l2tp_eth.c

// 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 <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_sw_netstats_tx_add(dev, 1, len);
	else
		DEV_STATS_INC(dev, tx_dropped);

	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_get_stats64	= dev_get_tstats64,
	.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_TSTATS;
}

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_sw_netstats_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);