// SPDX-License-Identifier: GPL-2.0-or-later
/* L2TPv3 ethernet pseudowire driver
 *
 * Copyright (c) 2008,2009,2010 Katalix Systems Ltd
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/socket.h>
#include <linux/hash.h>
#include <linux/l2tp.h>
#include <linux/in.h>
#include <linux/etherdevice.h>
#include <linux/spinlock.h>
#include <net/sock.h>
#include <net/ip.h>
#include <net/icmp.h>
#include <net/udp.h>
#include <net/inet_common.h>
#include <net/inet_hashtables.h>
#include <net/tcp_states.h>
#include <net/protocol.h>
#include <net/xfrm.h>
#include <net/net_namespace.h>
#include <net/netns/generic.h>
#include <net/netdev_lock.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/udp.h>

#include "l2tp_core.h"

/* Default device name. May be overridden by name specified by user */
#define L2TP_ETH_DEV_NAME       "l2tpeth%d"

/* via netdev_priv() */
struct l2tp_eth {
        struct l2tp_session     *session;
};

/* via l2tp_session_priv() */
struct l2tp_eth_sess {
        struct net_device __rcu *dev;
};

static int l2tp_eth_dev_init(struct net_device *dev)
{
        eth_hw_addr_random(dev);
        eth_broadcast_addr(dev->broadcast);
        netdev_lockdep_set_classes(dev);

        return 0;
}

static void l2tp_eth_dev_uninit(struct net_device *dev)
{
        struct l2tp_eth *priv = netdev_priv(dev);
        struct l2tp_eth_sess *spriv;

        spriv = l2tp_session_priv(priv->session);
        RCU_INIT_POINTER(spriv->dev, NULL);
        /* No need for synchronize_net() here. We're called by
         * unregister_netdev*(), which does the synchronisation for us.
         */
}

static netdev_tx_t l2tp_eth_dev_xmit(struct sk_buff *skb, struct net_device *dev)
{
        struct l2tp_eth *priv = netdev_priv(dev);
        struct l2tp_session *session = priv->session;
        unsigned int len = skb->len;
        int ret = l2tp_xmit_skb(session, skb);

        if (likely(ret == NET_XMIT_SUCCESS))
                dev_dstats_tx_add(dev, len);
        else
                dev_dstats_tx_dropped(dev);

        return NETDEV_TX_OK;
}

static const struct net_device_ops l2tp_eth_netdev_ops = {
        .ndo_init               = l2tp_eth_dev_init,
        .ndo_uninit             = l2tp_eth_dev_uninit,
        .ndo_start_xmit         = l2tp_eth_dev_xmit,
        .ndo_set_mac_address    = eth_mac_addr,
};

static const struct device_type l2tpeth_type = {
        .name = "l2tpeth",
};

static void l2tp_eth_dev_setup(struct net_device *dev)
{
        SET_NETDEV_DEVTYPE(dev, &l2tpeth_type);
        ether_setup(dev);
        dev->priv_flags         &= ~IFF_TX_SKB_SHARING;
        dev->lltx               = true;
        dev->netdev_ops         = &l2tp_eth_netdev_ops;
        dev->needs_free_netdev  = true;
        dev->pcpu_stat_type     = NETDEV_PCPU_STAT_DSTATS;
}

static void l2tp_eth_dev_recv(struct l2tp_session *session, struct sk_buff *skb, int data_len)
{
        struct l2tp_eth_sess *spriv = l2tp_session_priv(session);
        struct net_device *dev;

        if (!pskb_may_pull(skb, ETH_HLEN))
                goto error;

        secpath_reset(skb);

        /* checksums verified by L2TP */
        skb->ip_summed = CHECKSUM_NONE;

        /* drop outer flow-hash */
        skb_clear_hash(skb);

        skb_dst_drop(skb);
        nf_reset_ct(skb);

        rcu_read_lock();
        dev = rcu_dereference(spriv->dev);
        if (!dev)
                goto error_rcu;

        if (dev_forward_skb(dev, skb) == NET_RX_SUCCESS)
                dev_dstats_rx_add(dev, data_len);
        else
                DEV_STATS_INC(dev, rx_errors);

        rcu_read_unlock();

        return;

error_rcu:
        rcu_read_unlock();
error:
        kfree_skb(skb);
}

static void l2tp_eth_delete(struct l2tp_session *session)
{
        struct l2tp_eth_sess *spriv;
        struct net_device *dev;

        if (session) {
                spriv = l2tp_session_priv(session);

                rtnl_lock();
                dev = rtnl_dereference(spriv->dev);
                if (dev) {
                        unregister_netdevice(dev);
                        rtnl_unlock();
                        module_put(THIS_MODULE);
                } else {
                        rtnl_unlock();
                }
        }
}

static void l2tp_eth_show(struct seq_file *m, void *arg)
{
        struct l2tp_session *session = arg;
        struct l2tp_eth_sess *spriv = l2tp_session_priv(session);
        struct net_device *dev;

        rcu_read_lock();
        dev = rcu_dereference(spriv->dev);
        if (!dev) {
                rcu_read_unlock();
                return;
        }
        dev_hold(dev);
        rcu_read_unlock();

        seq_printf(m, "   interface %s\n", dev->name);

        dev_put(dev);
}

static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel,
                                struct l2tp_session *session,
                                struct net_device *dev)
{
        unsigned int overhead = 0;
        u32 l3_overhead = 0;
        u32 mtu;

        /* if the encap is UDP, account for UDP header size */
        if (tunnel->encap == L2TP_ENCAPTYPE_UDP) {
                overhead += sizeof(struct udphdr);
                dev->needed_headroom += sizeof(struct udphdr);
        }

        lock_sock(tunnel->sock);
        l3_overhead = kernel_sock_ip_overhead(tunnel->sock);
        release_sock(tunnel->sock);

        if (l3_overhead == 0) {
                /* L3 Overhead couldn't be identified, this could be
                 * because tunnel->sock was NULL or the socket's
                 * address family was not IPv4 or IPv6,
                 * dev mtu stays at 1500.
                 */
                return;
        }
        /* Adjust MTU, factor overhead - underlay L3, overlay L2 hdr
         * UDP overhead, if any, was already factored in above.
         */
        overhead += session->hdr_len + ETH_HLEN + l3_overhead;

        mtu = l2tp_tunnel_dst_mtu(tunnel) - overhead;
        if (mtu < dev->min_mtu || mtu > dev->max_mtu)
                dev->mtu = ETH_DATA_LEN - overhead;
        else
                dev->mtu = mtu;

        dev->needed_headroom += session->hdr_len;
}

static int l2tp_eth_create(struct net *net, struct l2tp_tunnel *tunnel,
                           u32 session_id, u32 peer_session_id,
                           struct l2tp_session_cfg *cfg)
{
        unsigned char name_assign_type;
        struct net_device *dev;
        char name[IFNAMSIZ];
        struct l2tp_session *session;
        struct l2tp_eth *priv;
        struct l2tp_eth_sess *spriv;
        int rc;

        if (cfg->ifname) {
                strscpy(name, cfg->ifname, IFNAMSIZ);
                name_assign_type = NET_NAME_USER;
        } else {
                strcpy(name, L2TP_ETH_DEV_NAME);
                name_assign_type = NET_NAME_ENUM;
        }

        session = l2tp_session_create(sizeof(*spriv), tunnel, session_id,
                                      peer_session_id, cfg);
        if (IS_ERR(session)) {
                rc = PTR_ERR(session);
                goto err;
        }

        dev = alloc_netdev(sizeof(*priv), name, name_assign_type,
                           l2tp_eth_dev_setup);
        if (!dev) {
                rc = -ENOMEM;
                goto err_sess;
        }

        dev_net_set(dev, net);
        dev->min_mtu = 0;
        dev->max_mtu = ETH_MAX_MTU;
        l2tp_eth_adjust_mtu(tunnel, session, dev);

        priv = netdev_priv(dev);
        priv->session = session;

        session->recv_skb = l2tp_eth_dev_recv;
        session->session_close = l2tp_eth_delete;
        if (IS_ENABLED(CONFIG_L2TP_DEBUGFS))
                session->show = l2tp_eth_show;

        spriv = l2tp_session_priv(session);

        refcount_inc(&session->ref_count);

        rtnl_lock();

        /* Register both device and session while holding the rtnl lock. This
         * ensures that l2tp_eth_delete() will see that there's a device to
         * unregister, even if it happened to run before we assign spriv->dev.
         */
        rc = l2tp_session_register(session, tunnel);
        if (rc < 0) {
                rtnl_unlock();
                goto err_sess_dev;
        }

        rc = register_netdevice(dev);
        if (rc < 0) {
                rtnl_unlock();
                l2tp_session_delete(session);
                l2tp_session_put(session);
                free_netdev(dev);

                return rc;
        }

        strscpy(session->ifname, dev->name, IFNAMSIZ);
        rcu_assign_pointer(spriv->dev, dev);

        rtnl_unlock();

        l2tp_session_put(session);

        __module_get(THIS_MODULE);

        return 0;

err_sess_dev:
        l2tp_session_put(session);
        free_netdev(dev);
err_sess:
        l2tp_session_put(session);
err:
        return rc;
}

static const struct l2tp_nl_cmd_ops l2tp_eth_nl_cmd_ops = {
        .session_create = l2tp_eth_create,
        .session_delete = l2tp_session_delete,
};

static int __init l2tp_eth_init(void)
{
        int err = 0;

        err = l2tp_nl_register_ops(L2TP_PWTYPE_ETH, &l2tp_eth_nl_cmd_ops);
        if (err)
                goto err;

        pr_info("L2TP ethernet pseudowire support (L2TPv3)\n");

        return 0;

err:
        return err;
}

static void __exit l2tp_eth_exit(void)
{
        l2tp_nl_unregister_ops(L2TP_PWTYPE_ETH);
}

module_init(l2tp_eth_init);
module_exit(l2tp_eth_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("James Chapman <jchapman@katalix.com>");
MODULE_DESCRIPTION("L2TP ethernet pseudowire driver");
MODULE_VERSION("1.0");
MODULE_ALIAS_L2TP_PWTYPE(5);