l2tp_core.c 46.1 KB
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/*
 * 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>
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#include <linux/rculist.h>
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#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>
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#include <linux/in.h>
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#include <linux/ip.h>
#include <linux/udp.h>
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#include <linux/l2tp.h>
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#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>
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#include <net/inet_common.h>
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#include <net/xfrm.h>
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#include <net/protocol.h>
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#include <asm/byteorder.h>
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#include <linux/atomic.h>
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#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
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#define L2TP_HDR_VER_3	   0x0003
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/* 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 {
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	u32			ns;
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	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;
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	spinlock_t l2tp_tunnel_list_lock;
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	struct hlist_head l2tp_session_hlist[L2TP_HASH_SIZE_2];
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	spinlock_t l2tp_session_hlist_lock;
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};

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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);

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static inline struct l2tp_net *l2tp_pernet(struct net *net)
{
	BUG_ON(!net);

	return net_generic(net, l2tp_net_id);
}

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/* 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

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/* 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;

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	rcu_read_lock_bh();
	hlist_for_each_entry_rcu(session, walk, session_list, global_hlist) {
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		if (session->session_id == session_id) {
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			rcu_read_unlock_bh();
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			return session;
		}
	}
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	rcu_read_unlock_bh();
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	return NULL;
}

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/* 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
 */
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struct l2tp_session *l2tp_session_find(struct net *net, struct l2tp_tunnel *tunnel, u32 session_id)
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{
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	struct hlist_head *session_list;
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	struct l2tp_session *session;
	struct hlist_node *walk;

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	/* 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);
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	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);

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/* 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;

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	rcu_read_lock_bh();
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	for (hash = 0; hash < L2TP_HASH_SIZE_2; hash++) {
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		hlist_for_each_entry_rcu(session, walk, &pn->l2tp_session_hlist[hash], global_hlist) {
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			if (!strcmp(session->ifname, ifname)) {
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				rcu_read_unlock_bh();
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				return session;
			}
		}
	}

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	rcu_read_unlock_bh();
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	return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_session_find_by_ifname);

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/* 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);

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	rcu_read_lock_bh();
	list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {
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		if (tunnel->tunnel_id == tunnel_id) {
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			rcu_read_unlock_bh();
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			return tunnel;
		}
	}
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	rcu_read_unlock_bh();
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	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;

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	rcu_read_lock_bh();
	list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {
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		if (++count > nth) {
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			rcu_read_unlock_bh();
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			return tunnel;
		}
	}

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	rcu_read_unlock_bh();
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	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;
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	u32 ns = L2TP_SKB_CB(skb)->ns;
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	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++;
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		if (tunnel->version == L2TP_HDR_VER_2)
			session->nr &= 0xffff;
		else
			session->nr &= 0xffffff;

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		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,
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			       "%s: oos pkt %u len %d discarded (too old), "
			       "waiting for %u, reorder_q_len=%d\n",
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			       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,
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				       "%s: holding oos pkt %u len %d, "
				       "waiting for %u, reorder_q_len=%d\n",
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				       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);
}

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/* 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.
526
 */
527
528
529
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))
530
{
531
	struct l2tp_tunnel *tunnel = session->tunnel;
532
	int offset;
533
	u32 ns, nr;
534
535
536
537
538
539
540
541
542

	/* 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);

543
544
545
546
547
548
549
550
551
552
553
554
	/* 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;
	}

555
556
557
558
559
560
561
562
563
	/* 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;
564
565
566
567
568
569
	if (tunnel->version == L2TP_HDR_VER_2) {
		if (hdrflags & L2TP_HDRFLAG_S) {
			ns = ntohs(*(__be16 *) ptr);
			ptr += 2;
			nr = ntohs(*(__be16 *) ptr);
			ptr += 2;
570

571
572
573
			/* Store L2TP info in the skb */
			L2TP_SKB_CB(skb)->ns = ns;
			L2TP_SKB_CB(skb)->has_seq = 1;
574

575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
			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);
		}
593
594
	}

595
596
597
	/* Advance past L2-specific header, if present */
	ptr += session->l2specific_len;

598
599
600
601
602
603
604
605
606
607
	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;
608
			l2tp_session_set_header_len(session, tunnel->version);
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
		}
	} 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;
632
			l2tp_session_set_header_len(session, tunnel->version);
633
634
635
636
637
638
639
640
641
		} 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;
		}
	}

642
643
644
645
646
647
648
649
650
651
652
653
654
	/* 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;
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692

	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,
693
694
				       "%s: oos pkt %u len %d discarded, "
				       "waiting for %u, reorder_q_len=%d\n",
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
				       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);

715
	return;
716
717
718
719
720
721
722
723
724

discard:
	session->stats.rx_errors++;
	kfree_skb(skb);

	if (session->deref)
		(*session->deref)(session);

	l2tp_session_dec_refcount(session);
725
726
727
728
729
730
731
732
733
}
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.
 */
734
735
static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb,
			      int (*payload_hook)(struct sk_buff *skb))
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
{
	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;
	}

	/* 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 (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);
821
	if (!session || !session->recv_skb) {
822
823
824
825
826
827
828
829
		/* 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);
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883

	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.
 */
884
static int l2tp_build_l2tpv2_header(struct l2tp_session *session, void *buf)
885
{
886
	struct l2tp_tunnel *tunnel = session->tunnel;
887
	__be16 *bufp = buf;
888
	__be16 *optr = buf;
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
	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++;
904
		session->ns &= 0xffff;
905
		PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
906
		       "%s: updated ns to %u\n", session->name, session->ns);
907
	}
908
909

	return bufp - optr;
910
911
}

912
static int l2tp_build_l2tpv3_header(struct l2tp_session *session, void *buf)
913
{
914
	struct l2tp_tunnel *tunnel = session->tunnel;
915
916
917
	char *bufp = buf;
	char *optr = bufp;

918
919
920
921
922
923
924
925
926
927
928
	/* 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;
	}

929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
	*((__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;
952

953
	return bufp - optr;
954
955
}

956
static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb,
957
			  struct flowi *fl, size_t data_len)
958
959
960
961
962
963
964
965
{
	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,
966
		       "%s: send %Zd bytes, ns=%u\n", session->name,
967
968
969
970
971
972
973
		       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;
974
975
		int uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
		unsigned char *datap = skb->data + uhlen;
976
977

		printk(KERN_DEBUG "%s: xmit:", session->name);
978
		for (i = 0; i < (len - uhlen); i++) {
979
980
981
982
983
984
985
986
987
988
			printk(" %02X", *datap++);
			if (i == 31) {
				printk(" ...");
				break;
			}
		}
		printk("\n");
	}

	/* Queue the packet to IP for output */
989
	skb->local_df = 1;
990
	error = ip_queue_xmit(skb, fl);
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028

	/* 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;
1029
1030
	struct l2tp_tunnel *tunnel = session->tunnel;
	struct sock *sk = tunnel->sock;
1031
	struct flowi *fl;
1032
1033
1034
1035
1036
1037
	struct udphdr *uh;
	struct inet_sock *inet;
	__wsum csum;
	int old_headroom;
	int new_headroom;
	int headroom;
1038
1039
	int uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
	int udp_len;
1040
1041
1042
1043
1044
1045

	/* 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) +
1046
		uhlen + hdr_len;
1047
	old_headroom = skb_headroom(skb);
1048
1049
	if (skb_cow_head(skb, headroom)) {
		dev_kfree_skb(skb);
1050
		goto abort;
1051
	}
1052
1053
1054
1055
1056
1057

	new_headroom = skb_headroom(skb);
	skb_orphan(skb);
	skb->truesize += new_headroom - old_headroom;

	/* Setup L2TP header */
1058
	session->build_header(session, __skb_push(skb, hdr_len));
1059

1060
	/* Reset skb netfilter state */
1061
1062
1063
1064
1065
	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
	IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED |
			      IPSKB_REROUTED);
	nf_reset(skb);

1066
1067
1068
1069
1070
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	bh_lock_sock(sk);
	if (sock_owned_by_user(sk)) {
		dev_kfree_skb(skb);
		goto out_unlock;
	}

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	/* Get routing info from the tunnel socket */
	skb_dst_drop(skb);
	skb_dst_set(skb, dst_clone(__sk_dst_get(sk)));

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	inet = inet_sk(sk);
	fl = &inet->cork.fl;
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	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;
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	}

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	l2tp_skb_set_owner_w(skb, sk);

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	l2tp_xmit_core(session, skb, fl, data_len);
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out_unlock:
	bh_unlock_sock(sk);
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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.
 */
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static void l2tp_tunnel_destruct(struct sock *sk)
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{
	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);

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	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;
	}
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	/* 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.
 */
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static void l2tp_tunnel_closeall(struct l2tp_tunnel *tunnel)
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{
	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);

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			if (tunnel->version != L2TP_HDR_VER_2) {
				struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);

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				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();
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			}

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			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.
 */
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static void l2tp_tunnel_free(struct l2tp_tunnel *tunnel)
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{
	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 */
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	spin_lock_bh(&pn->l2tp_tunnel_list_lock);
	list_del_rcu(&tunnel->list);
	spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
	synchronize_rcu();
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	atomic_dec(&l2tp_tunnel_count);
	kfree(tunnel);
}

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/* 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;
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	struct socket *sock = NULL;
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	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;
}

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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;
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	enum l2tp_encap_type encap = L2TP_ENCAPTYPE_UDP;
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	/* Get the tunnel socket from the fd, which was opened by
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	 * the userspace L2TP daemon. If not specified, create a
	 * kernel socket.
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	 */
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	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;
		}
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	}

	sk = sock->sk;

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	if (cfg != NULL)
		encap = cfg->encap;

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	/* Quick sanity checks */
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	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;
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	}

	/* 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);

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	if (cfg != NULL)
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		tunnel->debug = cfg->debug;

	/* Mark socket as an encapsulation socket. See net/ipv4/udp.c */
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	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;
	}
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	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
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	 * only when this drops to zero. Must be done before list insertion
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	 */
	l2tp_tunnel_inc_refcount(tunnel);
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	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);
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	err = 0;
err:
	if (tunnelp)
		*tunnelp = tunnel;

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	/* If tunnel's socket was created by the kernel, it doesn't
	 *  have a file.
	 */
	if (sock && sock->file)
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		sockfd_put(sock);

	return err;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_create);

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/* This function is used by the netlink TUNNEL_DELETE command.
 */
int l2tp_tunnel_delete(struct l2tp_tunnel *tunnel)
{
	int err = 0;
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	struct socket *sock = tunnel->sock ? tunnel->sock->sk_socket : NULL;
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	/* 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.
	 */
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	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);
	}
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	return err;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_delete);

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/* 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);

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		/* Unlink from the global hash if not L2TPv2 */
		if (tunnel->version != L2TP_HDR_VER_2) {
			struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);

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			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();
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		}

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		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);

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/* 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);


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/* We come here whenever a session's send_seq, cookie_len or
 * l2specific_len parameters are set.
 */
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static void l2tp_session_set_header_len(struct l2tp_session *session, int version)
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{
	if (version == L2TP_HDR_VER_2) {
		session->hdr_len = 6;
		if (session->send_seq)
			session->hdr_len += 4;
	} else {
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		session->hdr_len = 4 + session->cookie_len + session->l2specific_len + session->offset;
		if (session->tunnel->encap == L2TP_ENCAPTYPE_UDP)
			session->hdr_len += 4;
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	}

}

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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;
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		session->nr = 1;
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		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);
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		INIT_HLIST_NODE(&session->global_hlist);
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		/* Inherit debug options from tunnel */
		session->debug = tunnel->debug;

		if (cfg) {
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			session->pwtype = cfg->pw_type;
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			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;
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			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);
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		}

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		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);

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		/* 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);

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		/* And to the global session list if L2TPv3 */
		if (tunnel->version != L2TP_HDR_VER_2) {
			struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);

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			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);
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		}

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		/* 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)
{
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	struct l2tp_net *pn = net_generic(net, l2tp_net_id);
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	int hash;
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	INIT_LIST_HEAD(&pn->l2tp_tunnel_list);
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	spin_lock_init(&pn->l2tp_tunnel_list_lock);
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	for (hash = 0; hash < L2TP_HASH_SIZE_2; hash++)
		INIT_HLIST_HEAD(&pn->l2tp_session_hlist[hash]);

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	spin_lock_init(&pn->l2tp_session_hlist_lock);
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	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);