// SPDX-License-Identifier: GPL-2.0-only
/*
 * 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)
 */

#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_MAX               14

/* 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 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;
};

#if IS_ENABLED(CONFIG_IPV6)
static bool l2tp_sk_is_v6(struct sock *sk)
{
        return sk->sk_family == PF_INET6 &&
               !ipv6_addr_v4mapped(&sk->sk_v6_daddr);
}
#endif

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

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

        return net_generic(net, l2tp_net_id);
}

/* 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)];

}

/* 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)];
}

void l2tp_tunnel_free(struct l2tp_tunnel *tunnel)
{
        sock_put(tunnel->sock);
        /* the tunnel is freed in the socket destructor */
}
EXPORT_SYMBOL(l2tp_tunnel_free);

/* Lookup a tunnel. A new reference is held on the returned tunnel. */
struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id)
{
        const struct l2tp_net *pn = l2tp_pernet(net);
        struct l2tp_tunnel *tunnel;

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

                        return tunnel;
                }
        }
        rcu_read_unlock_bh();

        return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_get);

struct l2tp_tunnel *l2tp_tunnel_get_nth(const struct net *net, int nth)
{
        const 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 &&
                    refcount_inc_not_zero(&tunnel->ref_count)) {
                        rcu_read_unlock_bh();
                        return tunnel;
                }
        }
        rcu_read_unlock_bh();

        return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_get_nth);

struct l2tp_session *l2tp_tunnel_get_session(struct l2tp_tunnel *tunnel,
                                             u32 session_id)
{
        struct hlist_head *session_list;
        struct l2tp_session *session;

        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) {
                        l2tp_session_inc_refcount(session);
                        read_unlock_bh(&tunnel->hlist_lock);

                        return session;
                }
        read_unlock_bh(&tunnel->hlist_lock);

        return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_get_session);

struct l2tp_session *l2tp_session_get(const struct net *net, u32 session_id)
{
        struct hlist_head *session_list;
        struct l2tp_session *session;

        session_list = l2tp_session_id_hash_2(l2tp_pernet(net), session_id);

        rcu_read_lock_bh();
        hlist_for_each_entry_rcu(session, session_list, global_hlist)
                if (session->session_id == session_id) {
                        l2tp_session_inc_refcount(session);
                        rcu_read_unlock_bh();

                        return session;
                }
        rcu_read_unlock_bh();

        return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_session_get);

struct l2tp_session *l2tp_session_get_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) {
                                l2tp_session_inc_refcount(session);
                                read_unlock_bh(&tunnel->hlist_lock);
                                return session;
                        }
                }
        }

        read_unlock_bh(&tunnel->hlist_lock);

        return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_session_get_nth);

/* Lookup a session by interface name.
 * This is very inefficient but is only used by management interfaces.
 */
struct l2tp_session *l2tp_session_get_by_ifname(const struct net *net,
                                                const 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)) {
                                l2tp_session_inc_refcount(session);
                                rcu_read_unlock_bh();

                                return session;
                        }
                }
        }

        rcu_read_unlock_bh();

        return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_session_get_by_ifname);

int l2tp_session_register(struct l2tp_session *session,
                          struct l2tp_tunnel *tunnel)
{
        struct l2tp_session *session_walk;
        struct hlist_head *g_head;
        struct hlist_head *head;
        struct l2tp_net *pn;
        int err;

        head = l2tp_session_id_hash(tunnel, session->session_id);

        write_lock_bh(&tunnel->hlist_lock);
        if (!tunnel->acpt_newsess) {
                err = -ENODEV;
                goto err_tlock;
        }

        hlist_for_each_entry(session_walk, head, hlist)
                if (session_walk->session_id == session->session_id) {
                        err = -EEXIST;
                        goto err_tlock;
                }

        if (tunnel->version == L2TP_HDR_VER_3) {
                pn = l2tp_pernet(tunnel->l2tp_net);
                g_head = l2tp_session_id_hash_2(pn, session->session_id);

                spin_lock_bh(&pn->l2tp_session_hlist_lock);

                hlist_for_each_entry(session_walk, g_head, global_hlist)
                        if (session_walk->session_id == session->session_id) {
                                err = -EEXIST;
                                goto err_tlock_pnlock;
                        }

                l2tp_tunnel_inc_refcount(tunnel);
                hlist_add_head_rcu(&session->global_hlist, g_head);

                spin_unlock_bh(&pn->l2tp_session_hlist_lock);
        } else {
                l2tp_tunnel_inc_refcount(tunnel);
        }

        hlist_add_head(&session->hlist, head);
        write_unlock_bh(&tunnel->hlist_lock);

        return 0;

err_tlock_pnlock:
        spin_unlock_bh(&pn->l2tp_session_hlist_lock);
err_tlock:
        write_unlock_bh(&tunnel->hlist_lock);

        return err;
}
EXPORT_SYMBOL_GPL(l2tp_session_register);

/*****************************************************************************
 * 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\n",
                                 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\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);
}

/* 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\n",
                                 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);
                        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\n",
                                         session->name, L2TP_SKB_CB(skb)->ns,
                                         L2TP_SKB_CB(skb)->length, session->nr,
                                         skb_queue_len(&session->reorder_q));
                                goto out;
                        }
                }
                __skb_unlink(skb, &session->reorder_q);

                /* Process the skb. We release the queue lock while we
                 * do so to let other contexts process the queue.
                 */
                spin_unlock_bh(&session->reorder_q.lock);
                l2tp_recv_dequeue_skb(session, skb);
                goto start;
        }

out:
        spin_unlock_bh(&session->reorder_q.lock);
}

static 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\n",
                         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\n",
                                 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\n",
                                 session->name, L2TP_SKB_CB(skb)->ns,
                                 L2TP_SKB_CB(skb)->length, session->nr,
                                 skb_queue_len(&session->reorder_q));
                        goto discard;
                }
                skb_queue_tail(&session->reorder_q, skb);
        }

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 and sublayer format 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)
{
        struct l2tp_tunnel *tunnel = session->tunnel;
        int offset;
        u32 ns, nr;

        /* 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.\n",
                                  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\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;

                        l2tp_dbg(session, L2TP_MSG_SEQ,
                                 "%s: recv data ns=%u, session nr=%u\n",
                                 session->name, ns, session->nr);
                }
                ptr += 4;
        }

        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\n",
                                  session->name);
                        session->send_seq = 1;
                        l2tp_session_set_header_len(session, tunnel->version);
                }
        } else {
                /* No sequence numbers.
                 * If user has configured mandatory sequence numbers, discard.
                 */
                if (session->recv_seq) {
                        l2tp_warn(session, L2TP_MSG_SEQ,
                                  "%s: recv data has no seq numbers when required. Discarding.\n",
                                  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\n",
                                  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.\n",
                                  session->name);
                        atomic_long_inc(&session->stats.rx_seq_discards);
                        goto discard;
                }
        }

        /* Session data offset is defined only for L2TPv2 and is
         * indicated by an optional 16-bit value in the header.
         */
        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;
                }
        }

        offset = ptr - optr;
        if (!pskb_may_pull(skb, offset))
                goto discard;

        __skb_pull(skb, offset);

        /* 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);

        return;

discard:
        atomic_long_inc(&session->stats.rx_errors);
        kfree_skb(skb);
}
EXPORT_SYMBOL(l2tp_recv_common);

/* Drop skbs from the session's reorder_q
 */
static 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);
        }
        return 0;
}

/* 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)
{
        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_MAX)) {
                l2tp_info(tunnel, L2TP_MSG_DATA,
                          "%s: recv short packet (len=%d)\n",
                          tunnel->name, skb->len);
                goto error;
        }

        /* Trace packet contents, if enabled */
        if (tunnel->debug & L2TP_MSG_DATA) {
                length = min(32u, skb->len);
                if (!pskb_may_pull(skb, length))
                        goto error;

                pr_debug("%s: recv\n", 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\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) {
                l2tp_dbg(tunnel, L2TP_MSG_DATA,
                         "%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_tunnel_get_session(tunnel, session_id);
        if (!session || !session->recv_skb) {
                if (session)
                        l2tp_session_dec_refcount(session);

                /* Not found? Pass to userspace to deal with */
                l2tp_info(tunnel, L2TP_MSG_DATA,
                          "%s: no session found (%u/%u). Passing up.\n",
                          tunnel->name, tunnel_id, session_id);
                goto error;
        }

        if (tunnel->version == L2TP_HDR_VER_3 &&
            l2tp_v3_ensure_opt_in_linear(session, skb, &ptr, &optr))
                goto error;

        l2tp_recv_common(session, skb, ptr, optr, hdrflags, length);
        l2tp_session_dec_refcount(session);

        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 = rcu_dereference_sk_user_data(sk);
        if (tunnel == NULL)
                goto pass_up;

        l2tp_dbg(tunnel, L2TP_MSG_DATA, "%s: received %d bytes\n",
                 tunnel->name, skb->len);

        if (l2tp_udp_recv_core(tunnel, skb))
                goto pass_up;

        return 0;

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\n",
                         session->name, session->ns);
        }

        return bufp - optr;
}

static int l2tp_build_l2tpv3_header(struct l2tp_session *session, void *buf)
{
        struct l2tp_tunnel *tunnel = session->tunnel;
        char *bufp = buf;
        char *optr = bufp;

        /* Setup L2TP header. The header differs slightly for UDP and
         * IP encapsulations. For UDP, there is 4 bytes of flags.
         */
        if (tunnel->encap == L2TP_ENCAPTYPE_UDP) {
                u16 flags = L2TP_HDR_VER_3;
                *((__be16 *) bufp) = htons(flags);
                bufp += 2;
                *((__be16 *) bufp) = 0;
                bufp += 2;
        }

        *((__be32 *) bufp) = htonl(session->peer_session_id);
        bufp += 4;
        if (session->cookie_len) {
                memcpy(bufp, &session->cookie[0], session->cookie_len);
                bufp += session->cookie_len;
        }
        if (session->l2specific_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\n",
                                 session->name, session->ns);
                }

                *((__be32 *)bufp) = htonl(l2h);
                bufp += 4;
        }

        return bufp - optr;
}

static void 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\n",
                         session->name, data_len, session->ns - 1);
        else
                l2tp_dbg(session, L2TP_MSG_DATA, "%s: send %zd bytes\n",
                         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\n", 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 (l2tp_sk_is_v6(tunnel->sock))
                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);
        }
}

/* 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;
        }

        /* The user-space may change the connection status for the user-space
         * provided socket at run time: we must check it under the socket lock
         */
        if (tunnel->fd >= 0 && sk->sk_state != TCP_ESTABLISHED) {
                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, 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 (l2tp_sk_is_v6(sk))
                        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);

        if (tunnel == NULL)
                goto end;

        l2tp_info(tunnel, L2TP_MSG_CONTROL, "%s: closing...\n", 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;

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

        kfree_rcu(tunnel, rcu);
end:
        return;
}

/* When the tunnel is closed, all the attached sessions need to go too.
 */
static void l2tp_tunnel_closeall(struct l2tp_tunnel *tunnel)
{
        int hash;
        struct hlist_node *walk;
        struct hlist_node *tmp;
        struct l2tp_session *session;

        BUG_ON(tunnel == NULL);

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

        write_lock_bh(&tunnel->hlist_lock);
        tunnel->acpt_newsess = false;
        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\n", session->name);

                        hlist_del_init(&session->hlist);

                        if (test_and_set_bit(0, &session->dead))
                                goto again;

                        write_unlock_bh(&tunnel->hlist_lock);

                        __l2tp_session_unhash(session);
                        l2tp_session_queue_purge(session);

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

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

        if (tunnel)
                l2tp_tunnel_delete(tunnel);
}

/* Workqueue tunnel deletion function */
static void l2tp_tunnel_del_work(struct work_struct *work)
{
        struct l2tp_tunnel *tunnel = container_of(work, struct l2tp_tunnel,
                                                  del_work);
        struct sock *sk = tunnel->sock;
        struct socket *sock = sk->sk_socket;
        struct l2tp_net *pn;

        l2tp_tunnel_closeall(tunnel);

        /* If the tunnel socket was created within the kernel, use
         * the sk API to release it here.
         */
        if (tunnel->fd < 0) {
                if (sock) {
                        kernel_sock_shutdown(sock, SHUT_RDWR);
                        sock_release(sock);
                }
        }

        /* 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);

        /* drop initial ref */
        l2tp_tunnel_dec_refcount(tunnel);

        /* drop workqueue ref */
        l2tp_tunnel_dec_refcount(tunnel);
}

/* Create a socket for the tunnel, if one isn't set up by
 * userspace. This is used for static tunnels where there is no
 * managing L2TP daemon.
 *
 * 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(net, AF_INET6, SOCK_DGRAM,
                                          IPPROTO_L2TP, &sock);
                        if (err < 0)
                                goto out;

                        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(net, AF_INET, SOCK_DGRAM,
                                          IPPROTO_L2TP, &sock);
                        if (err < 0)
                                goto out;

                        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);
                sock_release(sock);
                *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;
        enum l2tp_encap_type encap = L2TP_ENCAPTYPE_UDP;

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

        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);
        tunnel->acpt_newsess = true;

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

        tunnel->encap = encap;

        refcount_set(&tunnel->ref_count, 1);
        tunnel->fd = fd;

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

        INIT_LIST_HEAD(&tunnel->list);

        err = 0;
err:
        if (tunnelp)
                *tunnelp = tunnel;

        return err;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_create);

static int l2tp_validate_socket(const struct sock *sk, const struct net *net,
                                enum l2tp_encap_type encap)
{
        if (!net_eq(sock_net(sk), net))
                return -EINVAL;

        if (sk->sk_type != SOCK_DGRAM)
                return -EPROTONOSUPPORT;

        if ((encap == L2TP_ENCAPTYPE_UDP && sk->sk_protocol != IPPROTO_UDP) ||
            (encap == L2TP_ENCAPTYPE_IP && sk->sk_protocol != IPPROTO_L2TP))
                return -EPROTONOSUPPORT;

        if (sk->sk_user_data)
                return -EBUSY;

        return 0;
}

int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
                         struct l2tp_tunnel_cfg *cfg)
{
        struct l2tp_tunnel *tunnel_walk;
        struct l2tp_net *pn;
        struct socket *sock;
        struct sock *sk;
        int ret;

        if (tunnel->fd < 0) {
                ret = l2tp_tunnel_sock_create(net, tunnel->tunnel_id,
                                              tunnel->peer_tunnel_id, cfg,
                                              &sock);
                if (ret < 0)
                        goto err;
        } else {
                sock = sockfd_lookup(tunnel->fd, &ret);
                if (!sock)
                        goto err;

                ret = l2tp_validate_socket(sock->sk, net, tunnel->encap);
                if (ret < 0)
                        goto err_sock;
        }

        tunnel->l2tp_net = net;
        pn = l2tp_pernet(net);

        spin_lock_bh(&pn->l2tp_tunnel_list_lock);
        list_for_each_entry(tunnel_walk, &pn->l2tp_tunnel_list, list) {
                if (tunnel_walk->tunnel_id == tunnel->tunnel_id) {
                        spin_unlock_bh(&pn->l2tp_tunnel_list_lock);

                        ret = -EEXIST;
                        goto err_sock;
                }
        }
        list_add_rcu(&tunnel->list, &pn->l2tp_tunnel_list);
        spin_unlock_bh(&pn->l2tp_tunnel_list_lock);

        sk = sock->sk;
        sock_hold(sk);
        tunnel->sock = sk;

        if (tunnel->encap == L2TP_ENCAPTYPE_UDP) {
                struct udp_tunnel_sock_cfg udp_cfg = {
                        .sk_user_data = tunnel,
                        .encap_type = UDP_ENCAP_L2TPINUDP,
                        .encap_rcv = l2tp_udp_encap_recv,
                        .encap_destroy = l2tp_udp_encap_destroy,
                };

                setup_udp_tunnel_sock(net, sock, &udp_cfg);
        } else {
                sk->sk_user_data = tunnel;
        }

        tunnel->old_sk_destruct = sk->sk_destruct;
        sk->sk_destruct = &l2tp_tunnel_destruct;
        lockdep_set_class_and_name(&sk->sk_lock.slock, &l2tp_socket_class,
                                   "l2tp_sock");
        sk->sk_allocation = GFP_ATOMIC;

        if (tunnel->fd >= 0)
                sockfd_put(sock);

        return 0;

err_sock:
        if (tunnel->fd < 0)
                sock_release(sock);
        else
                sockfd_put(sock);
err:
        return ret;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_register);

/* This function is used by the netlink TUNNEL_DELETE command.
 */
void l2tp_tunnel_delete(struct l2tp_tunnel *tunnel)
{
        if (!test_and_set_bit(0, &tunnel->dead)) {
                l2tp_tunnel_inc_refcount(tunnel);
                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(refcount_read(&session->ref_count) != 0);

        if (tunnel) {
                BUG_ON(tunnel->magic != L2TP_TUNNEL_MAGIC);
                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 (test_and_set_bit(0, &session->dead))
                return 0;

        __l2tp_session_unhash(session);
        l2tp_session_queue_purge(session);
        if (session->session_close != NULL)
                (*session->session_close)(session);

        l2tp_session_dec_refcount(session);

        return 0;
}
EXPORT_SYMBOL_GPL(l2tp_session_delete);

/* We come here whenever a session's send_seq, cookie_len or
 * l2specific_type 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->hdr_len += l2tp_get_l2specific_len(session);
                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->send_seq = cfg->send_seq;
                        session->recv_seq = cfg->recv_seq;
                        session->lns_mode = cfg->lns_mode;
                        session->reorder_timeout = cfg->reorder_timeout;
                        session->l2specific_type = cfg->l2specific_type;
                        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);

                refcount_set(&session->ref_count, 1);

                return session;
        }

        return ERR_PTR(-ENOMEM);
}
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;
        int hash;

        rcu_read_lock_bh();
        list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {
                l2tp_tunnel_delete(tunnel);
        }
        rcu_read_unlock_bh();

        if (l2tp_wq)
                flush_workqueue(l2tp_wq);
        rcu_barrier();

        for (hash = 0; hash < L2TP_HASH_SIZE_2; hash++)
                WARN_ON_ONCE(!hlist_empty(&pn->l2tp_session_hlist[hash]));
}

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\n");
                unregister_pernet_device(&l2tp_net_ops);
                rc = -ENOMEM;
                goto out;
        }

        pr_info("L2TP core driver, %s\n", 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);