+			goto out;
+		}
+	}
+
+	__skb_queue_tail(&session->reorder_q, skb);
+
+out:
+	spin_unlock(&session->reorder_q.lock);
+}
+
+/* Dequeue a single skb.
+ */
+static void pppol2tp_recv_dequeue_skb(struct pppol2tp_session *session, struct sk_buff *skb)
+{
+	struct pppol2tp_tunnel *tunnel = session->tunnel;
+	int length = PPPOL2TP_SKB_CB(skb)->length;
+	struct sock *session_sock = NULL;
+
+	/* We're about to requeue the skb, so unlink it and return resources
+	 * to its current owner (a socket receive buffer).
+	 */
+	skb_unlink(skb, &session->reorder_q);
+	skb_orphan(skb);
+
+	tunnel->stats.rx_packets++;
+	tunnel->stats.rx_bytes += length;
+	session->stats.rx_packets++;
+	session->stats.rx_bytes += length;
+
+	if (PPPOL2TP_SKB_CB(skb)->has_seq) {
+		/* Bump our Nr */
+		session->nr++;
+		PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
+		       "%s: updated nr to %hu\n", session->name, session->nr);
+	}
+
+	/* If the socket is bound, send it in to PPP's input queue. Otherwise
+	 * queue it on the session socket.
+	 */
+	session_sock = session->sock;
+	if (session_sock->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, length);
+
+		/* 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);
+		dst_release(skb->dst);
+		skb->dst = NULL;
+		nf_reset(skb);
+
+		po = pppox_sk(session_sock);
+		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);
+	}
+
+	sock_put(session->sock);
+}
+
+/* Dequeue skbs from the session's reorder_q, subject to packet order.
+ * Skbs that have been in the queue for too long are simply discarded.
+ */
+static void pppol2tp_recv_dequeue(struct pppol2tp_session *session)
+{
+	struct sk_buff *skb;
+	struct sk_buff *tmp;
+
+	/* If the pkt at the head of the queue has the nr that we
+	 * expect to send up next, dequeue it and any other
+	 * in-sequence packets behind it.
+	 */
+	spin_lock(&session->reorder_q.lock);
+	skb_queue_walk_safe(&session->reorder_q, skb, tmp) {
+		if (time_after(jiffies, PPPOL2TP_SKB_CB(skb)->expires)) {
+			session->stats.rx_seq_discards++;
+			session->stats.rx_errors++;
+			PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
+			       "%s: oos pkt %hu len %d discarded (too old), "
+			       "waiting for %hu, reorder_q_len=%d\n",
+			       session->name, PPPOL2TP_SKB_CB(skb)->ns,
+			       PPPOL2TP_SKB_CB(skb)->length, session->nr,
+			       skb_queue_len(&session->reorder_q));
+			__skb_unlink(skb, &session->reorder_q);
+			kfree_skb(skb);
+			continue;
+		}
+
+		if (PPPOL2TP_SKB_CB(skb)->has_seq) {
+			if (PPPOL2TP_SKB_CB(skb)->ns != session->nr) {
+				PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
+				       "%s: holding oos pkt %hu len %d, "
+				       "waiting for %hu, reorder_q_len=%d\n",
+				       session->name, PPPOL2TP_SKB_CB(skb)->ns,
+				       PPPOL2TP_SKB_CB(skb)->length, session->nr,
+				       skb_queue_len(&session->reorder_q));
+				goto out;
+			}
+		}
+		spin_unlock(&session->reorder_q.lock);
+		pppol2tp_recv_dequeue_skb(session, skb);
+		spin_lock(&session->reorder_q.lock);
+	}
+
+out:
+	spin_unlock(&session->reorder_q.lock);
+}
+
+/* Internal receive frame. Do the real work of receiving an L2TP data frame
+ * here. The skb is not on a list when we get here.
+ * Returns 0 if the packet was a data packet and was successfully passed on.
+ * Returns 1 if the packet was not a good data packet and could not be
+ * forwarded.  All such packets are passed up to userspace to deal with.
+ */
+static int pppol2tp_recv_core(struct sock *sock, struct sk_buff *skb)
+{
+	struct pppol2tp_session *session = NULL;
+	struct pppol2tp_tunnel *tunnel;
+	unsigned char *ptr;
+	u16 hdrflags;
+	u16 tunnel_id, session_id;
+	int length;
+	struct udphdr *uh;
+
+	tunnel = pppol2tp_sock_to_tunnel(sock);
+	if (tunnel == NULL)
+		goto error;
+
+	/* Short packet? */
+	if (skb->len < sizeof(struct udphdr)) {
+		PRINTK(tunnel->debug, PPPOL2TP_MSG_DATA, KERN_INFO,
+		       "%s: recv short packet (len=%d)\n", tunnel->name, skb->len);
+		goto error;
+	}
+
+	/* Point to L2TP header */
+	ptr = skb->data + sizeof(struct udphdr);
+
+	/* Get L2TP header flags */
+	hdrflags = ntohs(*(__be16*)ptr);
+
+	/* Trace packet contents, if enabled */
+	if (tunnel->debug & PPPOL2TP_MSG_DATA) {
+		printk(KERN_DEBUG "%s: recv: ", tunnel->name);
+
+		for (length = 0; length < 16; length++)
+			printk(" %02X", ptr[length]);
+		printk("\n");
+	}
+
+	/* Get length of L2TP packet */
+	uh = (struct udphdr *) skb_transport_header(skb);
+	length = ntohs(uh->len) - sizeof(struct udphdr);
+
+	/* Too short? */
+	if (length < 12) {
+		PRINTK(tunnel->debug, PPPOL2TP_MSG_DATA, KERN_INFO,
+		       "%s: recv short L2TP packet (len=%d)\n", tunnel->name, length);
+		goto error;
+	}
+
+	/* If type is control packet, it is handled by userspace. */
+	if (hdrflags & L2TP_HDRFLAG_T) {
+		PRINTK(tunnel->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
+		       "%s: recv control packet, len=%d\n", tunnel->name, length);
+		goto error;
+	}
+
+	/* Skip flags */
+	ptr += 2;
+
+	/* If length is present, skip it */
+	if (hdrflags & L2TP_HDRFLAG_L)
+		ptr += 2;
+
+	/* Extract tunnel and session ID */
+	tunnel_id = ntohs(*(__be16 *) ptr);
+	ptr += 2;
+	session_id = ntohs(*(__be16 *) ptr);
+	ptr += 2;
+
+	/* Find the session context */
+	session = pppol2tp_session_find(tunnel, session_id);
+	if (!session) {
+		/* Not found? Pass to userspace to deal with */
+		PRINTK(tunnel->debug, PPPOL2TP_MSG_DATA, KERN_INFO,
+		       "%s: no socket found (%hu/%hu). Passing up.\n",
+		       tunnel->name, tunnel_id, session_id);
+		goto error;
+	}
+	sock_hold(session->sock);
+
+	/* The ref count on the socket was increased by the above call since
+	 * we now hold a pointer to the session. Take care to do sock_put()
+	 * when exiting this function from now on...
+	 */
+
+	/* Handle the optional sequence numbers.  If we are the LAC,
+	 * enable/disable sequence numbers under the control of the LNS.  If
+	 * no sequence numbers present but we were expecting them, discard
+	 * frame.
+	 */
+	if (hdrflags & L2TP_HDRFLAG_S) {
+		u16 ns, nr;
+		ns = ntohs(*(__be16 *) ptr);
+		ptr += 2;
+		nr = ntohs(*(__be16 *) ptr);
+		ptr += 2;
+
+		/* Received a packet with sequence numbers. If we're the LNS,
+		 * check if we sre sending sequence numbers and if not,
+		 * configure it so.
+		 */
+		if ((!session->lns_mode) && (!session->send_seq)) {
+			PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_INFO,
+			       "%s: requested to enable seq numbers by LNS\n",
+			       session->name);
+			session->send_seq = -1;
+		}
+
+		/* Store L2TP info in the skb */
+		PPPOL2TP_SKB_CB(skb)->ns = ns;
+		PPPOL2TP_SKB_CB(skb)->nr = nr;
+		PPPOL2TP_SKB_CB(skb)->has_seq = 1;
+
+		PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
+		       "%s: recv data ns=%hu, nr=%hu, session nr=%hu\n",
+		       session->name, ns, nr, session->nr);
+	} else {
+		/* No sequence numbers.
+		 * If user has configured mandatory sequence numbers, discard.
+		 */
+		if (session->recv_seq) {
+			PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_WARNING,
+			       "%s: recv data has no seq numbers when required. "
+			       "Discarding\n", session->name);
+			session->stats.rx_seq_discards++;
+			session->stats.rx_errors++;
+			goto discard;
+		}
+
+		/* If we're the LAC and we're sending sequence numbers, the
+		 * LNS has requested that we no longer send sequence numbers.
+		 * If we're the LNS and we're sending sequence numbers, the
+		 * LAC is broken. Discard the frame.
+		 */
+		if ((!session->lns_mode) && (session->send_seq)) {
+			PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_INFO,
+			       "%s: requested to disable seq numbers by LNS\n",
+			       session->name);
+			session->send_seq = 0;
+		} else if (session->send_seq) {
+			PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_WARNING,
+			       "%s: recv data has no seq numbers when required. "
+			       "Discarding\n", session->name);
+			session->stats.rx_seq_discards++;
+			session->stats.rx_errors++;
+			goto discard;
+		}
+
+		/* Store L2TP info in the skb */
+		PPPOL2TP_SKB_CB(skb)->has_seq = 0;
+	}
+
+	/* If offset bit set, skip it. */
+	if (hdrflags & L2TP_HDRFLAG_O)
+		ptr += 2 + ntohs(*(__be16 *) ptr);
+
+	skb_pull(skb, ptr - skb->data);
+
+	/* 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 ((skb->data[0] == 0xff) && (skb->data[1] == 0x03))
+		skb_pull(skb, 2);
+
+	/* Prepare skb for adding to the session's reorder_q.  Hold
+	 * packets for max reorder_timeout or 1 second if not
+	 * reordering.
+	 */
+	PPPOL2TP_SKB_CB(skb)->length = length;
+	PPPOL2TP_SKB_CB(skb)->expires = jiffies +
+		(session->reorder_timeout ? session->reorder_timeout : HZ);
+
+	/* Add packet to the session's receive queue. Reordering is done here, if
+	 * enabled. Saved L2TP protocol info is stored in skb->sb[].
+	 */
+	if (PPPOL2TP_SKB_CB(skb)->has_seq) {
+		if (session->reorder_timeout != 0) {
+			/* Packet reordering enabled. Add skb to session's
+			 * reorder queue, in order of ns.
+			 */
+			pppol2tp_recv_queue_skb(session, skb);
+		} else {
+			/* Packet reordering disabled. Discard out-of-sequence
+			 * packets
+			 */
+			if (PPPOL2TP_SKB_CB(skb)->ns != session->nr) {
+				session->stats.rx_seq_discards++;
+				session->stats.rx_errors++;
+				PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
+				       "%s: oos pkt %hu len %d discarded, "
+				       "waiting for %hu, reorder_q_len=%d\n",
+				       session->name, PPPOL2TP_SKB_CB(skb)->ns,
+				       PPPOL2TP_SKB_CB(skb)->length, session->nr,
+				       skb_queue_len(&session->reorder_q));
+				goto discard;
+			}
+			skb_queue_tail(&session->reorder_q, skb);
+		}
+	} else {
+		/* No sequence numbers. Add the skb to the tail of the
+		 * reorder queue. This ensures that it will be
+		 * delivered after all previous sequenced skbs.
+		 */
+		skb_queue_tail(&session->reorder_q, skb);
+	}
+
+	/* Try to dequeue as many skbs from reorder_q as we can. */
+	pppol2tp_recv_dequeue(session);
+
+	return 0;
+
+discard:
+	kfree_skb(skb);
+	sock_put(session->sock);
+
+	return 0;
+
+error:
+	return 1;
+}
+
+/* UDP encapsulation receive handler. See net/ipv4/udp.c.
+ * Return codes:
+ * 0 : success.
+ * <0: error
+ * >0: skb should be passed up to userspace as UDP.
+ */
+static int pppol2tp_udp_encap_recv(struct sock *sk, struct sk_buff *skb)
+{
+	struct pppol2tp_tunnel *tunnel;
+
+	tunnel = pppol2tp_sock_to_tunnel(sk);
+	if (tunnel == NULL)
+		goto pass_up;
+
+	PRINTK(tunnel->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
+	       "%s: received %d bytes\n", tunnel->name, skb->len);
+
+	if (pppol2tp_recv_core(sk, skb))
+		goto pass_up;
+
+	return 0;
+
+pass_up:
+	return 1;
+}
+
+/* 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) {
+		err = memcpy_toiovec(msg->msg_iov, (unsigned char *) skb->data,
+				     skb->len);
+		if (err < 0)
+			goto do_skb_free;
+		err = skb->len;
+	}
+do_skb_free:
+	kfree_skb(skb);
+end:
+	return err;
+}
+
+/************************************************************************
+ * 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 pppol2tp_session *session)
+{
+	if (session->send_seq)
+		return PPPOL2TP_L2TP_HDR_SIZE_SEQ;
+
+	return PPPOL2TP_L2TP_HDR_SIZE_NOSEQ;
+}
+
+/* Build an L2TP header for the session into the buffer provided.
+ */
+static void pppol2tp_build_l2tp_header(struct pppol2tp_session *session,
+				       void *buf)
+{
+	__be16 *bufp = buf;
+	u16 flags = L2TP_HDR_VER;
+
+	if (session->send_seq)
+		flags |= L2TP_HDRFLAG_S;
+
+	/* Setup L2TP header.
+	 * FIXME: Can this ever be unaligned? Is direct dereferencing of
+	 * 16-bit header fields safe here for all architectures?
+	 */
+	*bufp++ = htons(flags);
+	*bufp++ = htons(session->tunnel_addr.d_tunnel);
+	*bufp++ = htons(session->tunnel_addr.d_session);
+	if (session->send_seq) {
+		*bufp++ = htons(session->ns);
+		*bufp++ = 0;
+		session->ns++;
+		PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
+		       "%s: updated ns to %hu\n", session->name, session->ns);
+	}
+}
+
+/* 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 inet_sock *inet;
+	__wsum csum = 0;
+	struct sk_buff *skb;
+	int error;
+	int hdr_len;
+	struct pppol2tp_session *session;
+	struct pppol2tp_tunnel *tunnel;
+	struct udphdr *uh;
+
+	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;
+
+	tunnel = pppol2tp_sock_to_tunnel(session->tunnel_sock);
+	if (tunnel == NULL)
+		goto error;
+
+	/* What header length is configured for this session? */
+	hdr_len = pppol2tp_l2tp_header_len(session);
+
+	/* Allocate a socket buffer */
+	error = -ENOMEM;
+	skb = sock_wmalloc(sk, NET_SKB_PAD + sizeof(struct iphdr) +
+			   sizeof(struct udphdr) + hdr_len +
+			   sizeof(ppph) + total_len,
+			   0, GFP_KERNEL);
+	if (!skb)
+		goto error;
+
+	/* 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);
+
+	/* Build UDP header */
+	inet = inet_sk(session->tunnel_sock);
+	uh = (struct udphdr *) skb->data;
+	uh->source = inet->sport;
+	uh->dest = inet->dport;
+	uh->len = htons(hdr_len + sizeof(ppph) + total_len);
+	uh->check = 0;
+	skb_put(skb, sizeof(struct udphdr));
+
+	/* Build L2TP header */
+	pppol2tp_build_l2tp_header(session, skb->data);
+	skb_put(skb, hdr_len);
+
+	/* 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;
+	}
+	skb_put(skb, total_len);
+
+	/* Calculate UDP checksum if configured to do so */
+	if (session->tunnel_sock->sk_no_check != UDP_CSUM_NOXMIT)
+		csum = udp_csum_outgoing(sk, skb);
+
+	/* Debug */
+	if (session->send_seq)
+		PRINTK(session->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
+		       "%s: send %d bytes, ns=%hu\n", session->name,
+		       total_len, session->ns - 1);
+	else
+		PRINTK(session->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
+		       "%s: send %d bytes\n", session->name, total_len);
+
+	if (session->debug & PPPOL2TP_MSG_DATA) {
+		int i;
+		unsigned char *datap = skb->data;
+
+		printk(KERN_DEBUG "%s: xmit:", session->name);
+		for (i = 0; i < total_len; i++) {
+			printk(" %02X", *datap++);
+			if (i == 15) {
+				printk(" ...");
+				break;
+			}
+		}
+		printk("\n");
+	}
+
+	/* Queue the packet to IP for output */
+	error = ip_queue_xmit(skb, 1);
+
+	/* Update stats */
+	if (error >= 0) {
+		tunnel->stats.tx_packets++;
+		tunnel->stats.tx_bytes += skb->len;
+		session->stats.tx_packets++;
+		session->stats.tx_bytes += skb->len;
+	} else {
+		tunnel->stats.tx_errors++;
+		session->stats.tx_errors++;
+	}
+
+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 pppol2tp_session *session;
+	struct pppol2tp_tunnel *tunnel;
+	int rc;
+	int headroom;
+	int data_len = skb->len;
+	struct inet_sock *inet;
+	__wsum csum = 0;
+	struct sk_buff *skb2 = NULL;
+	struct udphdr *uh;
+
+	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;
+
+	sk_tun = session->tunnel_sock;
+	if (sk_tun == NULL)
+		goto abort;
+	tunnel = pppol2tp_sock_to_tunnel(sk_tun);
+	if (tunnel == NULL)
+		goto abort;
+
+	/* What header length is configured for this session? */
+	hdr_len = pppol2tp_l2tp_header_len(session);
+
+	/* Check that there's enough headroom in the skb to insert IP,
+	 * UDP and L2TP and PPP headers. If not enough, expand it to
+	 * make room. Note that a new skb (or a clone) is
+	 * allocated. If we return an error from this point on, make
+	 * sure we free the new skb but do not free the original skb
+	 * since that is done by the caller for the error case.
+	 */
+	headroom = NET_SKB_PAD + sizeof(struct iphdr) +
+		sizeof(struct udphdr) + hdr_len + sizeof(ppph);
+	if (skb_headroom(skb) < headroom) {
+		skb2 = skb_realloc_headroom(skb, headroom);
+		if (skb2 == NULL)
+			goto abort;
+	} else
+		skb2 = skb;
+
+	/* Check that the socket has room */
+	if (atomic_read(&sk_tun->sk_wmem_alloc) < sk_tun->sk_sndbuf)
+		skb_set_owner_w(skb2, sk_tun);
+	else
+		goto discard;
+
+	/* Setup PPP header */
+	skb_push(skb2, sizeof(ppph));
+	skb2->data[0] = ppph[0];
+	skb2->data[1] = ppph[1];
+
+	/* Setup L2TP header */
+	skb_push(skb2, hdr_len);
+	pppol2tp_build_l2tp_header(session, skb2->data);
+
+	/* Setup UDP header */
+	inet = inet_sk(sk_tun);
+	skb_push(skb2, sizeof(struct udphdr));
+	skb_reset_transport_header(skb2);
+	uh = (struct udphdr *) skb2->data;
+	uh->source = inet->sport;
+	uh->dest = inet->dport;
+	uh->len = htons(sizeof(struct udphdr) + hdr_len + sizeof(ppph) + data_len);
+	uh->check = 0;
+
+	/* Calculate UDP checksum if configured to do so */
+	if (sk_tun->sk_no_check != UDP_CSUM_NOXMIT)
+		csum = udp_csum_outgoing(sk_tun, skb2);
+
+	/* Debug */
+	if (session->send_seq)
+		PRINTK(session->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
+		       "%s: send %d bytes, ns=%hu\n", session->name,
+		       data_len, session->ns - 1);
+	else
+		PRINTK(session->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
+		       "%s: send %d bytes\n", session->name, data_len);
+
+	if (session->debug & PPPOL2TP_MSG_DATA) {
+		int i;
+		unsigned char *datap = skb2->data;
+
+		printk(KERN_DEBUG "%s: xmit:", session->name);
+		for (i = 0; i < data_len; i++) {
+			printk(" %02X", *datap++);
+			if (i == 31) {
+				printk(" ...");
+				break;
+			}
+		}
+		printk("\n");
+	}
+
+	/* Get routing info from the tunnel socket */
+	skb2->dst = sk_dst_get(sk_tun);
+
+	/* Queue the packet to IP for output */
+	rc = ip_queue_xmit(skb2, 1);
+
+	/* Update stats */
+	if (rc >= 0) {
+		tunnel->stats.tx_packets++;
+		tunnel->stats.tx_bytes += skb2->len;
+		session->stats.tx_packets++;
+		session->stats.tx_bytes += skb2->len;
+	} else {
+		tunnel->stats.tx_errors++;
+		session->stats.tx_errors++;
+	}
+
+	/* Free the original skb */
+	kfree_skb(skb);
+
+	return 1;
+
+discard:
+	/* Free the new skb. Caller will free original skb. */
+	if (skb2 != skb)
+		kfree_skb(skb2);
+abort:
+	return 0;
+}
+
+/*****************************************************************************
+ * Session (and tunnel control) socket create/destroy.
+ *****************************************************************************/
+
+/* When the tunnel UDP socket is closed, all the attached sockets need to go
+ * too.
+ */
+static void pppol2tp_tunnel_closeall(struct pppol2tp_tunnel *tunnel)
+{
+	int hash;
+	struct hlist_node *walk;
+	struct hlist_node *tmp;
+	struct pppol2tp_session *session;
+	struct sock *sk;
+
+	if (tunnel == NULL)
+		BUG();
+
+	PRINTK(tunnel->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+	       "%s: closing all sessions...\n", tunnel->name);
+
+	write_lock(&tunnel->hlist_lock);
+	for (hash = 0; hash < PPPOL2TP_HASH_SIZE; hash++) {
+again:
+		hlist_for_each_safe(walk, tmp, &tunnel->session_hlist[hash]) {
+			session = hlist_entry(walk, struct pppol2tp_session, hlist);
+
+			sk = session->sock;
+
+			PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+			       "%s: closing session\n", session->name);
+
+			hlist_del_init(&session->hlist);
+
+			/* Since we should hold the sock lock while
+			 * doing any unbinding, we need to release the
+			 * lock we're holding before taking that lock.
+			 * Hold a reference to the sock so it doesn't
+			 * disappear as we're jumping between locks.
+			 */
+			sock_hold(sk);
+			write_unlock(&tunnel->hlist_lock);
+			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);
+			skb_queue_purge(&session->reorder_q);
+
+			release_sock(sk);
+			sock_put(sk);
+
+			/* Now restart from the beginning of this hash
+			 * chain.  We always remove a session from the
+			 * list so we are guaranteed to make forward
+			 * progress.
+			 */
+			write_lock(&tunnel->hlist_lock);
+			goto again;
+		}
+	}
+	write_unlock(&tunnel->hlist_lock);
+}
+
+/* Really kill the tunnel.
+ * Come here only when all sessions have been cleared from the tunnel.
+ */
+static void pppol2tp_tunnel_free(struct pppol2tp_tunnel *tunnel)
+{
+	/* Remove from socket list */
+	write_lock(&pppol2tp_tunnel_list_lock);
+	list_del_init(&tunnel->list);
+	write_unlock(&pppol2tp_tunnel_list_lock);
+
+	atomic_dec(&pppol2tp_tunnel_count);
+	kfree(tunnel);
+}
+
+/* Tunnel UDP socket destruct hook.
+ * The tunnel context is deleted only when all session sockets have been
+ * closed.
+ */
+static void pppol2tp_tunnel_destruct(struct sock *sk)
+{
+	struct pppol2tp_tunnel *tunnel;
+
+	tunnel = pppol2tp_sock_to_tunnel(sk);
+	if (tunnel == NULL)
+		goto end;
+
+	PRINTK(tunnel->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+	       "%s: closing...\n", tunnel->name);
+
+	/* Close all sessions */
+	pppol2tp_tunnel_closeall(tunnel);
+
+	/* No longer an encapsulation socket. See net/ipv4/udp.c */
+	(udp_sk(sk))->encap_type = 0;
+	(udp_sk(sk))->encap_rcv = NULL;
+
+	/* Remove hooks into tunnel socket */
+	tunnel->sock = NULL;
+	sk->sk_destruct = tunnel->old_sk_destruct;
+	sk->sk_user_data = NULL;
+
+	/* Call original (UDP) socket descructor */
+	if (sk->sk_destruct != NULL)
+		(*sk->sk_destruct)(sk);
+
+	pppol2tp_tunnel_dec_refcount(tunnel);
+
+end:
+	return;
+}
+
+/* Really kill the session socket. (Called from sock_put() if
+ * refcnt == 0.)
+ */
+static void pppol2tp_session_destruct(struct sock *sk)
+{
+	struct pppol2tp_session *session = NULL;
+
+	if (sk->sk_user_data != NULL) {
+		struct pppol2tp_tunnel *tunnel;
+
+		session = pppol2tp_sock_to_session(sk);
+		if (session == NULL)
+			goto out;
+
+		/* Don't use pppol2tp_sock_to_tunnel() here to
+		 * get the tunnel context because the tunnel
+		 * socket might have already been closed (its
+		 * sk->sk_user_data will be NULL) so use the
+		 * session's private tunnel ptr instead.
+		 */
+		tunnel = session->tunnel;
+		if (tunnel != NULL) {
+			BUG_ON(tunnel->magic != L2TP_TUNNEL_MAGIC);
+
+			/* If session_id is zero, this is a null
+			 * session context, which was created for a
+			 * socket that is being used only to manage
+			 * tunnels.
+			 */
+			if (session->tunnel_addr.s_session != 0) {
+				/* Delete the session socket from the
+				 * hash
+				 */
+				write_lock(&tunnel->hlist_lock);
+				hlist_del_init(&session->hlist);
+				write_unlock(&tunnel->hlist_lock);
+
+				atomic_dec(&pppol2tp_session_count);
+			}
+
+			/* This will delete the tunnel context if this
+			 * is the last session on the tunnel.
+			 */
+			session->tunnel = NULL;
+			session->tunnel_sock = NULL;
+			pppol2tp_tunnel_dec_refcount(tunnel);
+		}
+	}
+
+	kfree(session);
+out:
+	return;
+}
+
+/* Called when the PPPoX socket (session) is closed.
+ */
+static int pppol2tp_release(struct socket *sock)
+{
+	struct sock *sk = sock->sk;
+	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;
+
+	/* Purge any queued data */
+	skb_queue_purge(&sk->sk_receive_queue);
+	skb_queue_purge(&sk->sk_write_queue);
+
+	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;
+}
+
+/* Internal function to prepare a tunnel (UDP) socket to have PPPoX
+ * sockets attached to it.
+ */
+static struct sock *pppol2tp_prepare_tunnel_socket(int fd, u16 tunnel_id,
+						   int *error)
+{
+	int err;
+	struct socket *sock = NULL;
+	struct sock *sk;
+	struct pppol2tp_tunnel *tunnel;
+	struct sock *ret = NULL;
+
+	/* Get the tunnel UDP socket from the fd, which was opened by
+	 * the userspace L2TP daemon.
+	 */
+	err = -EBADF;
+	sock = sockfd_lookup(fd, &err);
+	if (!sock) {
+		PRINTK(-1, PPPOL2TP_MSG_CONTROL, KERN_ERR,
+		       "tunl %hu: sockfd_lookup(fd=%d) returned %d\n",
+		       tunnel_id, fd, err);
+		goto err;
+	}
+
+	/* Quick sanity checks */
+	err = -ESOCKTNOSUPPORT;
+	if (sock->type != SOCK_DGRAM) {
+		PRINTK(-1, PPPOL2TP_MSG_CONTROL, KERN_ERR,
+		       "tunl %hu: fd %d wrong type, got %d, expected %d\n",
+		       tunnel_id, fd, sock->type, SOCK_DGRAM);
+		goto err;
+	}
+	err = -EAFNOSUPPORT;
+	if (sock->ops->family != AF_INET) {
+		PRINTK(-1, PPPOL2TP_MSG_CONTROL, KERN_ERR,
+		       "tunl %hu: fd %d wrong family, got %d, expected %d\n",
+		       tunnel_id, fd, sock->ops->family, AF_INET);
+		goto err;
+	}
+
+	err = -ENOTCONN;
+	sk = sock->sk;
+
+	/* Check if this socket has already been prepped */
+	tunnel = (struct pppol2tp_tunnel *)sk->sk_user_data;
+	if (tunnel != NULL) {
+		/* User-data field already set */
+		err = -EBUSY;
+		BUG_ON(tunnel->magic != L2TP_TUNNEL_MAGIC);
+
+		/* This socket has already been prepped */
+		ret = tunnel->sock;
+		goto out;
+	}
+
+	/* This socket is available and needs prepping. Create a new tunnel
+	 * context and init it.
+	 */
+	sk->sk_user_data = tunnel = kzalloc(sizeof(struct pppol2tp_tunnel), GFP_KERNEL);
+	if (sk->sk_user_data == NULL) {
+		err = -ENOMEM;
+		goto err;
+	}
+
+	tunnel->magic = L2TP_TUNNEL_MAGIC;
+	sprintf(&tunnel->name[0], "tunl %hu", tunnel_id);
+
+	tunnel->stats.tunnel_id = tunnel_id;
+	tunnel->debug = PPPOL2TP_DEFAULT_DEBUG_FLAGS;
+
+	/* Hook on the tunnel socket destructor so that we can cleanup
+	 * if the tunnel socket goes away.
+	 */
+	tunnel->old_sk_destruct = sk->sk_destruct;
+	sk->sk_destruct = &pppol2tp_tunnel_destruct;
+
+	tunnel->sock = sk;
+	sk->sk_allocation = GFP_ATOMIC;
+
+	/* Misc init */
+	rwlock_init(&tunnel->hlist_lock);
+
+	/* Add tunnel to our list */
+	INIT_LIST_HEAD(&tunnel->list);
+	write_lock(&pppol2tp_tunnel_list_lock);
+	list_add(&tunnel->list, &pppol2tp_tunnel_list);
+	write_unlock(&pppol2tp_tunnel_list_lock);
+	atomic_inc(&pppol2tp_tunnel_count);
+
+	/* Bump the reference count. The tunnel context is deleted
+	 * only when this drops to zero.
+	 */
+	pppol2tp_tunnel_inc_refcount(tunnel);
+
+	/* Mark socket as an encapsulation socket. See net/ipv4/udp.c */
+	(udp_sk(sk))->encap_type = UDP_ENCAP_L2TPINUDP;
+	(udp_sk(sk))->encap_rcv = pppol2tp_udp_encap_recv;
+
+	ret = tunnel->sock;
+
+	*error = 0;
+out:
+	if (sock)
+		sockfd_put(sock);
+
+	return ret;
+
+err:
+	*error = err;
+	goto out;
+}
+
+static struct proto pppol2tp_sk_proto = {
+	.name	  = "PPPOL2TP",
+	.owner	  = THIS_MODULE,
+	.obj_size = sizeof(struct pppox_sock),
+};
+
+/* socket() handler. Initialize a new struct sock.
+ */
+static int pppol2tp_create(struct socket *sock)
+{
+	int error = -ENOMEM;
+	struct sock *sk;
+
+	sk = sk_alloc(PF_PPPOX, GFP_KERNEL, &pppol2tp_sk_proto, 1);
+	if (!sk)
+		goto out;
+
+	sock_init_data(sock, sk);
+
+	sock->state  = SS_UNCONNECTED;
+	sock->ops    = &pppol2tp_ops;
+
+	sk->sk_backlog_rcv = pppol2tp_recv_core;
+	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 sock *tunnel_sock = NULL;
+	struct pppol2tp_session *session = NULL;
+	struct pppol2tp_tunnel *tunnel;
+	struct dst_entry *dst;
+	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: prepare tunnel socket 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)) {
+		tunnel_sock = pppol2tp_prepare_tunnel_socket(sp->pppol2tp.fd,
+							     sp->pppol2tp.s_tunnel,
+							     &error);
+		if (tunnel_sock == NULL)
+			goto end;
+
+		tunnel = tunnel_sock->sk_user_data;
+	} else {
+		tunnel = pppol2tp_tunnel_find(sp->pppol2tp.s_tunnel);
+
+		/* Error if we can't find the tunnel */
+		error = -ENOENT;
+		if (tunnel == NULL)
+			goto end;
+
+		tunnel_sock = tunnel->sock;
+	}
+
+	/* Check that this session doesn't already exist */
+	error = -EEXIST;
+	session = pppol2tp_session_find(tunnel, sp->pppol2tp.s_session);
+	if (session != NULL)
+		goto end;
+
+	/* Allocate and initialize a new session context. */
+	session = kzalloc(sizeof(struct pppol2tp_session), GFP_KERNEL);
+	if (session == NULL) {
+		error = -ENOMEM;
+		goto end;
+	}
+
+	skb_queue_head_init(&session->reorder_q);
+
+	session->magic	     = L2TP_SESSION_MAGIC;
+	session->owner	     = current->pid;
+	session->sock	     = sk;
+	session->tunnel	     = tunnel;
+	session->tunnel_sock = tunnel_sock;
+	session->tunnel_addr = sp->pppol2tp;
+	sprintf(&session->name[0], "sess %hu/%hu",
+		session->tunnel_addr.s_tunnel,
+		session->tunnel_addr.s_session);
+
+	session->stats.tunnel_id  = session->tunnel_addr.s_tunnel;
+	session->stats.session_id = session->tunnel_addr.s_session;
+
+	INIT_HLIST_NODE(&session->hlist);
+
+	/* Inherit debug options from tunnel */
+	session->debug = tunnel->debug;
+
+	/* Default MTU must allow space for UDP/L2TP/PPP
+	 * headers.
+	 */
+	session->mtu = session->mru = 1500 - PPPOL2TP_HEADER_OVERHEAD;
+
+	/* 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. Don't add the session to the
+	 * session hash list, just set up the internal context for use by
+	 * ioctl() and sockopt() handlers.
+	 */
+	if ((session->tunnel_addr.s_session == 0) &&
+	    (session->tunnel_addr.d_session == 0)) {
+		error = 0;
+		sk->sk_user_data = session;
+		goto out_no_ppp;
+	}
+
+	/* Get tunnel context from the tunnel socket */
+	tunnel = pppol2tp_sock_to_tunnel(tunnel_sock);
+	if (tunnel == NULL) {
+		error = -EBADF;
+		goto end;
+	}
+
+	/* Right now, because we don't have a way to push the incoming skb's
+	 * straight through the UDP layer, 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_channel(&po->chan);
+	if (error)
+		goto end;
+
+	/* This is how we get the session context from the socket. */
+	sk->sk_user_data = session;
+
+	/* Add session to the tunnel's hash list */
+	write_lock(&tunnel->hlist_lock);
+	hlist_add_head(&session->hlist,
+		       pppol2tp_session_id_hash(tunnel,
+						session->tunnel_addr.s_session));
+	write_unlock(&tunnel->hlist_lock);
+
+	atomic_inc(&pppol2tp_session_count);
+
+out_no_ppp:
+	pppol2tp_tunnel_inc_refcount(tunnel);
+	sk->sk_state = PPPOX_CONNECTED;
+	PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+	       "%s: created\n", session->name);
+
+end:
+	release_sock(sk);
+
+	if (error != 0)
+		PRINTK(session ? session->debug : -1, PPPOL2TP_MSG_CONTROL, KERN_WARNING,
+		       "%s: connect failed: %d\n", session->name, error);
+
+	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 pppol2tp_session *session;
+
+	error = -ENOTCONN;
+	if (sock->sk->sk_state != PPPOX_CONNECTED)
+		goto end;
+
+	session = pppol2tp_sock_to_session(sock->sk);
+	if (session == NULL) {
+		error = -EBADF;
+		goto end;
+	}
+
+	sp.sa_family	= AF_PPPOX;
+	sp.sa_protocol	= PX_PROTO_OL2TP;
+	memcpy(&sp.pppol2tp, &session->tunnel_addr,
+	       sizeof(struct pppol2tp_addr));
+
+	memcpy(uaddr, &sp, len);
+
+	*usockaddr_len = len;
+
+	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.
+ ****************************************************************************/
+
+/* Session ioctl helper.
+ */
+static int pppol2tp_session_ioctl(struct pppol2tp_session *session,
+				  unsigned int cmd, unsigned long arg)
+{
+	struct ifreq ifr;
+	int err = 0;
+	struct sock *sk = session->sock;
+	int val = (int) arg;
+
+	PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_DEBUG,
+	       "%s: pppol2tp_session_ioctl(cmd=%#x, arg=%#lx)\n",
+	       session->name, cmd, arg);
+
+	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(session->flags, (int __user *) arg))
+			break;
+
+		PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+		       "%s: get flags=%d\n", session->name, session->flags);
+		err = 0;
+		break;
+
+	case PPPIOCSFLAGS:
+		err = -EFAULT;
+		if (get_user(val, (int __user *) arg))
+			break;
+		session->flags = val;
+		PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+		       "%s: set flags=%d\n", session->name, session->flags);
+		err = 0;
+		break;
+
+	case PPPIOCGL2TPSTATS:
+		err = -ENXIO;
+		if (!(sk->sk_state & PPPOX_CONNECTED))
+			break;
+
+		if (copy_to_user((void __user *) arg, &session->stats,
+				 sizeof(session->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 pppol2tp_tunnel *tunnel,
+				 unsigned int cmd, unsigned long arg)
+{
+	int err = 0;
+	struct sock *sk = tunnel->sock;
+	struct pppol2tp_ioc_stats stats_req;
+
+	PRINTK(tunnel->debug, PPPOL2TP_MSG_CONTROL, KERN_DEBUG,
+	       "%s: pppol2tp_tunnel_ioctl(cmd=%#x, arg=%#lx)\n", tunnel->name,
+	       cmd, arg);
+
+	sock_hold(sk);
+
+	switch (cmd) {
+	case PPPIOCGL2TPSTATS:
+		err = -ENXIO;
+		if (!(sk->sk_state & PPPOX_CONNECTED))
+			break;
+
+		if (copy_from_user(&stats_req, (void __user *) arg,
+				   sizeof(stats_req))) {
+			err = -EFAULT;
+			break;
+		}
+		if (stats_req.session_id != 0) {
+			/* resend to session ioctl handler */
+			struct pppol2tp_session *session =
+				pppol2tp_session_find(tunnel, stats_req.session_id);
+			if (session != NULL)
+				err = pppol2tp_session_ioctl(session, cmd, arg);
+			else
+				err = -EBADR;
+			break;
+		}
+#ifdef CONFIG_XFRM
+		tunnel->stats.using_ipsec = (sk->sk_policy[0] || sk->sk_policy[1]) ? 1 : 0;
+#endif
+		if (copy_to_user((void __user *) arg, &tunnel->stats,
+				 sizeof(tunnel->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 pppol2tp_session *session;
+	struct pppol2tp_tunnel *tunnel;
+	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
+	 */
+	if ((session->tunnel_addr.s_session == 0) &&
+	    (session->tunnel_addr.d_session == 0)) {
+		err = -EBADF;
+		tunnel = pppol2tp_sock_to_tunnel(session->tunnel_sock);
+		if (tunnel == NULL)
+			goto end;
+
+		err = pppol2tp_tunnel_ioctl(tunnel, cmd, arg);
+		goto end;
+	}
+
+	err = pppol2tp_session_ioctl(session, cmd, arg);
+
+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 pppol2tp_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 pppol2tp_session *session,
+				       int optname, int val)
+{
+	int err = 0;
+
+	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      = session->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, int optlen)
+{
+	struct sock *sk = sock->sk;
+	struct pppol2tp_session *session = sk->sk_user_data;
+	struct pppol2tp_tunnel *tunnel;
+	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
+	 */
+	if ((session->tunnel_addr.s_session == 0) &&
+	    (session->tunnel_addr.d_session == 0)) {
+		err = -EBADF;
+		tunnel = pppol2tp_sock_to_tunnel(session->tunnel_sock);
+		if (tunnel == NULL)
+			goto end;
+
+		err = pppol2tp_tunnel_setsockopt(sk, tunnel, optname, val);
+	} else
+		err = pppol2tp_session_setsockopt(sk, session, optname, val);
+
+	err = 0;
+
+end:
+	return err;
+}
+
+/* Tunnel getsockopt helper. Called with sock locked.
+ */
+static int pppol2tp_tunnel_getsockopt(struct sock *sk,
+				      struct pppol2tp_tunnel *tunnel,
+				      int optname, int __user *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 pppol2tp_session *session,
+				       int optname, int __user *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 pppol2tp_session *session = sk->sk_user_data;
+	struct pppol2tp_tunnel *tunnel;
+	int val, len;
+	int err;
+
+	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 */
+	if ((session->tunnel_addr.s_session == 0) &&
+	    (session->tunnel_addr.d_session == 0)) {
+		err = -EBADF;
+		tunnel = pppol2tp_sock_to_tunnel(session->tunnel_sock);
+		if (tunnel == NULL)
+			goto end;
+
+		err = pppol2tp_tunnel_getsockopt(sk, tunnel, optname, &val);
+	} else
+		err = pppol2tp_session_getsockopt(sk, session, optname, &val);
+
+	err = -EFAULT;
+	if (put_user(len, (int __user *) optlen))
+		goto end;
+
+	if (copy_to_user((void __user *) optval, &val, len))
+		goto end;
+
+	err = 0;
+end:
+	return err;
+}
+
+/*****************************************************************************
+ * /proc filesystem for debug
+ *****************************************************************************/
+
+#ifdef CONFIG_PROC_FS
+
+#include <linux/seq_file.h>
+
+struct pppol2tp_seq_data {
+	struct pppol2tp_tunnel *tunnel; /* current tunnel */
+	struct pppol2tp_session *session; /* NULL means get first session in tunnel */
+};
+
+static struct pppol2tp_session *next_session(struct pppol2tp_tunnel *tunnel, struct pppol2tp_session *curr)
+{
+	struct pppol2tp_session *session = NULL;
+	struct hlist_node *walk;
+	int found = 0;
+	int next = 0;
+	int i;
+
+	read_lock(&tunnel->hlist_lock);
+	for (i = 0; i < PPPOL2TP_HASH_SIZE; i++) {
+		hlist_for_each_entry(session, walk, &tunnel->session_hlist[i], hlist) {
+			if (curr == NULL) {
+				found = 1;
+				goto out;
+			}
+			if (session == curr) {
+				next = 1;
+				continue;
+			}
+			if (next) {
+				found = 1;
+				goto out;
+			}
+		}
+	}
+out:
+	read_unlock(&tunnel->hlist_lock);
+	if (!found)
+		session = NULL;
+
+	return session;
+}
+
+static struct pppol2tp_tunnel *next_tunnel(struct pppol2tp_tunnel *curr)
+{
+	struct pppol2tp_tunnel *tunnel = NULL;
+
+	read_lock(&pppol2tp_tunnel_list_lock);
+	if (list_is_last(&curr->list, &pppol2tp_tunnel_list)) {
+		goto out;
+	}
+	tunnel = list_entry(curr->list.next, struct pppol2tp_tunnel, list);
+out:
+	read_unlock(&pppol2tp_tunnel_list_lock);
+
+	return tunnel;
+}
+
+static void *pppol2tp_seq_start(struct seq_file *m, loff_t *offs)
+{
+	struct pppol2tp_seq_data *pd = SEQ_START_TOKEN;
+	loff_t pos = *offs;
+
+	if (!pos)
+		goto out;
+
+	BUG_ON(m->private == NULL);
+	pd = m->private;
+
+	if (pd->tunnel == NULL) {
+		if (!list_empty(&pppol2tp_tunnel_list))
+			pd->tunnel = list_entry(pppol2tp_tunnel_list.next, struct pppol2tp_tunnel, list);
+	} else {
+		pd->session = next_session(pd->tunnel, pd->session);
+		if (pd->session == NULL) {
+			pd->tunnel = next_tunnel(pd->tunnel);
+		}
+	}
+
+	/* 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 pppol2tp_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,
+		   tunnel->stats.tx_packets, tunnel->stats.tx_bytes,
+		   tunnel->stats.tx_errors,
+		   tunnel->stats.rx_packets, tunnel->stats.rx_bytes,
+		   tunnel->stats.rx_errors);
+}
+
+static void pppol2tp_seq_session_show(struct seq_file *m, void *v)
+{
+	struct pppol2tp_session *session = v;
+
+	seq_printf(m, "  SESSION '%s' %08X/%d %04X/%04X -> "
+		   "%04X/%04X %d %c\n",
+		   session->name,
+		   ntohl(session->tunnel_addr.addr.sin_addr.s_addr),
+		   ntohs(session->tunnel_addr.addr.sin_port),
+		   session->tunnel_addr.s_tunnel,
+		   session->tunnel_addr.s_session,
+		   session->tunnel_addr.d_tunnel,
+		   session->tunnel_addr.d_session,
+		   session->sock->sk_state,
+		   (session == session->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,
+		   session->stats.tx_packets,
+		   session->stats.tx_bytes,
+		   session->stats.tx_errors,
+		   session->stats.rx_packets,
+		   session->stats.rx_bytes,
+		   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 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)
+{
+	struct seq_file *m;
+	struct pppol2tp_seq_data *pd;
+	int ret = 0;
+
+	ret = seq_open(file, &pppol2tp_seq_ops);
+	if (ret < 0)
+		goto out;
+
+	m = file->private_data;
+
+	/* Allocate and fill our proc_data for access later */
+	ret = -ENOMEM;
+	m->private = kzalloc(sizeof(struct pppol2tp_seq_data), GFP_KERNEL);
+	if (m->private == NULL)
+		goto out;
+
+	pd = m->private;
+	ret = 0;
+
+out:
+	return ret;
+}
+
+/* Called when /proc file access completes.
+ */
+static int pppol2tp_proc_release(struct inode *inode, struct file *file)
+{
+	struct seq_file *m = (struct seq_file *)file->private_data;
+
+	kfree(m->private);
+	m->private = NULL;
+
+	return seq_release(inode, file);
+}
+
+static struct file_operations pppol2tp_proc_fops = {
+	.owner		= THIS_MODULE,
+	.open		= pppol2tp_proc_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= pppol2tp_proc_release,
+};
+
+static struct proc_dir_entry *pppol2tp_proc;
+
+#endif /* CONFIG_PROC_FS */
+
+/*****************************************************************************
+ * Init and cleanup
+ *****************************************************************************/
+
+static 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 = proto_register(&pppol2tp_sk_proto, 0);
+	if (err)
+		goto out;
+	err = register_pppox_proto(PX_PROTO_OL2TP, &pppol2tp_proto);
+	if (err)
+		goto out_unregister_pppol2tp_proto;
+
+#ifdef CONFIG_PROC_FS
+	pppol2tp_proc = create_proc_entry("pppol2tp", 0, proc_net);
+	if (!pppol2tp_proc) {
+		err = -ENOMEM;
+		goto out_unregister_pppox_proto;
+	}
+	pppol2tp_proc->proc_fops = &pppol2tp_proc_fops;
+#endif /* CONFIG_PROC_FS */
+	printk(KERN_INFO "PPPoL2TP kernel driver, %s\n",
+	       PPPOL2TP_DRV_VERSION);
+
+out:
+	return err;
+
+out_unregister_pppox_proto:
+	unregister_pppox_proto(PX_PROTO_OL2TP);
+out_unregister_pppol2tp_proto:
+	proto_unregister(&pppol2tp_sk_proto);
+	goto out;
+}
+
+static void __exit pppol2tp_exit(void)
+{
+	unregister_pppox_proto(PX_PROTO_OL2TP);
+
+#ifdef CONFIG_PROC_FS
+	remove_proc_entry("pppol2tp", proc_net);
+#endif
+	proto_unregister(&pppol2tp_sk_proto);
+}
+
+module_init(pppol2tp_init);
+module_exit(pppol2tp_exit);
+
+MODULE_AUTHOR("Martijn van Oosterhout <kleptog@svana.org>,"
+	      "James Chapman <jchapman@katalix.com>");
+MODULE_DESCRIPTION("PPP over L2TP over UDP");
+MODULE_LICENSE("GPL");
+MODULE_VERSION(PPPOL2TP_DRV_VERSION);