Moved, renamed, and deleted files

The original directory structure was scattered and unorganized.
Changes are basically to make it look like kernel structure.

1 files changed, 1704 insertions, 0 deletions

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
new file mode 100644
index 00000000..89ff8c67
--- /dev/null
+++ b/net/l2tp/l2tp_core.c
@@ -0,0 +1,1704 @@
+/*
+ * L2TP core.
+ *
+ * Copyright (c) 2008,2009,2010 Katalix Systems Ltd
+ *
+ * This file contains some code of the original L2TPv2 pppol2tp
+ * driver, which has the following copyright:
+ *
+ * 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)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/list.h>
+#include <linux/rculist.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/in.h>
+#include <linux/ip.h>
+#include <linux/udp.h>
+#include <linux/l2tp.h>
+#include <linux/hash.h>
+#include <linux/sort.h>
+#include <linux/file.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/inet_common.h>
+#include <net/xfrm.h>
+#include <net/protocol.h>
+
+#include <asm/byteorder.h>
+#include <linux/atomic.h>
+
+#include "l2tp_core.h"
+
+#define L2TP_DRV_VERSION	"V2.0"
+
+/* 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_2	   0x0002
+#define L2TP_HDR_VER_3	   0x0003
+
+/* L2TPv3 default L2-specific sublayer */
+#define L2TP_SLFLAG_S	   0x40000000
+#define L2TP_SL_SEQ_MASK   0x00ffffff
+
+#define L2TP_HDR_SIZE_SEQ		10
+#define L2TP_HDR_SIZE_NOSEQ		6
+
+/* Default trace flags */
+#define L2TP_DEFAULT_DEBUG_FLAGS	0
+
+#define PRINTK(_mask, _type, _lvl, _fmt, args...)			\
+	do {								\
+		if ((_mask) & (_type))					\
+			printk(_lvl "L2TP: " _fmt, ##args);		\
+	} while (0)
+
+/* Private data stored for received packets in the skb.
+ */
+struct l2tp_skb_cb {
+	u32			ns;
+	u16			has_seq;
+	u16			length;
+	unsigned long		expires;
+};
+
+#define L2TP_SKB_CB(skb)	((struct l2tp_skb_cb *) &skb->cb[sizeof(struct inet_skb_parm)])
+
+static atomic_t l2tp_tunnel_count;
+static atomic_t l2tp_session_count;
+
+/* per-net private data for this module */
+static unsigned int l2tp_net_id;
+struct l2tp_net {
+	struct list_head l2tp_tunnel_list;
+	spinlock_t l2tp_tunnel_list_lock;
+	struct hlist_head l2tp_session_hlist[L2TP_HASH_SIZE_2];
+	spinlock_t l2tp_session_hlist_lock;
+};
+
+static void l2tp_session_set_header_len(struct l2tp_session *session, int version);
+static void l2tp_tunnel_free(struct l2tp_tunnel *tunnel);
+static void l2tp_tunnel_closeall(struct l2tp_tunnel *tunnel);
+
+static inline struct l2tp_net *l2tp_pernet(struct net *net)
+{
+	BUG_ON(!net);
+
+	return net_generic(net, l2tp_net_id);
+}
+
+
+/* Tunnel reference counts. Incremented per session that is added to
+ * the tunnel.
+ */
+static inline void l2tp_tunnel_inc_refcount_1(struct l2tp_tunnel *tunnel)
+{
+	atomic_inc(&tunnel->ref_count);
+}
+
+static inline void l2tp_tunnel_dec_refcount_1(struct l2tp_tunnel *tunnel)
+{
+	if (atomic_dec_and_test(&tunnel->ref_count))
+		l2tp_tunnel_free(tunnel);
+}
+#ifdef L2TP_REFCNT_DEBUG
+#define l2tp_tunnel_inc_refcount(_t) do { \
+		printk(KERN_DEBUG "l2tp_tunnel_inc_refcount: %s:%d %s: cnt=%d\n", __func__, __LINE__, (_t)->name, atomic_read(&_t->ref_count)); \
+		l2tp_tunnel_inc_refcount_1(_t);				\
+	} while (0)
+#define l2tp_tunnel_dec_refcount(_t) do { \
+		printk(KERN_DEBUG "l2tp_tunnel_dec_refcount: %s:%d %s: cnt=%d\n", __func__, __LINE__, (_t)->name, atomic_read(&_t->ref_count)); \
+		l2tp_tunnel_dec_refcount_1(_t);				\
+	} while (0)
+#else
+#define l2tp_tunnel_inc_refcount(t) l2tp_tunnel_inc_refcount_1(t)
+#define l2tp_tunnel_dec_refcount(t) l2tp_tunnel_dec_refcount_1(t)
+#endif
+
+/* Session hash global list for L2TPv3.
+ * The session_id SHOULD be random according to RFC3931, but several
+ * L2TP implementations use incrementing session_ids.  So we do a real
+ * hash on the session_id, rather than a simple bitmask.
+ */
+static inline struct hlist_head *
+l2tp_session_id_hash_2(struct l2tp_net *pn, u32 session_id)
+{
+	return &pn->l2tp_session_hlist[hash_32(session_id, L2TP_HASH_BITS_2)];
+
+}
+
+/* Lookup a session by id in the global session list
+ */
+static struct l2tp_session *l2tp_session_find_2(struct net *net, u32 session_id)
+{
+	struct l2tp_net *pn = l2tp_pernet(net);
+	struct hlist_head *session_list =
+		l2tp_session_id_hash_2(pn, session_id);
+	struct l2tp_session *session;
+	struct hlist_node *walk;
+
+	rcu_read_lock_bh();
+	hlist_for_each_entry_rcu(session, walk, session_list, global_hlist) {
+		if (session->session_id == session_id) {
+			rcu_read_unlock_bh();
+			return session;
+		}
+	}
+	rcu_read_unlock_bh();
+
+	return NULL;
+}
+
+/* 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 *
+l2tp_session_id_hash(struct l2tp_tunnel *tunnel, u32 session_id)
+{
+	return &tunnel->session_hlist[hash_32(session_id, L2TP_HASH_BITS)];
+}
+
+/* Lookup a session by id
+ */
+struct l2tp_session *l2tp_session_find(struct net *net, struct l2tp_tunnel *tunnel, u32 session_id)
+{
+	struct hlist_head *session_list;
+	struct l2tp_session *session;
+	struct hlist_node *walk;
+
+	/* In L2TPv3, session_ids are unique over all tunnels and we
+	 * sometimes need to look them up before we know the
+	 * tunnel.
+	 */
+	if (tunnel == NULL)
+		return l2tp_session_find_2(net, session_id);
+
+	session_list = l2tp_session_id_hash(tunnel, session_id);
+	read_lock_bh(&tunnel->hlist_lock);
+	hlist_for_each_entry(session, walk, session_list, hlist) {
+		if (session->session_id == session_id) {
+			read_unlock_bh(&tunnel->hlist_lock);
+			return session;
+		}
+	}
+	read_unlock_bh(&tunnel->hlist_lock);
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(l2tp_session_find);
+
+struct l2tp_session *l2tp_session_find_nth(struct l2tp_tunnel *tunnel, int nth)
+{
+	int hash;
+	struct hlist_node *walk;
+	struct l2tp_session *session;
+	int count = 0;
+
+	read_lock_bh(&tunnel->hlist_lock);
+	for (hash = 0; hash < L2TP_HASH_SIZE; hash++) {
+		hlist_for_each_entry(session, walk, &tunnel->session_hlist[hash], hlist) {
+			if (++count > nth) {
+				read_unlock_bh(&tunnel->hlist_lock);
+				return session;
+			}
+		}
+	}
+
+	read_unlock_bh(&tunnel->hlist_lock);
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(l2tp_session_find_nth);
+
+/* Lookup a session by interface name.
+ * This is very inefficient but is only used by management interfaces.
+ */
+struct l2tp_session *l2tp_session_find_by_ifname(struct net *net, char *ifname)
+{
+	struct l2tp_net *pn = l2tp_pernet(net);
+	int hash;
+	struct hlist_node *walk;
+	struct l2tp_session *session;
+
+	rcu_read_lock_bh();
+	for (hash = 0; hash < L2TP_HASH_SIZE_2; hash++) {
+		hlist_for_each_entry_rcu(session, walk, &pn->l2tp_session_hlist[hash], global_hlist) {
+			if (!strcmp(session->ifname, ifname)) {
+				rcu_read_unlock_bh();
+				return session;
+			}
+		}
+	}
+
+	rcu_read_unlock_bh();
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(l2tp_session_find_by_ifname);
+
+/* Lookup a tunnel by id
+ */
+struct l2tp_tunnel *l2tp_tunnel_find(struct net *net, u32 tunnel_id)
+{
+	struct l2tp_tunnel *tunnel;
+	struct l2tp_net *pn = l2tp_pernet(net);
+
+	rcu_read_lock_bh();
+	list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {
+		if (tunnel->tunnel_id == tunnel_id) {
+			rcu_read_unlock_bh();
+			return tunnel;
+		}
+	}
+	rcu_read_unlock_bh();
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(l2tp_tunnel_find);
+
+struct l2tp_tunnel *l2tp_tunnel_find_nth(struct net *net, int nth)
+{
+	struct l2tp_net *pn = l2tp_pernet(net);
+	struct l2tp_tunnel *tunnel;
+	int count = 0;
+
+	rcu_read_lock_bh();
+	list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {
+		if (++count > nth) {
+			rcu_read_unlock_bh();
+			return tunnel;
+		}
+	}
+
+	rcu_read_unlock_bh();
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(l2tp_tunnel_find_nth);
+
+/*****************************************************************************
+ * Receive data handling
+ *****************************************************************************/
+
+/* Queue a skb in order. We come here only if the skb has an L2TP sequence
+ * number.
+ */
+static void l2tp_recv_queue_skb(struct l2tp_session *session, struct sk_buff *skb)
+{
+	struct sk_buff *skbp;
+	struct sk_buff *tmp;
+	u32 ns = L2TP_SKB_CB(skb)->ns;
+
+	spin_lock_bh(&session->reorder_q.lock);
+	skb_queue_walk_safe(&session->reorder_q, skbp, tmp) {
+		if (L2TP_SKB_CB(skbp)->ns > ns) {
+			__skb_queue_before(&session->reorder_q, skbp, skb);
+			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
+			       "%s: pkt %hu, inserted before %hu, reorder_q len=%d\n",
+			       session->name, ns, L2TP_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_bh(&session->reorder_q.lock);
+}
+
+/* Dequeue a single skb.
+ */
+static void l2tp_recv_dequeue_skb(struct l2tp_session *session, struct sk_buff *skb)
+{
+	struct l2tp_tunnel *tunnel = session->tunnel;
+	int length = L2TP_SKB_CB(skb)->length;
+
+	/* We're about to requeue the skb, so return resources
+	 * to its current owner (a socket receive buffer).
+	 */
+	skb_orphan(skb);
+
+	tunnel->stats.rx_packets++;
+	tunnel->stats.rx_bytes += length;
+	session->stats.rx_packets++;
+	session->stats.rx_bytes += length;
+
+	if (L2TP_SKB_CB(skb)->has_seq) {
+		/* Bump our Nr */
+		session->nr++;
+		if (tunnel->version == L2TP_HDR_VER_2)
+			session->nr &= 0xffff;
+		else
+			session->nr &= 0xffffff;
+
+		PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
+		       "%s: updated nr to %hu\n", session->name, session->nr);
+	}
+
+	/* call private receive handler */
+	if (session->recv_skb != NULL)
+		(*session->recv_skb)(session, skb, L2TP_SKB_CB(skb)->length);
+	else
+		kfree_skb(skb);
+
+	if (session->deref)
+		(*session->deref)(session);
+}
+
+/* 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 l2tp_recv_dequeue(struct l2tp_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.
+	 */
+start:
+	spin_lock_bh(&session->reorder_q.lock);
+	skb_queue_walk_safe(&session->reorder_q, skb, tmp) {
+		if (time_after(jiffies, L2TP_SKB_CB(skb)->expires)) {
+			session->stats.rx_seq_discards++;
+			session->stats.rx_errors++;
+			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
+			       "%s: oos pkt %u len %d discarded (too old), "
+			       "waiting for %u, reorder_q_len=%d\n",
+			       session->name, L2TP_SKB_CB(skb)->ns,
+			       L2TP_SKB_CB(skb)->length, session->nr,
+			       skb_queue_len(&session->reorder_q));
+			__skb_unlink(skb, &session->reorder_q);
+			kfree_skb(skb);
+			if (session->deref)
+				(*session->deref)(session);
+			continue;
+		}
+
+		if (L2TP_SKB_CB(skb)->has_seq) {
+			if (L2TP_SKB_CB(skb)->ns != session->nr) {
+				PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
+				       "%s: holding oos pkt %u len %d, "
+				       "waiting for %u, reorder_q_len=%d\n",
+				       session->name, L2TP_SKB_CB(skb)->ns,
+				       L2TP_SKB_CB(skb)->length, session->nr,
+				       skb_queue_len(&session->reorder_q));
+				goto out;
+			}
+		}
+		__skb_unlink(skb, &session->reorder_q);
+
+		/* Process the skb. We release the queue lock while we
+		 * do so to let other contexts process the queue.
+		 */
+		spin_unlock_bh(&session->reorder_q.lock);
+		l2tp_recv_dequeue_skb(session, skb);
+		goto start;
+	}
+
+out:
+	spin_unlock_bh(&session->reorder_q.lock);
+}
+
+static inline int l2tp_verify_udp_checksum(struct sock *sk,
+					   struct sk_buff *skb)
+{
+	struct udphdr *uh = udp_hdr(skb);
+	u16 ulen = ntohs(uh->len);
+	struct inet_sock *inet;
+	__wsum psum;
+
+	if (sk->sk_no_check || skb_csum_unnecessary(skb) || !uh->check)
+		return 0;
+
+	inet = inet_sk(sk);
+	psum = csum_tcpudp_nofold(inet->inet_saddr, inet->inet_daddr, ulen,
+				  IPPROTO_UDP, 0);
+
+	if ((skb->ip_summed == CHECKSUM_COMPLETE) &&
+	    !csum_fold(csum_add(psum, skb->csum)))
+		return 0;
+
+	skb->csum = psum;
+
+	return __skb_checksum_complete(skb);
+}
+
+/* Do receive processing of L2TP data frames. We handle both L2TPv2
+ * and L2TPv3 data frames here.
+ *
+ * L2TPv2 Data Message Header
+ *
+ *  0                   1                   2                   3
+ *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |T|L|x|x|S|x|O|P|x|x|x|x|  Ver  |          Length (opt)         |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |           Tunnel ID           |           Session ID          |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |             Ns (opt)          |             Nr (opt)          |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |      Offset Size (opt)        |    Offset pad... (opt)
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ * Data frames are marked by T=0. All other fields are the same as
+ * those in L2TP control frames.
+ *
+ * L2TPv3 Data Message Header
+ *
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |                      L2TP Session Header                      |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |                      L2-Specific Sublayer                     |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |                        Tunnel Payload                      ...
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ * L2TPv3 Session Header Over IP
+ *
+ *  0                   1                   2                   3
+ *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |                           Session ID                          |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |               Cookie (optional, maximum 64 bits)...
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *                                                                 |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ * L2TPv3 L2-Specific Sublayer Format
+ *
+ *  0                   1                   2                   3
+ *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |x|S|x|x|x|x|x|x|              Sequence Number                  |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ * Cookie value, sublayer format and offset (pad) are negotiated with
+ * the peer when the session is set up. Unlike L2TPv2, we do not need
+ * to parse the packet header to determine if optional fields are
+ * present.
+ *
+ * Caller must already have parsed the frame and determined that it is
+ * a data (not control) frame before coming here. Fields up to the
+ * session-id have already been parsed and ptr points to the data
+ * after the session-id.
+ */
+void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
+		      unsigned char *ptr, unsigned char *optr, u16 hdrflags,
+		      int length, int (*payload_hook)(struct sk_buff *skb))
+{
+	struct l2tp_tunnel *tunnel = session->tunnel;
+	int offset;
+	u32 ns, nr;
+
+	/* The ref count is increased since we now hold a pointer to
+	 * the session. Take care to decrement the refcnt when exiting
+	 * this function from now on...
+	 */
+	l2tp_session_inc_refcount(session);
+	if (session->ref)
+		(*session->ref)(session);
+
+	/* Parse and check optional cookie */
+	if (session->peer_cookie_len > 0) {
+		if (memcmp(ptr, &session->peer_cookie[0], session->peer_cookie_len)) {
+			PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_INFO,
+			       "%s: cookie mismatch (%u/%u). Discarding.\n",
+			       tunnel->name, tunnel->tunnel_id, session->session_id);
+			session->stats.rx_cookie_discards++;
+			goto discard;
+		}
+		ptr += session->peer_cookie_len;
+	}
+
+	/* Handle the optional sequence numbers. Sequence numbers are
+	 * in different places for L2TPv2 and L2TPv3.
+	 *
+	 * 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.
+	 */
+	ns = nr = 0;
+	L2TP_SKB_CB(skb)->has_seq = 0;
+	if (tunnel->version == L2TP_HDR_VER_2) {
+		if (hdrflags & L2TP_HDRFLAG_S) {
+			ns = ntohs(*(__be16 *) ptr);
+			ptr += 2;
+			nr = ntohs(*(__be16 *) ptr);
+			ptr += 2;
+
+			/* Store L2TP info in the skb */
+			L2TP_SKB_CB(skb)->ns = ns;
+			L2TP_SKB_CB(skb)->has_seq = 1;
+
+			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
+			       "%s: recv data ns=%u, nr=%u, session nr=%u\n",
+			       session->name, ns, nr, session->nr);
+		}
+	} else if (session->l2specific_type == L2TP_L2SPECTYPE_DEFAULT) {
+		u32 l2h = ntohl(*(__be32 *) ptr);
+
+		if (l2h & 0x40000000) {
+			ns = l2h & 0x00ffffff;
+
+			/* Store L2TP info in the skb */
+			L2TP_SKB_CB(skb)->ns = ns;
+			L2TP_SKB_CB(skb)->has_seq = 1;
+
+			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
+			       "%s: recv data ns=%u, session nr=%u\n",
+			       session->name, ns, session->nr);
+		}
+	}
+
+	/* Advance past L2-specific header, if present */
+	ptr += session->l2specific_len;
+
+	if (L2TP_SKB_CB(skb)->has_seq) {
+		/* 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, L2TP_MSG_SEQ, KERN_INFO,
+			       "%s: requested to enable seq numbers by LNS\n",
+			       session->name);
+			session->send_seq = -1;
+			l2tp_session_set_header_len(session, tunnel->version);
+		}
+	} else {
+		/* No sequence numbers.
+		 * If user has configured mandatory sequence numbers, discard.
+		 */
+		if (session->recv_seq) {
+			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_WARNING,
+			       "%s: recv data has no seq numbers when required. "
+			       "Discarding\n", session->name);
+			session->stats.rx_seq_discards++;
+			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, L2TP_MSG_SEQ, KERN_INFO,
+			       "%s: requested to disable seq numbers by LNS\n",
+			       session->name);
+			session->send_seq = 0;
+			l2tp_session_set_header_len(session, tunnel->version);
+		} else if (session->send_seq) {
+			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_WARNING,
+			       "%s: recv data has no seq numbers when required. "
+			       "Discarding\n", session->name);
+			session->stats.rx_seq_discards++;
+			goto discard;
+		}
+	}
+
+	/* Session data offset is handled differently for L2TPv2 and
+	 * L2TPv3. For L2TPv2, there is an optional 16-bit value in
+	 * the header. For L2TPv3, the offset is negotiated using AVPs
+	 * in the session setup control protocol.
+	 */
+	if (tunnel->version == L2TP_HDR_VER_2) {
+		/* If offset bit set, skip it. */
+		if (hdrflags & L2TP_HDRFLAG_O) {
+			offset = ntohs(*(__be16 *)ptr);
+			ptr += 2 + offset;
+		}
+	} else
+		ptr += session->offset;
+
+	offset = ptr - optr;
+	if (!pskb_may_pull(skb, offset))
+		goto discard;
+
+	__skb_pull(skb, offset);
+
+	/* If caller wants to process the payload before we queue the
+	 * packet, do so now.
+	 */
+	if (payload_hook)
+		if ((*payload_hook)(skb))
+			goto discard;
+
+	/* Prepare skb for adding to the session's reorder_q.  Hold
+	 * packets for max reorder_timeout or 1 second if not
+	 * reordering.
+	 */
+	L2TP_SKB_CB(skb)->length = length;
+	L2TP_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 (L2TP_SKB_CB(skb)->has_seq) {
+		if (session->reorder_timeout != 0) {
+			/* Packet reordering enabled. Add skb to session's
+			 * reorder queue, in order of ns.
+			 */
+			l2tp_recv_queue_skb(session, skb);
+		} else {
+			/* Packet reordering disabled. Discard out-of-sequence
+			 * packets
+			 */
+			if (L2TP_SKB_CB(skb)->ns != session->nr) {
+				session->stats.rx_seq_discards++;
+				PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
+				       "%s: oos pkt %u len %d discarded, "
+				       "waiting for %u, reorder_q_len=%d\n",
+				       session->name, L2TP_SKB_CB(skb)->ns,
+				       L2TP_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. */
+	l2tp_recv_dequeue(session);
+
+	l2tp_session_dec_refcount(session);
+
+	return;
+
+discard:
+	session->stats.rx_errors++;
+	kfree_skb(skb);
+
+	if (session->deref)
+		(*session->deref)(session);
+
+	l2tp_session_dec_refcount(session);
+}
+EXPORT_SYMBOL(l2tp_recv_common);
+
+/* Internal UDP 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 l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb,
+			      int (*payload_hook)(struct sk_buff *skb))
+{
+	struct l2tp_session *session = NULL;
+	unsigned char *ptr, *optr;
+	u16 hdrflags;
+	u32 tunnel_id, session_id;
+	int offset;
+	u16 version;
+	int length;
+
+	if (tunnel->sock && l2tp_verify_udp_checksum(tunnel->sock, skb))
+		goto discard_bad_csum;
+
+	/* UDP always verifies the packet length. */
+	__skb_pull(skb, sizeof(struct udphdr));
+
+	/* Short packet? */
+	if (!pskb_may_pull(skb, L2TP_HDR_SIZE_SEQ)) {
+		PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_INFO,
+		       "%s: recv short packet (len=%d)\n", tunnel->name, skb->len);
+		goto error;
+	}
+
+	/* Trace packet contents, if enabled */
+	if (tunnel->debug & L2TP_MSG_DATA) {
+		length = min(32u, skb->len);
+		if (!pskb_may_pull(skb, length))
+			goto error;
+
+		printk(KERN_DEBUG "%s: recv: ", tunnel->name);
+
+		offset = 0;
+		do {
+			printk(" %02X", skb->data[offset]);
+		} while (++offset < length);
+
+		printk("\n");
+	}
+
+	/* Point to L2TP header */
+	optr = ptr = skb->data;
+
+	/* Get L2TP header flags */
+	hdrflags = ntohs(*(__be16 *) ptr);
+
+	/* Check protocol version */
+	version = hdrflags & L2TP_HDR_VER_MASK;
+	if (version != tunnel->version) {
+		PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_INFO,
+		       "%s: recv protocol version mismatch: got %d expected %d\n",
+		       tunnel->name, version, tunnel->version);
+		goto error;
+	}
+
+	/* Get length of L2TP packet */
+	length = skb->len;
+
+	/* If type is control packet, it is handled by userspace. */
+	if (hdrflags & L2TP_HDRFLAG_T) {
+		PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_DEBUG,
+		       "%s: recv control packet, len=%d\n", tunnel->name, length);
+		goto error;
+	}
+
+	/* Skip flags */
+	ptr += 2;
+
+	if (tunnel->version == L2TP_HDR_VER_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;
+	} else {
+		ptr += 2;	/* skip reserved bits */
+		tunnel_id = tunnel->tunnel_id;
+		session_id = ntohl(*(__be32 *) ptr);
+		ptr += 4;
+	}
+
+	/* Find the session context */
+	session = l2tp_session_find(tunnel->l2tp_net, tunnel, session_id);
+	if (!session || !session->recv_skb) {
+		/* Not found? Pass to userspace to deal with */
+		PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_INFO,
+		       "%s: no session found (%u/%u). Passing up.\n",
+		       tunnel->name, tunnel_id, session_id);
+		goto error;
+	}
+
+	l2tp_recv_common(session, skb, ptr, optr, hdrflags, length, payload_hook);
+
+	return 0;
+
+discard_bad_csum:
+	LIMIT_NETDEBUG("%s: UDP: bad checksum\n", tunnel->name);
+	UDP_INC_STATS_USER(tunnel->l2tp_net, UDP_MIB_INERRORS, 0);
+	tunnel->stats.rx_errors++;
+	kfree_skb(skb);
+
+	return 0;
+
+error:
+	/* Put UDP header back */
+	__skb_push(skb, sizeof(struct udphdr));
+
+	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.
+ */
+int l2tp_udp_encap_recv(struct sock *sk, struct sk_buff *skb)
+{
+	struct l2tp_tunnel *tunnel;
+
+	tunnel = l2tp_sock_to_tunnel(sk);
+	if (tunnel == NULL)
+		goto pass_up;
+
+	PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_DEBUG,
+	       "%s: received %d bytes\n", tunnel->name, skb->len);
+
+	if (l2tp_udp_recv_core(tunnel, skb, tunnel->recv_payload_hook))
+		goto pass_up_put;
+
+	sock_put(sk);
+	return 0;
+
+pass_up_put:
+	sock_put(sk);
+pass_up:
+	return 1;
+}
+EXPORT_SYMBOL_GPL(l2tp_udp_encap_recv);
+
+/************************************************************************
+ * Transmit handling
+ ***********************************************************************/
+
+/* Build an L2TP header for the session into the buffer provided.
+ */
+static int l2tp_build_l2tpv2_header(struct l2tp_session *session, void *buf)
+{
+	struct l2tp_tunnel *tunnel = session->tunnel;
+	__be16 *bufp = buf;
+	__be16 *optr = buf;
+	u16 flags = L2TP_HDR_VER_2;
+	u32 tunnel_id = tunnel->peer_tunnel_id;
+	u32 session_id = session->peer_session_id;
+
+	if (session->send_seq)
+		flags |= L2TP_HDRFLAG_S;
+
+	/* Setup L2TP header. */
+	*bufp++ = htons(flags);
+	*bufp++ = htons(tunnel_id);
+	*bufp++ = htons(session_id);
+	if (session->send_seq) {
+		*bufp++ = htons(session->ns);
+		*bufp++ = 0;
+		session->ns++;
+		session->ns &= 0xffff;
+		PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
+		       "%s: updated ns to %u\n", session->name, session->ns);
+	}
+
+	return bufp - optr;
+}
+
+static int l2tp_build_l2tpv3_header(struct l2tp_session *session, void *buf)
+{
+	struct l2tp_tunnel *tunnel = session->tunnel;
+	char *bufp = buf;
+	char *optr = bufp;
+
+	/* Setup L2TP header. The header differs slightly for UDP and
+	 * IP encapsulations. For UDP, there is 4 bytes of flags.
+	 */
+	if (tunnel->encap == L2TP_ENCAPTYPE_UDP) {
+		u16 flags = L2TP_HDR_VER_3;
+		*((__be16 *) bufp) = htons(flags);
+		bufp += 2;
+		*((__be16 *) bufp) = 0;
+		bufp += 2;
+	}
+
+	*((__be32 *) bufp) = htonl(session->peer_session_id);
+	bufp += 4;
+	if (session->cookie_len) {
+		memcpy(bufp, &session->cookie[0], session->cookie_len);
+		bufp += session->cookie_len;
+	}
+	if (session->l2specific_len) {
+		if (session->l2specific_type == L2TP_L2SPECTYPE_DEFAULT) {
+			u32 l2h = 0;
+			if (session->send_seq) {
+				l2h = 0x40000000 | session->ns;
+				session->ns++;
+				session->ns &= 0xffffff;
+				PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
+				       "%s: updated ns to %u\n", session->name, session->ns);
+			}
+
+			*((__be32 *) bufp) = htonl(l2h);
+		}
+		bufp += session->l2specific_len;
+	}
+	if (session->offset)
+		bufp += session->offset;
+
+	return bufp - optr;
+}
+
+static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb,
+			  struct flowi *fl, size_t data_len)
+{
+	struct l2tp_tunnel *tunnel = session->tunnel;
+	unsigned int len = skb->len;
+	int error;
+
+	/* Debug */
+	if (session->send_seq)
+		PRINTK(session->debug, L2TP_MSG_DATA, KERN_DEBUG,
+		       "%s: send %Zd bytes, ns=%u\n", session->name,
+		       data_len, session->ns - 1);
+	else
+		PRINTK(session->debug, L2TP_MSG_DATA, KERN_DEBUG,
+		       "%s: send %Zd bytes\n", session->name, data_len);
+
+	if (session->debug & L2TP_MSG_DATA) {
+		int i;
+		int uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
+		unsigned char *datap = skb->data + uhlen;
+
+		printk(KERN_DEBUG "%s: xmit:", session->name);
+		for (i = 0; i < (len - uhlen); i++) {
+			printk(" %02X", *datap++);
+			if (i == 31) {
+				printk(" ...");
+				break;
+			}
+		}
+		printk("\n");
+	}
+
+	/* Queue the packet to IP for output */
+	skb->local_df = 1;
+	error = ip_queue_xmit(skb, fl);
+
+	/* Update stats */
+	if (error >= 0) {
+		tunnel->stats.tx_packets++;
+		tunnel->stats.tx_bytes += len;
+		session->stats.tx_packets++;
+		session->stats.tx_bytes += len;
+	} else {
+		tunnel->stats.tx_errors++;
+		session->stats.tx_errors++;
+	}
+
+	return 0;
+}
+
+/* Automatically called when the skb is freed.
+ */
+static void l2tp_sock_wfree(struct sk_buff *skb)
+{
+	sock_put(skb->sk);
+}
+
+/* For data skbs that we transmit, we associate with the tunnel socket
+ * but don't do accounting.
+ */
+static inline void l2tp_skb_set_owner_w(struct sk_buff *skb, struct sock *sk)
+{
+	sock_hold(sk);
+	skb->sk = sk;
+	skb->destructor = l2tp_sock_wfree;
+}
+
+/* If caller requires the skb to have a ppp header, the header must be
+ * inserted in the skb data before calling this function.
+ */
+int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len)
+{
+	int data_len = skb->len;
+	struct l2tp_tunnel *tunnel = session->tunnel;
+	struct sock *sk = tunnel->sock;
+	struct flowi *fl;
+	struct udphdr *uh;
+	struct inet_sock *inet;
+	__wsum csum;
+	int old_headroom;
+	int new_headroom;
+	int headroom;
+	int uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
+	int udp_len;
+
+	/* Check that there's enough headroom in the skb to insert IP,
+	 * UDP and L2TP headers. If not enough, expand it to
+	 * make room. Adjust truesize.
+	 */
+	headroom = NET_SKB_PAD + sizeof(struct iphdr) +
+		uhlen + hdr_len;
+	old_headroom = skb_headroom(skb);
+	if (skb_cow_head(skb, headroom)) {
+		dev_kfree_skb(skb);
+		goto abort;
+	}
+
+	new_headroom = skb_headroom(skb);
+	skb_orphan(skb);
+	skb->truesize += new_headroom - old_headroom;
+
+	/* Setup L2TP header */
+	session->build_header(session, __skb_push(skb, hdr_len));
+
+	/* Reset skb netfilter state */
+	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
+	IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED |
+			      IPSKB_REROUTED);
+	nf_reset(skb);
+
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
+		dev_kfree_skb(skb);
+		goto out_unlock;
+	}
+
+	/* Get routing info from the tunnel socket */
+	skb_dst_drop(skb);
+	skb_dst_set(skb, dst_clone(__sk_dst_check(sk, 0)));
+
+	inet = inet_sk(sk);
+	fl = &inet->cork.fl;
+	switch (tunnel->encap) {
+	case L2TP_ENCAPTYPE_UDP:
+		/* Setup UDP header */
+		__skb_push(skb, sizeof(*uh));
+		skb_reset_transport_header(skb);
+		uh = udp_hdr(skb);
+		uh->source = inet->inet_sport;
+		uh->dest = inet->inet_dport;
+		udp_len = uhlen + hdr_len + data_len;
+		uh->len = htons(udp_len);
+		uh->check = 0;
+
+		/* Calculate UDP checksum if configured to do so */
+		if (sk->sk_no_check == UDP_CSUM_NOXMIT)
+			skb->ip_summed = CHECKSUM_NONE;
+		else if ((skb_dst(skb) && skb_dst(skb)->dev) &&
+			 (!(skb_dst(skb)->dev->features & NETIF_F_V4_CSUM))) {
+			skb->ip_summed = CHECKSUM_COMPLETE;
+			csum = skb_checksum(skb, 0, udp_len, 0);
+			uh->check = csum_tcpudp_magic(inet->inet_saddr,
+						      inet->inet_daddr,
+						      udp_len, IPPROTO_UDP, csum);
+			if (uh->check == 0)
+				uh->check = CSUM_MANGLED_0;
+		} else {
+			skb->ip_summed = CHECKSUM_PARTIAL;
+			skb->csum_start = skb_transport_header(skb) - skb->head;
+			skb->csum_offset = offsetof(struct udphdr, check);
+			uh->check = ~csum_tcpudp_magic(inet->inet_saddr,
+						       inet->inet_daddr,
+						       udp_len, IPPROTO_UDP, 0);
+		}
+		break;
+
+	case L2TP_ENCAPTYPE_IP:
+		break;
+	}
+
+	l2tp_skb_set_owner_w(skb, sk);
+
+	l2tp_xmit_core(session, skb, fl, data_len);
+out_unlock:
+	bh_unlock_sock(sk);
+
+abort:
+	return 0;
+}
+EXPORT_SYMBOL_GPL(l2tp_xmit_skb);
+
+/*****************************************************************************
+ * Tinnel and session create/destroy.
+ *****************************************************************************/
+
+/* Tunnel socket destruct hook.
+ * The tunnel context is deleted only when all session sockets have been
+ * closed.
+ */
+static void l2tp_tunnel_destruct(struct sock *sk)
+{
+	struct l2tp_tunnel *tunnel;
+
+	tunnel = sk->sk_user_data;
+	if (tunnel == NULL)
+		goto end;
+
+	PRINTK(tunnel->debug, L2TP_MSG_CONTROL, KERN_INFO,
+	       "%s: closing...\n", tunnel->name);
+
+	/* Close all sessions */
+	l2tp_tunnel_closeall(tunnel);
+
+	switch (tunnel->encap) {
+	case L2TP_ENCAPTYPE_UDP:
+		/* No longer an encapsulation socket. See net/ipv4/udp.c */
+		(udp_sk(sk))->encap_type = 0;
+		(udp_sk(sk))->encap_rcv = NULL;
+		break;
+	case L2TP_ENCAPTYPE_IP:
+		break;
+	}
+
+	/* Remove hooks into tunnel socket */
+	tunnel->sock = NULL;
+	sk->sk_destruct = tunnel->old_sk_destruct;
+	sk->sk_user_data = NULL;
+
+	/* Call the original destructor */
+	if (sk->sk_destruct)
+		(*sk->sk_destruct)(sk);
+
+	/* We're finished with the socket */
+	l2tp_tunnel_dec_refcount(tunnel);
+
+end:
+	return;
+}
+
+/* When the tunnel is closed, all the attached sessions need to go too.
+ */
+static void l2tp_tunnel_closeall(struct l2tp_tunnel *tunnel)
+{
+	int hash;
+	struct hlist_node *walk;
+	struct hlist_node *tmp;
+	struct l2tp_session *session;
+
+	BUG_ON(tunnel == NULL);
+
+	PRINTK(tunnel->debug, L2TP_MSG_CONTROL, KERN_INFO,
+	       "%s: closing all sessions...\n", tunnel->name);
+
+	write_lock_bh(&tunnel->hlist_lock);
+	for (hash = 0; hash < L2TP_HASH_SIZE; hash++) {
+again:
+		hlist_for_each_safe(walk, tmp, &tunnel->session_hlist[hash]) {
+			session = hlist_entry(walk, struct l2tp_session, hlist);
+
+			PRINTK(session->debug, L2TP_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.
+			 */
+			if (session->ref != NULL)
+				(*session->ref)(session);
+
+			write_unlock_bh(&tunnel->hlist_lock);
+
+			if (tunnel->version != L2TP_HDR_VER_2) {
+				struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);
+
+				spin_lock_bh(&pn->l2tp_session_hlist_lock);
+				hlist_del_init_rcu(&session->global_hlist);
+				spin_unlock_bh(&pn->l2tp_session_hlist_lock);
+				synchronize_rcu();
+			}
+
+			if (session->session_close != NULL)
+				(*session->session_close)(session);
+
+			if (session->deref != NULL)
+				(*session->deref)(session);
+
+			write_lock_bh(&tunnel->hlist_lock);
+
+			/* 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.
+			 */
+			goto again;
+		}
+	}
+	write_unlock_bh(&tunnel->hlist_lock);
+}
+
+/* Really kill the tunnel.
+ * Come here only when all sessions have been cleared from the tunnel.
+ */
+static void l2tp_tunnel_free(struct l2tp_tunnel *tunnel)
+{
+	struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);
+
+	BUG_ON(atomic_read(&tunnel->ref_count) != 0);
+	BUG_ON(tunnel->sock != NULL);
+
+	PRINTK(tunnel->debug, L2TP_MSG_CONTROL, KERN_INFO,
+	       "%s: free...\n", tunnel->name);
+
+	/* Remove from tunnel list */
+	spin_lock_bh(&pn->l2tp_tunnel_list_lock);
+	list_del_rcu(&tunnel->list);
+	spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
+	synchronize_rcu();
+
+	atomic_dec(&l2tp_tunnel_count);
+	kfree(tunnel);
+}
+
+/* Create a socket for the tunnel, if one isn't set up by
+ * userspace. This is used for static tunnels where there is no
+ * managing L2TP daemon.
+ */
+static int l2tp_tunnel_sock_create(u32 tunnel_id, u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg, struct socket **sockp)
+{
+	int err = -EINVAL;
+	struct sockaddr_in udp_addr;
+	struct sockaddr_l2tpip ip_addr;
+	struct socket *sock = NULL;
+
+	switch (cfg->encap) {
+	case L2TP_ENCAPTYPE_UDP:
+		err = sock_create(AF_INET, SOCK_DGRAM, 0, sockp);
+		if (err < 0)
+			goto out;
+
+		sock = *sockp;
+
+		memset(&udp_addr, 0, sizeof(udp_addr));
+		udp_addr.sin_family = AF_INET;
+		udp_addr.sin_addr = cfg->local_ip;
+		udp_addr.sin_port = htons(cfg->local_udp_port);
+		err = kernel_bind(sock, (struct sockaddr *) &udp_addr, sizeof(udp_addr));
+		if (err < 0)
+			goto out;
+
+		udp_addr.sin_family = AF_INET;
+		udp_addr.sin_addr = cfg->peer_ip;
+		udp_addr.sin_port = htons(cfg->peer_udp_port);
+		err = kernel_connect(sock, (struct sockaddr *) &udp_addr, sizeof(udp_addr), 0);
+		if (err < 0)
+			goto out;
+
+		if (!cfg->use_udp_checksums)
+			sock->sk->sk_no_check = UDP_CSUM_NOXMIT;
+
+		break;
+
+	case L2TP_ENCAPTYPE_IP:
+		err = sock_create(AF_INET, SOCK_DGRAM, IPPROTO_L2TP, sockp);
+		if (err < 0)
+			goto out;
+
+		sock = *sockp;
+
+		memset(&ip_addr, 0, sizeof(ip_addr));
+		ip_addr.l2tp_family = AF_INET;
+		ip_addr.l2tp_addr = cfg->local_ip;
+		ip_addr.l2tp_conn_id = tunnel_id;
+		err = kernel_bind(sock, (struct sockaddr *) &ip_addr, sizeof(ip_addr));
+		if (err < 0)
+			goto out;
+
+		ip_addr.l2tp_family = AF_INET;
+		ip_addr.l2tp_addr = cfg->peer_ip;
+		ip_addr.l2tp_conn_id = peer_tunnel_id;
+		err = kernel_connect(sock, (struct sockaddr *) &ip_addr, sizeof(ip_addr), 0);
+		if (err < 0)
+			goto out;
+
+		break;
+
+	default:
+		goto out;
+	}
+
+out:
+	if ((err < 0) && sock) {
+		sock_release(sock);
+		*sockp = NULL;
+	}
+
+	return err;
+}
+
+int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg, struct l2tp_tunnel **tunnelp)
+{
+	struct l2tp_tunnel *tunnel = NULL;
+	int err;
+	struct socket *sock = NULL;
+	struct sock *sk = NULL;
+	struct l2tp_net *pn;
+	enum l2tp_encap_type encap = L2TP_ENCAPTYPE_UDP;
+
+	/* Get the tunnel socket from the fd, which was opened by
+	 * the userspace L2TP daemon. If not specified, create a
+	 * kernel socket.
+	 */
+	if (fd < 0) {
+		err = l2tp_tunnel_sock_create(tunnel_id, peer_tunnel_id, cfg, &sock);
+		if (err < 0)
+			goto err;
+	} else {
+		err = -EBADF;
+		sock = sockfd_lookup(fd, &err);
+		if (!sock) {
+			printk(KERN_ERR "tunl %hu: sockfd_lookup(fd=%d) returned %d\n",
+			       tunnel_id, fd, err);
+			goto err;
+		}
+	}
+
+	sk = sock->sk;
+
+	if (cfg != NULL)
+		encap = cfg->encap;
+
+	/* Quick sanity checks */
+	switch (encap) {
+	case L2TP_ENCAPTYPE_UDP:
+		err = -EPROTONOSUPPORT;
+		if (sk->sk_protocol != IPPROTO_UDP) {
+			printk(KERN_ERR "tunl %hu: fd %d wrong protocol, got %d, expected %d\n",
+			       tunnel_id, fd, sk->sk_protocol, IPPROTO_UDP);
+			goto err;
+		}
+		break;
+	case L2TP_ENCAPTYPE_IP:
+		err = -EPROTONOSUPPORT;
+		if (sk->sk_protocol != IPPROTO_L2TP) {
+			printk(KERN_ERR "tunl %hu: fd %d wrong protocol, got %d, expected %d\n",
+			       tunnel_id, fd, sk->sk_protocol, IPPROTO_L2TP);
+			goto err;
+		}
+		break;
+	}
+
+	/* Check if this socket has already been prepped */
+	tunnel = (struct l2tp_tunnel *)sk->sk_user_data;
+	if (tunnel != NULL) {
+		/* This socket has already been prepped */
+		err = -EBUSY;
+		goto err;
+	}
+
+	tunnel = kzalloc(sizeof(struct l2tp_tunnel), GFP_KERNEL);
+	if (tunnel == NULL) {
+		err = -ENOMEM;
+		goto err;
+	}
+
+	tunnel->version = version;
+	tunnel->tunnel_id = tunnel_id;
+	tunnel->peer_tunnel_id = peer_tunnel_id;
+	tunnel->debug = L2TP_DEFAULT_DEBUG_FLAGS;
+
+	tunnel->magic = L2TP_TUNNEL_MAGIC;
+	sprintf(&tunnel->name[0], "tunl %u", tunnel_id);
+	rwlock_init(&tunnel->hlist_lock);
+
+	/* The net we belong to */
+	tunnel->l2tp_net = net;
+	pn = l2tp_pernet(net);
+
+	if (cfg != NULL)
+		tunnel->debug = cfg->debug;
+
+	/* Mark socket as an encapsulation socket. See net/ipv4/udp.c */
+	tunnel->encap = encap;
+	if (encap == L2TP_ENCAPTYPE_UDP) {
+		/* Mark socket as an encapsulation socket. See net/ipv4/udp.c */
+		udp_sk(sk)->encap_type = UDP_ENCAP_L2TPINUDP;
+		udp_sk(sk)->encap_rcv = l2tp_udp_encap_recv;
+	}
+
+	sk->sk_user_data = tunnel;
+
+	/* 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 = &l2tp_tunnel_destruct;
+	tunnel->sock = sk;
+	sk->sk_allocation = GFP_ATOMIC;
+
+	/* Add tunnel to our list */
+	INIT_LIST_HEAD(&tunnel->list);
+	atomic_inc(&l2tp_tunnel_count);
+
+	/* Bump the reference count. The tunnel context is deleted
+	 * only when this drops to zero. Must be done before list insertion
+	 */
+	l2tp_tunnel_inc_refcount(tunnel);
+	spin_lock_bh(&pn->l2tp_tunnel_list_lock);
+	list_add_rcu(&tunnel->list, &pn->l2tp_tunnel_list);
+	spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
+
+	err = 0;
+err:
+	if (tunnelp)
+		*tunnelp = tunnel;
+
+	/* If tunnel's socket was created by the kernel, it doesn't
+	 *  have a file.
+	 */
+	if (sock && sock->file)
+		sockfd_put(sock);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(l2tp_tunnel_create);
+
+/* This function is used by the netlink TUNNEL_DELETE command.
+ */
+int l2tp_tunnel_delete(struct l2tp_tunnel *tunnel)
+{
+	int err = 0;
+	struct socket *sock = tunnel->sock ? tunnel->sock->sk_socket : NULL;
+
+	/* Force the tunnel socket to close. This will eventually
+	 * cause the tunnel to be deleted via the normal socket close
+	 * mechanisms when userspace closes the tunnel socket.
+	 */
+	if (sock != NULL) {
+		err = inet_shutdown(sock, 2);
+
+		/* If the tunnel's socket was created by the kernel,
+		 * close the socket here since the socket was not
+		 * created by userspace.
+		 */
+		if (sock->file == NULL)
+			err = inet_release(sock);
+	}
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(l2tp_tunnel_delete);
+
+/* Really kill the session.
+ */
+void l2tp_session_free(struct l2tp_session *session)
+{
+	struct l2tp_tunnel *tunnel;
+
+	BUG_ON(atomic_read(&session->ref_count) != 0);
+
+	tunnel = session->tunnel;
+	if (tunnel != NULL) {
+		BUG_ON(tunnel->magic != L2TP_TUNNEL_MAGIC);
+
+		/* Delete the session from the hash */
+		write_lock_bh(&tunnel->hlist_lock);
+		hlist_del_init(&session->hlist);
+		write_unlock_bh(&tunnel->hlist_lock);
+
+		/* Unlink from the global hash if not L2TPv2 */
+		if (tunnel->version != L2TP_HDR_VER_2) {
+			struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);
+
+			spin_lock_bh(&pn->l2tp_session_hlist_lock);
+			hlist_del_init_rcu(&session->global_hlist);
+			spin_unlock_bh(&pn->l2tp_session_hlist_lock);
+			synchronize_rcu();
+		}
+
+		if (session->session_id != 0)
+			atomic_dec(&l2tp_session_count);
+
+		sock_put(tunnel->sock);
+
+		/* This will delete the tunnel context if this
+		 * is the last session on the tunnel.
+		 */
+		session->tunnel = NULL;
+		l2tp_tunnel_dec_refcount(tunnel);
+	}
+
+	kfree(session);
+
+	return;
+}
+EXPORT_SYMBOL_GPL(l2tp_session_free);
+
+/* This function is used by the netlink SESSION_DELETE command and by
+   pseudowire modules.
+ */
+int l2tp_session_delete(struct l2tp_session *session)
+{
+	if (session->session_close != NULL)
+		(*session->session_close)(session);
+
+	l2tp_session_dec_refcount(session);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(l2tp_session_delete);
+
+
+/* We come here whenever a session's send_seq, cookie_len or
+ * l2specific_len parameters are set.
+ */
+static void l2tp_session_set_header_len(struct l2tp_session *session, int version)
+{
+	if (version == L2TP_HDR_VER_2) {
+		session->hdr_len = 6;
+		if (session->send_seq)
+			session->hdr_len += 4;
+	} else {
+		session->hdr_len = 4 + session->cookie_len + session->l2specific_len + session->offset;
+		if (session->tunnel->encap == L2TP_ENCAPTYPE_UDP)
+			session->hdr_len += 4;
+	}
+
+}
+
+struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunnel, u32 session_id, u32 peer_session_id, struct l2tp_session_cfg *cfg)
+{
+	struct l2tp_session *session;
+
+	session = kzalloc(sizeof(struct l2tp_session) + priv_size, GFP_KERNEL);
+	if (session != NULL) {
+		session->magic = L2TP_SESSION_MAGIC;
+		session->tunnel = tunnel;
+
+		session->session_id = session_id;
+		session->peer_session_id = peer_session_id;
+		session->nr = 1;
+
+		sprintf(&session->name[0], "sess %u/%u",
+			tunnel->tunnel_id, session->session_id);
+
+		skb_queue_head_init(&session->reorder_q);
+
+		INIT_HLIST_NODE(&session->hlist);
+		INIT_HLIST_NODE(&session->global_hlist);
+
+		/* Inherit debug options from tunnel */
+		session->debug = tunnel->debug;
+
+		if (cfg) {
+			session->pwtype = cfg->pw_type;
+			session->debug = cfg->debug;
+			session->mtu = cfg->mtu;
+			session->mru = cfg->mru;
+			session->send_seq = cfg->send_seq;
+			session->recv_seq = cfg->recv_seq;
+			session->lns_mode = cfg->lns_mode;
+			session->reorder_timeout = cfg->reorder_timeout;
+			session->offset = cfg->offset;
+			session->l2specific_type = cfg->l2specific_type;
+			session->l2specific_len = cfg->l2specific_len;
+			session->cookie_len = cfg->cookie_len;
+			memcpy(&session->cookie[0], &cfg->cookie[0], cfg->cookie_len);
+			session->peer_cookie_len = cfg->peer_cookie_len;
+			memcpy(&session->peer_cookie[0], &cfg->peer_cookie[0], cfg->peer_cookie_len);
+		}
+
+		if (tunnel->version == L2TP_HDR_VER_2)
+			session->build_header = l2tp_build_l2tpv2_header;
+		else
+			session->build_header = l2tp_build_l2tpv3_header;
+
+		l2tp_session_set_header_len(session, tunnel->version);
+
+		/* Bump the reference count. The session context is deleted
+		 * only when this drops to zero.
+		 */
+		l2tp_session_inc_refcount(session);
+		l2tp_tunnel_inc_refcount(tunnel);
+
+		/* Ensure tunnel socket isn't deleted */
+		sock_hold(tunnel->sock);
+
+		/* Add session to the tunnel's hash list */
+		write_lock_bh(&tunnel->hlist_lock);
+		hlist_add_head(&session->hlist,
+			       l2tp_session_id_hash(tunnel, session_id));
+		write_unlock_bh(&tunnel->hlist_lock);
+
+		/* And to the global session list if L2TPv3 */
+		if (tunnel->version != L2TP_HDR_VER_2) {
+			struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);
+
+			spin_lock_bh(&pn->l2tp_session_hlist_lock);
+			hlist_add_head_rcu(&session->global_hlist,
+					   l2tp_session_id_hash_2(pn, session_id));
+			spin_unlock_bh(&pn->l2tp_session_hlist_lock);
+		}
+
+		/* Ignore management session in session count value */
+		if (session->session_id != 0)
+			atomic_inc(&l2tp_session_count);
+	}
+
+	return session;
+}
+EXPORT_SYMBOL_GPL(l2tp_session_create);
+
+/*****************************************************************************
+ * Init and cleanup
+ *****************************************************************************/
+
+static __net_init int l2tp_init_net(struct net *net)
+{
+	struct l2tp_net *pn = net_generic(net, l2tp_net_id);
+	int hash;
+
+	INIT_LIST_HEAD(&pn->l2tp_tunnel_list);
+	spin_lock_init(&pn->l2tp_tunnel_list_lock);
+
+	for (hash = 0; hash < L2TP_HASH_SIZE_2; hash++)
+		INIT_HLIST_HEAD(&pn->l2tp_session_hlist[hash]);
+
+	spin_lock_init(&pn->l2tp_session_hlist_lock);
+
+	return 0;
+}
+
+static struct pernet_operations l2tp_net_ops = {
+	.init = l2tp_init_net,
+	.id   = &l2tp_net_id,
+	.size = sizeof(struct l2tp_net),
+};
+
+static int __init l2tp_init(void)
+{
+	int rc = 0;
+
+	rc = register_pernet_device(&l2tp_net_ops);
+	if (rc)
+		goto out;
+
+	printk(KERN_INFO "L2TP core driver, %s\n", L2TP_DRV_VERSION);
+
+out:
+	return rc;
+}
+
+static void __exit l2tp_exit(void)
+{
+	unregister_pernet_device(&l2tp_net_ops);
+}
+
+module_init(l2tp_init);
+module_exit(l2tp_exit);
+
+MODULE_AUTHOR("James Chapman <jchapman@katalix.com>");
+MODULE_DESCRIPTION("L2TP core");
+MODULE_LICENSE("GPL");
+MODULE_VERSION(L2TP_DRV_VERSION);
+