/*
   * 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.
   */

  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

  #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/udp_tunnel.h>

  #include <net/inet_common.h>

  #include <net/xfrm.h>

  #include <net/protocol.h>

  #include <net/inet6_connection_sock.h>
  #include <net/inet_ecn.h>
  #include <net/ip6_route.h>

  #include <net/ip6_checksum.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

  /* 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;

  static struct workqueue_struct *l2tp_wq;

  
  /* 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_tunnel_free(struct l2tp_tunnel *tunnel);

  static inline struct l2tp_tunnel *l2tp_tunnel(struct sock *sk)
  {
  	return sk->sk_user_data;
  }

  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 {									\
  	pr_debug("l2tp_tunnel_inc_refcount: %s:%d %s: cnt=%d
  ",	\
  		 __func__, __LINE__, (_t)->name,			\
  		 atomic_read(&_t->ref_count));				\
  	l2tp_tunnel_inc_refcount_1(_t);					\
  } while (0)

  #define l2tp_tunnel_dec_refcount(_t)					\

  do {									\
  	pr_debug("l2tp_tunnel_dec_refcount: %s:%d %s: cnt=%d
  ",	\
  		 __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 the tunnel socket, possibly involving the fs code if the socket is
   * owned by userspace.  A struct sock returned from this function must be
   * released using l2tp_tunnel_sock_put once you're done with it.
   */

  static struct sock *l2tp_tunnel_sock_lookup(struct l2tp_tunnel *tunnel)

  {
  	int err = 0;
  	struct socket *sock = NULL;
  	struct sock *sk = NULL;
  
  	if (!tunnel)
  		goto out;
  
  	if (tunnel->fd >= 0) {
  		/* Socket is owned by userspace, who might be in the process
  		 * of closing it.  Look the socket up using the fd to ensure
  		 * consistency.
  		 */
  		sock = sockfd_lookup(tunnel->fd, &err);
  		if (sock)
  			sk = sock->sk;
  	} else {
  		/* Socket is owned by kernelspace */
  		sk = tunnel->sock;

  		sock_hold(sk);

  	}
  
  out:
  	return sk;
  }

  
  /* Drop a reference to a tunnel socket obtained via. l2tp_tunnel_sock_put */

  static void l2tp_tunnel_sock_put(struct sock *sk)

  {
  	struct l2tp_tunnel *tunnel = l2tp_sock_to_tunnel(sk);
  	if (tunnel) {
  		if (tunnel->fd >= 0) {
  			/* Socket is owned by userspace */
  			sockfd_put(sk->sk_socket);
  		}
  		sock_put(sk);
  	}

  	sock_put(sk);

  }

  /* 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;

  	rcu_read_lock_bh();

  	hlist_for_each_entry_rcu(session, 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;

  	/* 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, 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 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, &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 l2tp_session *session;

  	rcu_read_lock_bh();

  	for (hash = 0; hash < L2TP_HASH_SIZE_2; hash++) {

  		hlist_for_each_entry_rcu(session, &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);

  			l2tp_dbg(session, L2TP_MSG_SEQ,
  				 "%s: pkt %hu, inserted before %hu, reorder_q len=%d
  ",
  				 session->name, ns, L2TP_SKB_CB(skbp)->ns,
  				 skb_queue_len(&session->reorder_q));

  			atomic_long_inc(&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);

  	atomic_long_inc(&tunnel->stats.rx_packets);
  	atomic_long_add(length, &tunnel->stats.rx_bytes);
  	atomic_long_inc(&session->stats.rx_packets);
  	atomic_long_add(length, &session->stats.rx_bytes);

  
  	if (L2TP_SKB_CB(skb)->has_seq) {
  		/* Bump our Nr */
  		session->nr++;

  		session->nr &= session->nr_max;

  		l2tp_dbg(session, L2TP_MSG_SEQ, "%s: updated nr to %hu
  ",
  			 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)) {

  			atomic_long_inc(&session->stats.rx_seq_discards);
  			atomic_long_inc(&session->stats.rx_errors);

  			l2tp_dbg(session, L2TP_MSG_SEQ,
  				 "%s: oos pkt %u len %d discarded (too old), waiting for %u, reorder_q_len=%d
  ",
  				 session->name, L2TP_SKB_CB(skb)->ns,
  				 L2TP_SKB_CB(skb)->length, session->nr,
  				 skb_queue_len(&session->reorder_q));

  			session->reorder_skip = 1;

  			__skb_unlink(skb, &session->reorder_q);
  			kfree_skb(skb);
  			if (session->deref)
  				(*session->deref)(session);
  			continue;
  		}
  
  		if (L2TP_SKB_CB(skb)->has_seq) {

  			if (session->reorder_skip) {

  				l2tp_dbg(session, L2TP_MSG_SEQ,
  					 "%s: advancing nr to next pkt: %u -> %u",
  					 session->name, session->nr,
  					 L2TP_SKB_CB(skb)->ns);

  				session->reorder_skip = 0;
  				session->nr = L2TP_SKB_CB(skb)->ns;
  			}

  			if (L2TP_SKB_CB(skb)->ns != session->nr) {

  				l2tp_dbg(session, L2TP_MSG_SEQ,
  					 "%s: holding oos pkt %u len %d, waiting for %u, reorder_q_len=%d
  ",
  					 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 int l2tp_seq_check_rx_window(struct l2tp_session *session, u32 nr)
  {
  	u32 nws;
  
  	if (nr >= session->nr)
  		nws = nr - session->nr;
  	else
  		nws = (session->nr_max + 1) - (session->nr - nr);
  
  	return nws < session->nr_window_size;
  }

  /* If packet has sequence numbers, queue it if acceptable. Returns 0 if
   * acceptable, else non-zero.
   */
  static int l2tp_recv_data_seq(struct l2tp_session *session, struct sk_buff *skb)
  {

  	if (!l2tp_seq_check_rx_window(session, L2TP_SKB_CB(skb)->ns)) {
  		/* Packet sequence number is outside allowed window.
  		 * Discard it.
  		 */
  		l2tp_dbg(session, L2TP_MSG_SEQ,
  			 "%s: pkt %u len %d discarded, outside window, nr=%u
  ",
  			 session->name, L2TP_SKB_CB(skb)->ns,
  			 L2TP_SKB_CB(skb)->length, session->nr);
  		goto discard;
  	}

  	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);

  		goto out;
  	}
  
  	/* Packet reordering disabled. Discard out-of-sequence packets, while
  	 * tracking the number if in-sequence packets after the first OOS packet
  	 * is seen. After nr_oos_count_max in-sequence packets, reset the
  	 * sequence number to re-enable packet reception.
  	 */
  	if (L2TP_SKB_CB(skb)->ns == session->nr) {
  		skb_queue_tail(&session->reorder_q, skb);

  	} else {

  		u32 nr_oos = L2TP_SKB_CB(skb)->ns;
  		u32 nr_next = (session->nr_oos + 1) & session->nr_max;
  
  		if (nr_oos == nr_next)
  			session->nr_oos_count++;
  		else
  			session->nr_oos_count = 0;
  
  		session->nr_oos = nr_oos;
  		if (session->nr_oos_count > session->nr_oos_count_max) {
  			session->reorder_skip = 1;
  			l2tp_dbg(session, L2TP_MSG_SEQ,
  				 "%s: %d oos packets received. Resetting sequence numbers
  ",
  				 session->name, session->nr_oos_count);
  		}
  		if (!session->reorder_skip) {

  			atomic_long_inc(&session->stats.rx_seq_discards);
  			l2tp_dbg(session, L2TP_MSG_SEQ,
  				 "%s: oos pkt %u len %d discarded, waiting for %u, reorder_q_len=%d
  ",
  				 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);
  	}

  out:

  	return 0;
  
  discard:
  	return 1;
  }

  /* 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)) {

  			l2tp_info(tunnel, L2TP_MSG_DATA,
  				  "%s: cookie mismatch (%u/%u). Discarding.
  ",
  				  tunnel->name, tunnel->tunnel_id,
  				  session->session_id);

  			atomic_long_inc(&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;

  			l2tp_dbg(session, L2TP_MSG_SEQ,
  				 "%s: recv data ns=%u, nr=%u, session nr=%u
  ",
  				 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;

  			l2tp_dbg(session, L2TP_MSG_SEQ,
  				 "%s: recv data ns=%u, session nr=%u
  ",
  				 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)) {

  			l2tp_info(session, L2TP_MSG_SEQ,
  				  "%s: requested to enable seq numbers by LNS
  ",
  				  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) {

  			l2tp_warn(session, L2TP_MSG_SEQ,
  				  "%s: recv data has no seq numbers when required. Discarding.
  ",
  				  session->name);

  			atomic_long_inc(&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)) {

  			l2tp_info(session, L2TP_MSG_SEQ,
  				  "%s: requested to disable seq numbers by LNS
  ",
  				  session->name);

  			session->send_seq = 0;

  			l2tp_session_set_header_len(session, tunnel->version);

  		} else if (session->send_seq) {

  			l2tp_warn(session, L2TP_MSG_SEQ,
  				  "%s: recv data has no seq numbers when required. Discarding.
  ",
  				  session->name);

  			atomic_long_inc(&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 (l2tp_recv_data_seq(session, skb))
  			goto discard;

  	} 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:

  	atomic_long_inc(&session->stats.rx_errors);

  	kfree_skb(skb);
  
  	if (session->deref)
  		(*session->deref)(session);
  
  	l2tp_session_dec_refcount(session);

  }
  EXPORT_SYMBOL(l2tp_recv_common);

  /* Drop skbs from the session's reorder_q
   */
  int l2tp_session_queue_purge(struct l2tp_session *session)
  {
  	struct sk_buff *skb = NULL;
  	BUG_ON(!session);
  	BUG_ON(session->magic != L2TP_SESSION_MAGIC);
  	while ((skb = skb_dequeue(&session->reorder_q))) {
  		atomic_long_inc(&session->stats.rx_errors);
  		kfree_skb(skb);
  		if (session->deref)
  			(*session->deref)(session);
  	}
  	return 0;
  }
  EXPORT_SYMBOL_GPL(l2tp_session_queue_purge);

  /* 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;

  	u16 version;
  	int length;

  	/* UDP has verifed checksum */

  
  	/* UDP always verifies the packet length. */
  	__skb_pull(skb, sizeof(struct udphdr));
  
  	/* Short packet? */
  	if (!pskb_may_pull(skb, L2TP_HDR_SIZE_SEQ)) {

  		l2tp_info(tunnel, L2TP_MSG_DATA,
  			  "%s: recv short packet (len=%d)
  ",
  			  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;

  		pr_debug("%s: recv
  ", tunnel->name);
  		print_hex_dump_bytes("", DUMP_PREFIX_OFFSET, skb->data, length);

  	}

  	/* 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) {

  		l2tp_info(tunnel, L2TP_MSG_DATA,
  			  "%s: recv protocol version mismatch: got %d expected %d
  ",
  			  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) {

  		l2tp_dbg(tunnel, L2TP_MSG_DATA,
  			 "%s: recv control packet, len=%d
  ",
  			 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 */

  		l2tp_info(tunnel, L2TP_MSG_DATA,
  			  "%s: no session found (%u/%u). Passing up.
  ",
  			  tunnel->name, tunnel_id, session_id);

  		goto error;
  	}
  
  	l2tp_recv_common(session, skb, ptr, optr, hdrflags, length, payload_hook);

  
  	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;

  	l2tp_dbg(tunnel, L2TP_MSG_DATA, "%s: received %d bytes
  ",
  		 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;

  		l2tp_dbg(session, L2TP_MSG_SEQ, "%s: updated ns to %u
  ",
  			 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;

  				l2tp_dbg(session, L2TP_MSG_SEQ,
  					 "%s: updated ns to %u
  ",
  					 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)

  		l2tp_dbg(session, L2TP_MSG_DATA, "%s: send %Zd bytes, ns=%u
  ",
  			 session->name, data_len, session->ns - 1);

  	else

  		l2tp_dbg(session, L2TP_MSG_DATA, "%s: send %Zd bytes
  ",
  			 session->name, data_len);

  
  	if (session->debug & L2TP_MSG_DATA) {

  		int uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
  		unsigned char *datap = skb->data + uhlen;

  		pr_debug("%s: xmit
  ", session->name);
  		print_hex_dump_bytes("", DUMP_PREFIX_OFFSET,
  				     datap, min_t(size_t, 32, len - uhlen));

  	}
  
  	/* Queue the packet to IP for output */

  	skb->ignore_df = 1;

  #if IS_ENABLED(CONFIG_IPV6)

  	if (tunnel->sock->sk_family == PF_INET6 && !tunnel->v4mapped)

  		error = inet6_csk_xmit(tunnel->sock, skb, NULL);

  	else
  #endif

  		error = ip_queue_xmit(tunnel->sock, skb, fl);

  
  	/* Update stats */
  	if (error >= 0) {

  		atomic_long_inc(&tunnel->stats.tx_packets);
  		atomic_long_add(len, &tunnel->stats.tx_bytes);
  		atomic_long_inc(&session->stats.tx_packets);
  		atomic_long_add(len, &session->stats.tx_bytes);

  	} else {

  		atomic_long_inc(&tunnel->stats.tx_errors);
  		atomic_long_inc(&session->stats.tx_errors);

  	}
  
  	return 0;
  }

  /* 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;

  	int headroom;

  	int uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
  	int udp_len;

  	int ret = NET_XMIT_SUCCESS;

  
  	/* 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;

  	if (skb_cow_head(skb, headroom)) {

  		kfree_skb(skb);
  		return NET_XMIT_DROP;

  	}

  	/* 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)) {

  		kfree_skb(skb);
  		ret = NET_XMIT_DROP;

  		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);

  
  		/* Calculate UDP checksum if configured to do so */

  #if IS_ENABLED(CONFIG_IPV6)

  		if (sk->sk_family == PF_INET6 && !tunnel->v4mapped)

  			udp6_set_csum(udp_get_no_check6_tx(sk),
  				      skb, &inet6_sk(sk)->saddr,
  				      &sk->sk_v6_daddr, udp_len);

  		else
  #endif

  		udp_set_csum(sk->sk_no_check_tx, skb, inet->inet_saddr,
  			     inet->inet_daddr, udp_len);

  		break;
  
  	case L2TP_ENCAPTYPE_IP:
  		break;

  	}

  	l2tp_xmit_core(session, skb, fl, data_len);

  out_unlock:
  	bh_unlock_sock(sk);

  	return ret;

  }
  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 = l2tp_tunnel(sk);

  	struct l2tp_net *pn;

  	if (tunnel == NULL)
  		goto end;

  	l2tp_info(tunnel, L2TP_MSG_CONTROL, "%s: closing...
  ", tunnel->name);

  	/* Disable udp encapsulation */

  	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;

  		(udp_sk(sk))->encap_destroy = NULL;

  		break;
  	case L2TP_ENCAPTYPE_IP:
  		break;
  	}

  
  	/* Remove hooks into tunnel socket */

  	sk->sk_destruct = tunnel->old_sk_destruct;
  	sk->sk_user_data = NULL;

  	tunnel->sock = NULL;

  	/* Remove the tunnel struct from the tunnel list */
  	pn = l2tp_pernet(tunnel->l2tp_net);
  	spin_lock_bh(&pn->l2tp_tunnel_list_lock);
  	list_del_rcu(&tunnel->list);
  	spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
  	atomic_dec(&l2tp_tunnel_count);

  	l2tp_tunnel_closeall(tunnel);

  	l2tp_tunnel_dec_refcount(tunnel);

  	/* Call the original destructor */
  	if (sk->sk_destruct)
  		(*sk->sk_destruct)(sk);

  end:
  	return;
  }

  
  /* 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);

  	l2tp_info(tunnel, L2TP_MSG_CONTROL, "%s: closing all sessions...
  ",
  		  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);

  			l2tp_info(session, L2TP_MSG_CONTROL,
  				  "%s: closing session
  ", session->name);

  
  			hlist_del_init(&session->hlist);

  			if (session->ref != NULL)
  				(*session->ref)(session);
  
  			write_unlock_bh(&tunnel->hlist_lock);

  			__l2tp_session_unhash(session);

  			l2tp_session_queue_purge(session);

  			if (session->session_close != NULL)
  				(*session->session_close)(session);
  
  			if (session->deref != NULL)
  				(*session->deref)(session);

  			l2tp_session_dec_refcount(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);

  /* Tunnel socket destroy hook for UDP encapsulation */
  static void l2tp_udp_encap_destroy(struct sock *sk)
  {
  	struct l2tp_tunnel *tunnel = l2tp_sock_to_tunnel(sk);
  	if (tunnel) {
  		l2tp_tunnel_closeall(tunnel);
  		sock_put(sk);
  	}
  }

  /* 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)

  {

  	BUG_ON(atomic_read(&tunnel->ref_count) != 0);
  	BUG_ON(tunnel->sock != NULL);

  	l2tp_info(tunnel, L2TP_MSG_CONTROL, "%s: free...
  ", tunnel->name);

  	kfree_rcu(tunnel, rcu);

  }

  /* Workqueue tunnel deletion function */
  static void l2tp_tunnel_del_work(struct work_struct *work)
  {
  	struct l2tp_tunnel *tunnel = NULL;
  	struct socket *sock = NULL;
  	struct sock *sk = NULL;
  
  	tunnel = container_of(work, struct l2tp_tunnel, del_work);
  	sk = l2tp_tunnel_sock_lookup(tunnel);
  	if (!sk)
  		return;
  
  	sock = sk->sk_socket;

  	/* If the tunnel socket was created by userspace, then go through the
  	 * inet layer to shut the socket down, and let userspace close it.
  	 * Otherwise, if we created the socket directly within the kernel, use
  	 * the sk API to release it here.

  	 * In either case the tunnel resources are freed in the socket
  	 * destructor when the tunnel socket goes away.

  	 */

  	if (tunnel->fd >= 0) {
  		if (sock)
  			inet_shutdown(sock, 2);

  	} else {

  		if (sock)
  			kernel_sock_shutdown(sock, SHUT_RDWR);
  		sk_release_kernel(sk);

  	}

  
  	l2tp_tunnel_sock_put(sk);

  }

  /* 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.

   *
   * Since we don't want these sockets to keep a namespace alive by
   * themselves, we drop the socket's namespace refcount after creation.
   * These sockets are freed when the namespace exits using the pernet
   * exit hook.

   */

  static int l2tp_tunnel_sock_create(struct net *net,
  				u32 tunnel_id,
  				u32 peer_tunnel_id,
  				struct l2tp_tunnel_cfg *cfg,
  				struct socket **sockp)

  {
  	int err = -EINVAL;

  	struct socket *sock = NULL;

  	struct udp_port_cfg udp_conf;

  
  	switch (cfg->encap) {
  	case L2TP_ENCAPTYPE_UDP:

  		memset(&udp_conf, 0, sizeof(udp_conf));

  #if IS_ENABLED(CONFIG_IPV6)
  		if (cfg->local_ip6 && cfg->peer_ip6) {

  			udp_conf.family = AF_INET6;
  			memcpy(&udp_conf.local_ip6, cfg->local_ip6,
  			       sizeof(udp_conf.local_ip6));
  			memcpy(&udp_conf.peer_ip6, cfg->peer_ip6,
  			       sizeof(udp_conf.peer_ip6));
  			udp_conf.use_udp6_tx_checksums =
  			    cfg->udp6_zero_tx_checksums;
  			udp_conf.use_udp6_rx_checksums =
  			    cfg->udp6_zero_rx_checksums;

  		} else
  #endif
  		{

  			udp_conf.family = AF_INET;
  			udp_conf.local_ip = cfg->local_ip;
  			udp_conf.peer_ip = cfg->peer_ip;
  			udp_conf.use_udp_checksums = cfg->use_udp_checksums;

  		}

  		udp_conf.local_udp_port = htons(cfg->local_udp_port);
  		udp_conf.peer_udp_port = htons(cfg->peer_udp_port);
  
  		err = udp_sock_create(net, &udp_conf, &sock);
  		if (err < 0)
  			goto out;

  
  		break;
  
  	case L2TP_ENCAPTYPE_IP:

  #if IS_ENABLED(CONFIG_IPV6)
  		if (cfg->local_ip6 && cfg->peer_ip6) {

  			struct sockaddr_l2tpip6 ip6_addr = {0};

  			err = sock_create_kern(AF_INET6, SOCK_DGRAM,
  					  IPPROTO_L2TP, &sock);

  			if (err < 0)
  				goto out;

  			sk_change_net(sock->sk, net);

  			ip6_addr.l2tp_family = AF_INET6;
  			memcpy(&ip6_addr.l2tp_addr, cfg->local_ip6,
  			       sizeof(ip6_addr.l2tp_addr));
  			ip6_addr.l2tp_conn_id = tunnel_id;
  			err = kernel_bind(sock, (struct sockaddr *) &ip6_addr,
  					  sizeof(ip6_addr));
  			if (err < 0)
  				goto out;

  			ip6_addr.l2tp_family = AF_INET6;
  			memcpy(&ip6_addr.l2tp_addr, cfg->peer_ip6,
  			       sizeof(ip6_addr.l2tp_addr));
  			ip6_addr.l2tp_conn_id = peer_tunnel_id;
  			err = kernel_connect(sock,
  					     (struct sockaddr *) &ip6_addr,
  					     sizeof(ip6_addr), 0);
  			if (err < 0)
  				goto out;
  		} else
  #endif
  		{

  			struct sockaddr_l2tpip ip_addr = {0};

  			err = sock_create_kern(AF_INET, SOCK_DGRAM,
  					  IPPROTO_L2TP, &sock);

  			if (err < 0)
  				goto out;

  			sk_change_net(sock->sk, net);

  			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:

  	*sockp = sock;

  	if ((err < 0) && sock) {

  		kernel_sock_shutdown(sock, SHUT_RDWR);
  		sk_release_kernel(sock->sk);

  		*sockp = NULL;
  	}
  
  	return err;
  }

  static struct lock_class_key l2tp_socket_class;

  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(net, tunnel_id, peer_tunnel_id,
  				cfg, &sock);

  		if (err < 0)
  			goto err;
  	} else {

  		sock = sockfd_lookup(fd, &err);
  		if (!sock) {

  			pr_err("tunl %u: sockfd_lookup(fd=%d) returned %d
  ",

  			       tunnel_id, fd, err);

  			err = -EBADF;
  			goto err;
  		}
  
  		/* Reject namespace mismatches */
  		if (!net_eq(sock_net(sock->sk), net)) {
  			pr_err("tunl %u: netns mismatch
  ", tunnel_id);
  			err = -EINVAL;

  			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) {

  			pr_err("tunl %hu: fd %d wrong protocol, got %d, expected %d
  ",

  			       tunnel_id, fd, sk->sk_protocol, IPPROTO_UDP);
  			goto err;
  		}
  		break;
  	case L2TP_ENCAPTYPE_IP:
  		err = -EPROTONOSUPPORT;
  		if (sk->sk_protocol != IPPROTO_L2TP) {

  			pr_err("tunl %hu: fd %d wrong protocol, got %d, expected %d
  ",

  			       tunnel_id, fd, sk->sk_protocol, IPPROTO_L2TP);
  			goto err;
  		}
  		break;

  	}
  
  	/* Check if this socket has already been prepped */

  	tunnel = l2tp_tunnel(sk);

  	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;

  #if IS_ENABLED(CONFIG_IPV6)
  	if (sk->sk_family == PF_INET6) {
  		struct ipv6_pinfo *np = inet6_sk(sk);
  
  		if (ipv6_addr_v4mapped(&np->saddr) &&

  		    ipv6_addr_v4mapped(&sk->sk_v6_daddr)) {

  			struct inet_sock *inet = inet_sk(sk);
  
  			tunnel->v4mapped = true;
  			inet->inet_saddr = np->saddr.s6_addr32[3];

  			inet->inet_rcv_saddr = sk->sk_v6_rcv_saddr.s6_addr32[3];
  			inet->inet_daddr = sk->sk_v6_daddr.s6_addr32[3];

  		} else {
  			tunnel->v4mapped = false;
  		}
  	}
  #endif

  	/* Mark socket as an encapsulation socket. See net/ipv4/udp.c */

  	tunnel->encap = encap;
  	if (encap == L2TP_ENCAPTYPE_UDP) {

  		struct udp_tunnel_sock_cfg udp_cfg;
  
  		udp_cfg.sk_user_data = tunnel;
  		udp_cfg.encap_type = UDP_ENCAP_L2TPINUDP;
  		udp_cfg.encap_rcv = l2tp_udp_encap_recv;
  		udp_cfg.encap_destroy = l2tp_udp_encap_destroy;

  		setup_udp_tunnel_sock(net, sock, &udp_cfg);
  	} else {
  		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;

  	tunnel->fd = fd;

  	lockdep_set_class_and_name(&sk->sk_lock.slock, &l2tp_socket_class, "l2tp_sock");

  	sk->sk_allocation = GFP_ATOMIC;

  	/* Init delete workqueue struct */
  	INIT_WORK(&tunnel->del_work, l2tp_tunnel_del_work);

  	/* 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)
  {

  	l2tp_tunnel_closeall(tunnel);

  	return (false == queue_work(l2tp_wq, &tunnel->del_work));

  }
  EXPORT_SYMBOL_GPL(l2tp_tunnel_delete);

  /* Really kill the session.
   */
  void l2tp_session_free(struct l2tp_session *session)
  {

  	struct l2tp_tunnel *tunnel = session->tunnel;

  
  	BUG_ON(atomic_read(&session->ref_count) != 0);

  	if (tunnel) {

  		BUG_ON(tunnel->magic != L2TP_TUNNEL_MAGIC);

  		if (session->session_id != 0)
  			atomic_dec(&l2tp_session_count);
  		sock_put(tunnel->sock);
  		session->tunnel = NULL;
  		l2tp_tunnel_dec_refcount(tunnel);
  	}
  
  	kfree(session);

  }
  EXPORT_SYMBOL_GPL(l2tp_session_free);
  
  /* Remove an l2tp session from l2tp_core's hash lists.
   * Provides a tidyup interface for pseudowire code which can't just route all
   * shutdown via. l2tp_session_delete and a pseudowire-specific session_close
   * callback.
   */
  void __l2tp_session_unhash(struct l2tp_session *session)
  {
  	struct l2tp_tunnel *tunnel = session->tunnel;

  	/* Remove the session from core hashes */
  	if (tunnel) {
  		/* Remove from the per-tunnel hash */

  		write_lock_bh(&tunnel->hlist_lock);
  		hlist_del_init(&session->hlist);
  		write_unlock_bh(&tunnel->hlist_lock);

  		/* For L2TPv3 we have a per-net hash: remove from there, too */

  		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();

  		}

  	}

  }

  EXPORT_SYMBOL_GPL(__l2tp_session_unhash);

  /* This function is used by the netlink SESSION_DELETE command and by
     pseudowire modules.
   */
  int l2tp_session_delete(struct l2tp_session *session)
  {

  	if (session->ref)
  		(*session->ref)(session);
  	__l2tp_session_unhash(session);

  	l2tp_session_queue_purge(session);

  	if (session->session_close != NULL)
  		(*session->session_close)(session);

  	if (session->deref)

  		(*session->deref)(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.
   */

  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;

  	}
  
  }

  EXPORT_SYMBOL_GPL(l2tp_session_set_header_len);

  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 = 0;

  		if (tunnel->version == L2TP_HDR_VER_2)
  			session->nr_max = 0xffff;
  		else
  			session->nr_max = 0xffffff;
  		session->nr_window_size = session->nr_max / 2;

  		session->nr_oos_count_max = 4;
  
  		/* Use NR of first received packet */
  		session->reorder_skip = 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 __net_exit void l2tp_exit_net(struct net *net)
  {
  	struct l2tp_net *pn = l2tp_pernet(net);
  	struct l2tp_tunnel *tunnel = NULL;
  
  	rcu_read_lock_bh();
  	list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {
  		(void)l2tp_tunnel_delete(tunnel);
  	}
  	rcu_read_unlock_bh();
  }

  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;

  	l2tp_wq = alloc_workqueue("l2tp", WQ_UNBOUND, 0);

  	if (!l2tp_wq) {
  		pr_err("alloc_workqueue failed
  ");
  		rc = -ENOMEM;
  		goto out;
  	}

  	pr_info("L2TP core driver, %s
  ", L2TP_DRV_VERSION);

  
  out:
  	return rc;
  }
  
  static void __exit l2tp_exit(void)
  {
  	unregister_pernet_device(&l2tp_net_ops);

  	if (l2tp_wq) {
  		destroy_workqueue(l2tp_wq);
  		l2tp_wq = NULL;
  	}

  }
  
  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);