l2tp: Split pppol2tp patch into separate l2tp and ppp parts

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

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

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

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

1 files changed, 1227 insertions, 0 deletions

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
new file mode 100644
index 000000000000..4b6da3689893
--- /dev/null
+++ b/net/l2tp/l2tp_core.c
@@ -0,0 +1,1227 @@
+/*
+ * 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/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/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/xfrm.h>
+
+#include <asm/byteorder.h>
+#include <asm/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
+
+/* 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 {
+	u16			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;
+	rwlock_t l2tp_tunnel_list_lock;
+};
+
+static inline struct l2tp_net *l2tp_pernet(struct net *net)
+{
+	BUG_ON(!net);
+
+	return net_generic(net, l2tp_net_id);
+}
+
+/* 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 l2tp_tunnel *tunnel, u32 session_id)
+{
+	struct hlist_head *session_list =
+		l2tp_session_id_hash(tunnel, session_id);
+	struct l2tp_session *session;
+	struct hlist_node *walk;
+
+	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 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);
+
+	read_lock_bh(&pn->l2tp_tunnel_list_lock);
+	list_for_each_entry(tunnel, &pn->l2tp_tunnel_list, list) {
+		if (tunnel->tunnel_id == tunnel_id) {
+			read_unlock_bh(&pn->l2tp_tunnel_list_lock);
+			return tunnel;
+		}
+	}
+	read_unlock_bh(&pn->l2tp_tunnel_list_lock);
+
+	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;
+
+	read_lock_bh(&pn->l2tp_tunnel_list_lock);
+	list_for_each_entry(tunnel, &pn->l2tp_tunnel_list, list) {
+		if (++count > nth) {
+			read_unlock_bh(&pn->l2tp_tunnel_list_lock);
+			return tunnel;
+		}
+	}
+
+	read_unlock_bh(&pn->l2tp_tunnel_list_lock);
+
+	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;
+	u16 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++;
+		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.
+	 */
+	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 %hu len %d discarded (too old), "
+			       "waiting for %hu, 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 %hu len %d, "
+				       "waiting for %hu, 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);
+		spin_lock_bh(&session->reorder_q.lock);
+	}
+
+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);
+}
+
+/* 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.
+ */
+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 length;
+	int offset;
+	u16 version;
+	u16 ns, nr;
+
+	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;
+	}
+
+	/* Point to L2TP header */
+	optr = ptr = skb->data;
+
+	/* 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", ptr[offset]);
+		} while (++offset < length);
+
+		printk("\n");
+	}
+
+	/* 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 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 = l2tp_session_find(tunnel, session_id);
+	if (!session) {
+		/* Not found? Pass to userspace to deal with */
+		PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_INFO,
+		       "%s: no session found (%hu/%hu). Passing up.\n",
+		       tunnel->name, tunnel_id, session_id);
+		goto error;
+	}
+
+	/* 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);
+
+	/* 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 (hdrflags & L2TP_HDRFLAG_S) {
+		ns = (u16) 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=%hu, nr=%hu, session nr=%hu\n",
+		       session->name, ns, nr, session->nr);
+	}
+
+	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;
+		}
+	} 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;
+		} 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;
+		}
+	}
+
+	/* If offset bit set, skip it. */
+	if (hdrflags & L2TP_HDRFLAG_O) {
+		offset = ntohs(*(__be16 *)ptr);
+		ptr += 2 + 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 %hu len %d discarded, "
+				       "waiting for %hu, 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 0;
+
+discard:
+	session->stats.rx_errors++;
+	kfree_skb(skb);
+
+	if (session->deref)
+		(*session->deref)(session);
+
+	l2tp_session_dec_refcount(session);
+
+	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;
+}
+EXPORT_SYMBOL_GPL(l2tp_udp_recv_core);
+
+/* 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 void l2tp_build_l2tpv2_header(struct l2tp_tunnel *tunnel,
+				     struct l2tp_session *session,
+				     void *buf)
+{
+	__be16 *bufp = 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++;
+		PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
+		       "%s: updated ns to %hu\n", session->name, session->ns);
+	}
+}
+
+void l2tp_build_l2tp_header(struct l2tp_session *session, void *buf)
+{
+	struct l2tp_tunnel *tunnel = session->tunnel;
+
+	BUG_ON(tunnel->version != L2TP_HDR_VER_2);
+	l2tp_build_l2tpv2_header(tunnel, session, buf);
+}
+EXPORT_SYMBOL_GPL(l2tp_build_l2tp_header);
+
+int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb, 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=%hu\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;
+		unsigned char *datap = skb->data + sizeof(struct udphdr);
+
+		printk(KERN_DEBUG "%s: xmit:", session->name);
+		for (i = 0; i < (len - sizeof(struct udphdr)); i++) {
+			printk(" %02X", *datap++);
+			if (i == 31) {
+				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 += len;
+		session->stats.tx_packets++;
+		session->stats.tx_bytes += len;
+	} else {
+		tunnel->stats.tx_errors++;
+		session->stats.tx_errors++;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(l2tp_xmit_core);
+
+/* 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 sock *sk = session->tunnel->sock;
+	struct udphdr *uh;
+	unsigned int udp_len;
+	struct inet_sock *inet;
+	__wsum csum;
+	int old_headroom;
+	int new_headroom;
+	int headroom;
+
+	/* 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) +
+		sizeof(struct udphdr) + hdr_len;
+	old_headroom = skb_headroom(skb);
+	if (skb_cow_head(skb, headroom))
+		goto abort;
+
+	new_headroom = skb_headroom(skb);
+	skb_orphan(skb);
+	skb->truesize += new_headroom - old_headroom;
+
+	/* Setup L2TP header */
+	l2tp_build_l2tp_header(session, __skb_push(skb, hdr_len));
+	udp_len = sizeof(struct udphdr) + hdr_len + data_len;
+
+	/* Setup UDP header */
+	inet = inet_sk(sk);
+	__skb_push(skb, sizeof(*uh));
+	skb_reset_transport_header(skb);
+	uh = udp_hdr(skb);
+	uh->source = inet->inet_sport;
+	uh->dest = inet->inet_dport;
+	uh->len = htons(udp_len);
+
+	uh->check = 0;
+
+	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
+	IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED |
+			      IPSKB_REROUTED);
+	nf_reset(skb);
+
+	/* Get routing info from the tunnel socket */
+	skb_dst_drop(skb);
+	skb_dst_set(skb, dst_clone(__sk_dst_get(sk)));
+	l2tp_skb_set_owner_w(skb, sk);
+
+	/* 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);
+	}
+
+	l2tp_xmit_core(session, skb, data_len);
+
+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.
+ */
+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);
+
+	/* 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 the original destructor */
+	if (sk->sk_destruct)
+		(*sk->sk_destruct)(sk);
+
+	/* We're finished with the socket */
+	l2tp_tunnel_dec_refcount(tunnel);
+
+end:
+	return;
+}
+EXPORT_SYMBOL(l2tp_tunnel_destruct);
+
+/* When the tunnel is closed, all the attached sessions need to go too.
+ */
+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 (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);
+}
+EXPORT_SYMBOL_GPL(l2tp_tunnel_closeall);
+
+/* Really kill the tunnel.
+ * Come here only when all sessions have been cleared from the tunnel.
+ */
+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 */
+	write_lock_bh(&pn->l2tp_tunnel_list_lock);
+	list_del_init(&tunnel->list);
+	write_unlock_bh(&pn->l2tp_tunnel_list_lock);
+
+	atomic_dec(&l2tp_tunnel_count);
+	kfree(tunnel);
+}
+EXPORT_SYMBOL_GPL(l2tp_tunnel_free);
+
+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;
+
+	/* Get the tunnel socket from the fd, which was opened by
+	 * the userspace L2TP daemon.
+	 */
+	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;
+
+	/* Quick sanity checks */
+	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;
+	}
+	err = -EAFNOSUPPORT;
+	if (sock->ops->family != AF_INET) {
+		printk(KERN_ERR "tunl %hu: fd %d wrong family, got %d, expected %d\n",
+		       tunnel_id, fd, sock->ops->family, AF_INET);
+		goto err;
+	}
+
+	/* 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;
+	}
+
+	if (version != L2TP_HDR_VER_2)
+		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)
+		tunnel->debug = cfg->debug;
+
+	/* 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);
+	write_lock_bh(&pn->l2tp_tunnel_list_lock);
+	list_add(&tunnel->list, &pn->l2tp_tunnel_list);
+	write_unlock_bh(&pn->l2tp_tunnel_list_lock);
+	atomic_inc(&l2tp_tunnel_count);
+
+	/* Bump the reference count. The tunnel context is deleted
+	 * only when this drops to zero.
+	 */
+	l2tp_tunnel_inc_refcount(tunnel);
+
+	err = 0;
+err:
+	if (tunnelp)
+		*tunnelp = tunnel;
+
+	if (sock)
+		sockfd_put(sock);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(l2tp_tunnel_create);
+
+/* 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);
+
+		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);
+
+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;
+
+		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);
+
+		/* Inherit debug options from tunnel */
+		session->debug = tunnel->debug;
+
+		if (cfg) {
+			session->debug = cfg->debug;
+			session->hdr_len = cfg->hdr_len;
+			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;
+		}
+
+		/* 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);
+
+		/* 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;
+	int err;
+
+	pn = kzalloc(sizeof(*pn), GFP_KERNEL);
+	if (!pn)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&pn->l2tp_tunnel_list);
+	rwlock_init(&pn->l2tp_tunnel_list_lock);
+
+	err = net_assign_generic(net, l2tp_net_id, pn);
+	if (err)
+		goto out;
+
+	return 0;
+
+out:
+	kfree(pn);
+	return err;
+}
+
+static __net_exit void l2tp_exit_net(struct net *net)
+{
+	struct l2tp_net *pn;
+
+	pn = net_generic(net, l2tp_net_id);
+	/*
+	 * if someone has cached our net then
+	 * further net_generic call will return NULL
+	 */
+	net_assign_generic(net, l2tp_net_id, NULL);
+	kfree(pn);
+}
+
+static struct pernet_operations l2tp_net_ops = {
+	.init = l2tp_init_net,
+	.exit = l2tp_exit_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);
+