net/ipv6/sit.c - maze/linux - Git at Google

 /*
  *	IPv6 over IPv4 tunnel device - Simple Internet Transition (SIT)
  *	Linux INET6 implementation
  *
  *	Authors:
  *	Pedro Roque		<roque@di.fc.ul.pt>
  *	Alexey Kuznetsov	<kuznet@ms2.inr.ac.ru>
  *
  *	$Id: sit.c,v 1.53 2001/09/25 05:09:53 davem Exp $
  *
  *	This program is free software; you can redistribute it and/or
  *      modify it under the terms of the GNU General Public License
  *      as published by the Free Software Foundation; either version
  *      2 of the License, or (at your option) any later version.
  *
  *	Changes:
  * Roger Venning <r.venning@telstra.com>:	6to4 support
  * Nate Thompson <nate@thebog.net>:		6to4 support
  */

 #include <linux/module.h>
 #include <linux/capability.h>
 #include <linux/errno.h>
 #include <linux/types.h>
 #include <linux/socket.h>
 #include <linux/sockios.h>
 #include <linux/sched.h>
 #include <linux/net.h>
 #include <linux/in6.h>
 #include <linux/netdevice.h>
 #include <linux/if_arp.h>
 #include <linux/icmp.h>
 #include <asm/uaccess.h>
 #include <linux/init.h>
 #include <linux/netfilter_ipv4.h>
 #include <linux/if_ether.h>

 #include <net/sock.h>
 #include <net/snmp.h>

 #include <net/ipv6.h>
 #include <net/protocol.h>
 #include <net/transp_v6.h>
 #include <net/ip6_fib.h>
 #include <net/ip6_route.h>
 #include <net/ndisc.h>
 #include <net/addrconf.h>
 #include <net/ip.h>
 #include <net/udp.h>
 #include <net/icmp.h>
 #include <net/ipip.h>
 #include <net/inet_ecn.h>
 #include <net/xfrm.h>
 #include <net/dsfield.h>

 /*
    This version of net/ipv6/sit.c is cloned of net/ipv4/ip_gre.c

    For comments look at net/ipv4/ip_gre.c --ANK
  */

 #define HASH_SIZE  16
 #define HASH(addr) (((__force u32)addr^((__force u32)addr>>4))&0xF)

 static int ipip6_fb_tunnel_init(struct net_device *dev);
 static int ipip6_tunnel_init(struct net_device *dev);
 static void ipip6_tunnel_setup(struct net_device *dev);

 static struct net_device *ipip6_fb_tunnel_dev;

 static struct ip_tunnel *tunnels_r_l[HASH_SIZE];
 static struct ip_tunnel *tunnels_r[HASH_SIZE];
 static struct ip_tunnel *tunnels_l[HASH_SIZE];
 static struct ip_tunnel *tunnels_wc[1];
 static struct ip_tunnel **tunnels[4] = { tunnels_wc, tunnels_l, tunnels_r, tunnels_r_l };

 static DEFINE_RWLOCK(ipip6_lock);

 static struct ip_tunnel * ipip6_tunnel_lookup(__be32 remote, __be32 local)
 {
 	unsigned h0 = HASH(remote);
 	unsigned h1 = HASH(local);
 	struct ip_tunnel *t;

 	for (t = tunnels_r_l[h0^h1]; t; t = t->next) {
 		if (local == t->parms.iph.saddr &&
 		    remote == t->parms.iph.daddr && (t->dev->flags&IFF_UP))
 			return t;
 	}
 	for (t = tunnels_r[h0]; t; t = t->next) {
 		if (remote == t->parms.iph.daddr && (t->dev->flags&IFF_UP))
 			return t;
 	}
 	for (t = tunnels_l[h1]; t; t = t->next) {
 		if (local == t->parms.iph.saddr && (t->dev->flags&IFF_UP))
 			return t;
 	}
 	if ((t = tunnels_wc[0]) != NULL && (t->dev->flags&IFF_UP))
 		return t;
 	return NULL;
 }

 static struct ip_tunnel ** ipip6_bucket(struct ip_tunnel *t)
 {
 	__be32 remote = t->parms.iph.daddr;
 	__be32 local = t->parms.iph.saddr;
 	unsigned h = 0;
 	int prio = 0;

 	if (remote) {
 		prio |= 2;
 		h ^= HASH(remote);
 	}
 	if (local) {
 		prio |= 1;
 		h ^= HASH(local);
 	}
 	return &tunnels[prio][h];
 }

 static void ipip6_tunnel_unlink(struct ip_tunnel *t)
 {
 	struct ip_tunnel **tp;

 	for (tp = ipip6_bucket(t); *tp; tp = &(*tp)->next) {
 		if (t == *tp) {
 			write_lock_bh(&ipip6_lock);
 			*tp = t->next;
 			write_unlock_bh(&ipip6_lock);
 			break;
 		}
 	}
 }

 static void ipip6_tunnel_link(struct ip_tunnel *t)
 {
 	struct ip_tunnel **tp = ipip6_bucket(t);

 	t->next = *tp;
 	write_lock_bh(&ipip6_lock);
 	*tp = t;
 	write_unlock_bh(&ipip6_lock);
 }

 static struct ip_tunnel * ipip6_tunnel_locate(struct ip_tunnel_parm *parms, int create)
 {
 	__be32 remote = parms->iph.daddr;
 	__be32 local = parms->iph.saddr;
 	struct ip_tunnel *t, **tp, *nt;
 	struct net_device *dev;
 	unsigned h = 0;
 	int prio = 0;
 	char name[IFNAMSIZ];

 	if (remote) {
 		prio |= 2;
 		h ^= HASH(remote);
 	}
 	if (local) {
 		prio |= 1;
 		h ^= HASH(local);
 	}
 	for (tp = &tunnels[prio][h]; (t = *tp) != NULL; tp = &t->next) {
 		if (local == t->parms.iph.saddr && remote == t->parms.iph.daddr)
 			return t;
 	}
 	if (!create)
 		goto failed;

 	if (parms->name[0])
 		strlcpy(name, parms->name, IFNAMSIZ);
 	else {
 		int i;
 		for (i=1; i<100; i++) {
 			sprintf(name, "sit%d", i);
 			if (__dev_get_by_name(name) == NULL)
 				break;
 		}
 		if (i==100)
 			goto failed;
 	}

 	dev = alloc_netdev(sizeof(*t), name, ipip6_tunnel_setup);
 	if (dev == NULL)
 		return NULL;

 	nt = netdev_priv(dev);
 	dev->init = ipip6_tunnel_init;
 	nt->parms = *parms;

 	if (register_netdevice(dev) < 0) {
 		free_netdev(dev);
 		goto failed;
 	}

 	dev_hold(dev);

 	ipip6_tunnel_link(nt);
 	return nt;

 failed:
 	return NULL;
 }

 static void ipip6_tunnel_uninit(struct net_device *dev)
 {
 	if (dev == ipip6_fb_tunnel_dev) {
 		write_lock_bh(&ipip6_lock);
 		tunnels_wc[0] = NULL;
 		write_unlock_bh(&ipip6_lock);
 		dev_put(dev);
 	} else {
 		ipip6_tunnel_unlink(netdev_priv(dev));
 		dev_put(dev);
 	}
 }


 static void ipip6_err(struct sk_buff *skb, u32 info)
 {
 #ifndef I_WISH_WORLD_WERE_PERFECT

 /* It is not :-( All the routers (except for Linux) return only
    8 bytes of packet payload. It means, that precise relaying of
    ICMP in the real Internet is absolutely infeasible.
  */
 	struct iphdr *iph = (struct iphdr*)skb->data;
 	int type = skb->h.icmph->type;
 	int code = skb->h.icmph->code;
 	struct ip_tunnel *t;

 	switch (type) {
 	default:
 	case ICMP_PARAMETERPROB:
 		return;

 	case ICMP_DEST_UNREACH:
 		switch (code) {
 		case ICMP_SR_FAILED:
 		case ICMP_PORT_UNREACH:
 			/* Impossible event. */
 			return;
 		case ICMP_FRAG_NEEDED:
 			/* Soft state for pmtu is maintained by IP core. */
 			return;
 		default:
 			/* All others are translated to HOST_UNREACH.
 			   rfc2003 contains "deep thoughts" about NET_UNREACH,
 			   I believe they are just ether pollution. --ANK
 			 */
 			break;
 		}
 		break;
 	case ICMP_TIME_EXCEEDED:
 		if (code != ICMP_EXC_TTL)
 			return;
 		break;
 	}

 	read_lock(&ipip6_lock);
 	t = ipip6_tunnel_lookup(iph->daddr, iph->saddr);
 	if (t == NULL || t->parms.iph.daddr == 0)
 		goto out;
 	if (t->parms.iph.ttl == 0 && type == ICMP_TIME_EXCEEDED)
 		goto out;

 	if (jiffies - t->err_time < IPTUNNEL_ERR_TIMEO)
 		t->err_count++;
 	else
 		t->err_count = 1;
 	t->err_time = jiffies;
 out:
 	read_unlock(&ipip6_lock);
 	return;
 #else
 	struct iphdr *iph = (struct iphdr*)dp;
 	int hlen = iph->ihl<<2;
 	struct ipv6hdr *iph6;
 	int type = skb->h.icmph->type;
 	int code = skb->h.icmph->code;
 	int rel_type = 0;
 	int rel_code = 0;
 	int rel_info = 0;
 	struct sk_buff *skb2;
 	struct rt6_info *rt6i;

 	if (len < hlen + sizeof(struct ipv6hdr))
 		return;
 	iph6 = (struct ipv6hdr*)(dp + hlen);

 	switch (type) {
 	default:
 		return;
 	case ICMP_PARAMETERPROB:
 		if (skb->h.icmph->un.gateway < hlen)
 			return;

 		/* So... This guy found something strange INSIDE encapsulated
 		   packet. Well, he is fool, but what can we do ?
 		 */
 		rel_type = ICMPV6_PARAMPROB;
 		rel_info = skb->h.icmph->un.gateway - hlen;
 		break;

 	case ICMP_DEST_UNREACH:
 		switch (code) {
 		case ICMP_SR_FAILED:
 		case ICMP_PORT_UNREACH:
 			/* Impossible event. */
 			return;
 		case ICMP_FRAG_NEEDED:
 			/* Too complicated case ... */
 			return;
 		default:
 			/* All others are translated to HOST_UNREACH.
 			   rfc2003 contains "deep thoughts" about NET_UNREACH,
 			   I believe, it is just ether pollution. --ANK
 			 */
 			rel_type = ICMPV6_DEST_UNREACH;
 			rel_code = ICMPV6_ADDR_UNREACH;
 			break;
 		}
 		break;
 	case ICMP_TIME_EXCEEDED:
 		if (code != ICMP_EXC_TTL)
 			return;
 		rel_type = ICMPV6_TIME_EXCEED;
 		rel_code = ICMPV6_EXC_HOPLIMIT;
 		break;
 	}

 	/* Prepare fake skb to feed it to icmpv6_send */
 	skb2 = skb_clone(skb, GFP_ATOMIC);
 	if (skb2 == NULL)
 		return;
 	dst_release(skb2->dst);
 	skb2->dst = NULL;
 	skb_pull(skb2, skb->data - (u8*)iph6);
 	skb2->nh.raw = skb2->data;

 	/* Try to guess incoming interface */
 	rt6i = rt6_lookup(&iph6->saddr, NULL, NULL, 0);
 	if (rt6i && rt6i->rt6i_dev) {
 		skb2->dev = rt6i->rt6i_dev;

 		rt6i = rt6_lookup(&iph6->daddr, &iph6->saddr, NULL, 0);

 		if (rt6i && rt6i->rt6i_dev && rt6i->rt6i_dev->type == ARPHRD_SIT) {
 			struct ip_tunnel *t = netdev_priv(rt6i->rt6i_dev);
 			if (rel_type == ICMPV6_TIME_EXCEED && t->parms.iph.ttl) {
 				rel_type = ICMPV6_DEST_UNREACH;
 				rel_code = ICMPV6_ADDR_UNREACH;
 			}
 			icmpv6_send(skb2, rel_type, rel_code, rel_info, skb2->dev);
 		}
 	}
 	kfree_skb(skb2);
 	return;
 #endif
 }

 static inline void ipip6_ecn_decapsulate(struct iphdr *iph, struct sk_buff *skb)
 {
 	if (INET_ECN_is_ce(iph->tos))
 		IP6_ECN_set_ce(skb->nh.ipv6h);
 }

 static int ipip6_rcv(struct sk_buff *skb)
 {
 	struct iphdr *iph;
 	struct ip_tunnel *tunnel;

 	if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
 		goto out;

 	iph = skb->nh.iph;

 	read_lock(&ipip6_lock);
 	if ((tunnel = ipip6_tunnel_lookup(iph->saddr, iph->daddr)) != NULL) {
 		secpath_reset(skb);
 		skb->mac.raw = skb->nh.raw;
 		skb->nh.raw = skb->data;
 		IPCB(skb)->flags = 0;
 		skb->protocol = htons(ETH_P_IPV6);
 		skb->pkt_type = PACKET_HOST;
 		tunnel->stat.rx_packets++;
 		tunnel->stat.rx_bytes += skb->len;
 		skb->dev = tunnel->dev;
 		dst_release(skb->dst);
 		skb->dst = NULL;
 		nf_reset(skb);
 		ipip6_ecn_decapsulate(iph, skb);
 		netif_rx(skb);
 		read_unlock(&ipip6_lock);
 		return 0;
 	}

 	icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);
 	kfree_skb(skb);
 	read_unlock(&ipip6_lock);
 out:
 	return 0;
 }

 /* Returns the embedded IPv4 address if the IPv6 address
    comes from 6to4 (RFC 3056) addr space */

 static inline __be32 try_6to4(struct in6_addr *v6dst)
 {
 	__be32 dst = 0;

 	if (v6dst->s6_addr16[0] == htons(0x2002)) {
 	        /* 6to4 v6 addr has 16 bits prefix, 32 v4addr, 16 SLA, ... */
 		memcpy(&dst, &v6dst->s6_addr16[1], 4);
 	}
 	return dst;
 }

 /*
  *	This function assumes it is being called from dev_queue_xmit()
  *	and that skb is filled properly by that function.
  */

 static int ipip6_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct ip_tunnel *tunnel = netdev_priv(dev);
 	struct net_device_stats *stats = &tunnel->stat;
 	struct iphdr  *tiph = &tunnel->parms.iph;
 	struct ipv6hdr *iph6 = skb->nh.ipv6h;
 	u8     tos = tunnel->parms.iph.tos;
 	struct rtable *rt;     			/* Route to the other host */
 	struct net_device *tdev;			/* Device to other host */
 	struct iphdr  *iph;			/* Our new IP header */
 	int    max_headroom;			/* The extra header space needed */
 	__be32 dst = tiph->daddr;
 	int    mtu;
 	struct in6_addr *addr6;
 	int addr_type;

 	if (tunnel->recursion++) {
 		tunnel->stat.collisions++;
 		goto tx_error;
 	}

 	if (skb->protocol != htons(ETH_P_IPV6))
 		goto tx_error;

 	if (!dst)
 		dst = try_6to4(&iph6->daddr);

 	if (!dst) {
 		struct neighbour *neigh = NULL;

 		if (skb->dst)
 			neigh = skb->dst->neighbour;

 		if (neigh == NULL) {
 			if (net_ratelimit())
 				printk(KERN_DEBUG "sit: nexthop == NULL\n");
 			goto tx_error;
 		}

 		addr6 = (struct in6_addr*)&neigh->primary_key;
 		addr_type = ipv6_addr_type(addr6);

 		if (addr_type == IPV6_ADDR_ANY) {
 			addr6 = &skb->nh.ipv6h->daddr;
 			addr_type = ipv6_addr_type(addr6);
 		}

 		if ((addr_type & IPV6_ADDR_COMPATv4) == 0)
 			goto tx_error_icmp;

 		dst = addr6->s6_addr32[3];
 	}

 	{
 		struct flowi fl = { .nl_u = { .ip4_u =
 					      { .daddr = dst,
 						.saddr = tiph->saddr,
 						.tos = RT_TOS(tos) } },
 				    .oif = tunnel->parms.link,
 				    .proto = IPPROTO_IPV6 };
 		if (ip_route_output_key(&rt, &fl)) {
 			tunnel->stat.tx_carrier_errors++;
 			goto tx_error_icmp;
 		}
 	}
 	if (rt->rt_type != RTN_UNICAST) {
 		ip_rt_put(rt);
 		tunnel->stat.tx_carrier_errors++;
 		goto tx_error_icmp;
 	}
 	tdev = rt->u.dst.dev;

 	if (tdev == dev) {
 		ip_rt_put(rt);
 		tunnel->stat.collisions++;
 		goto tx_error;
 	}

 	if (tiph->frag_off)
 		mtu = dst_mtu(&rt->u.dst) - sizeof(struct iphdr);
 	else
 		mtu = skb->dst ? dst_mtu(skb->dst) : dev->mtu;

 	if (mtu < 68) {
 		tunnel->stat.collisions++;
 		ip_rt_put(rt);
 		goto tx_error;
 	}
 	if (mtu < IPV6_MIN_MTU)
 		mtu = IPV6_MIN_MTU;
 	if (tunnel->parms.iph.daddr && skb->dst)
 		skb->dst->ops->update_pmtu(skb->dst, mtu);

 	if (skb->len > mtu) {
 		icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu, dev);
 		ip_rt_put(rt);
 		goto tx_error;
 	}

 	if (tunnel->err_count > 0) {
 		if (jiffies - tunnel->err_time < IPTUNNEL_ERR_TIMEO) {
 			tunnel->err_count--;
 			dst_link_failure(skb);
 		} else
 			tunnel->err_count = 0;
 	}

 	/*
 	 * Okay, now see if we can stuff it in the buffer as-is.
 	 */
 	max_headroom = LL_RESERVED_SPACE(tdev)+sizeof(struct iphdr);

 	if (skb_headroom(skb) < max_headroom || skb_cloned(skb) || skb_shared(skb)) {
 		struct sk_buff *new_skb = skb_realloc_headroom(skb, max_headroom);
 		if (!new_skb) {
 			ip_rt_put(rt);
   			stats->tx_dropped++;
 			dev_kfree_skb(skb);
 			tunnel->recursion--;
 			return 0;
 		}
 		if (skb->sk)
 			skb_set_owner_w(new_skb, skb->sk);
 		dev_kfree_skb(skb);
 		skb = new_skb;
 		iph6 = skb->nh.ipv6h;
 	}

 	skb->h.raw = skb->nh.raw;
 	skb->nh.raw = skb_push(skb, sizeof(struct iphdr));
 	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
 	IPCB(skb)->flags = 0;
 	dst_release(skb->dst);
 	skb->dst = &rt->u.dst;

 	/*
 	 *	Push down and install the IPIP header.
 	 */

 	iph 			=	skb->nh.iph;
 	iph->version		=	4;
 	iph->ihl		=	sizeof(struct iphdr)>>2;
 	if (mtu > IPV6_MIN_MTU)
 		iph->frag_off	=	htons(IP_DF);
 	else
 		iph->frag_off	=	0;

 	iph->protocol		=	IPPROTO_IPV6;
 	iph->tos		=	INET_ECN_encapsulate(tos, ipv6_get_dsfield(iph6));
 	iph->daddr		=	rt->rt_dst;
 	iph->saddr		=	rt->rt_src;

 	if ((iph->ttl = tiph->ttl) == 0)
 		iph->ttl	=	iph6->hop_limit;

 	nf_reset(skb);

 	IPTUNNEL_XMIT();
 	tunnel->recursion--;
 	return 0;

 tx_error_icmp:
 	dst_link_failure(skb);
 tx_error:
 	stats->tx_errors++;
 	dev_kfree_skb(skb);
 	tunnel->recursion--;
 	return 0;
 }

 static int
 ipip6_tunnel_ioctl (struct net_device *dev, struct ifreq *ifr, int cmd)
 {
 	int err = 0;
 	struct ip_tunnel_parm p;
 	struct ip_tunnel *t;

 	switch (cmd) {
 	case SIOCGETTUNNEL:
 		t = NULL;
 		if (dev == ipip6_fb_tunnel_dev) {
 			if (copy_from_user(&p, ifr->ifr_ifru.ifru_data, sizeof(p))) {
 				err = -EFAULT;
 				break;
 			}
 			t = ipip6_tunnel_locate(&p, 0);
 		}
 		if (t == NULL)
 			t = netdev_priv(dev);
 		memcpy(&p, &t->parms, sizeof(p));
 		if (copy_to_user(ifr->ifr_ifru.ifru_data, &p, sizeof(p)))
 			err = -EFAULT;
 		break;

 	case SIOCADDTUNNEL:
 	case SIOCCHGTUNNEL:
 		err = -EPERM;
 		if (!capable(CAP_NET_ADMIN))
 			goto done;

 		err = -EFAULT;
 		if (copy_from_user(&p, ifr->ifr_ifru.ifru_data, sizeof(p)))
 			goto done;

 		err = -EINVAL;
 		if (p.iph.version != 4 || p.iph.protocol != IPPROTO_IPV6 ||
 		    p.iph.ihl != 5 || (p.iph.frag_off&htons(~IP_DF)))
 			goto done;
 		if (p.iph.ttl)
 			p.iph.frag_off |= htons(IP_DF);

 		t = ipip6_tunnel_locate(&p, cmd == SIOCADDTUNNEL);

 		if (dev != ipip6_fb_tunnel_dev && cmd == SIOCCHGTUNNEL) {
 			if (t != NULL) {
 				if (t->dev != dev) {
 					err = -EEXIST;
 					break;
 				}
 			} else {
 				if (((dev->flags&IFF_POINTOPOINT) && !p.iph.daddr) ||
 				    (!(dev->flags&IFF_POINTOPOINT) && p.iph.daddr)) {
 					err = -EINVAL;
 					break;
 				}
 				t = netdev_priv(dev);
 				ipip6_tunnel_unlink(t);
 				t->parms.iph.saddr = p.iph.saddr;
 				t->parms.iph.daddr = p.iph.daddr;
 				memcpy(dev->dev_addr, &p.iph.saddr, 4);
 				memcpy(dev->broadcast, &p.iph.daddr, 4);
 				ipip6_tunnel_link(t);
 				netdev_state_change(dev);
 			}
 		}

 		if (t) {
 			err = 0;
 			if (cmd == SIOCCHGTUNNEL) {
 				t->parms.iph.ttl = p.iph.ttl;
 				t->parms.iph.tos = p.iph.tos;
 			}
 			if (copy_to_user(ifr->ifr_ifru.ifru_data, &t->parms, sizeof(p)))
 				err = -EFAULT;
 		} else
 			err = (cmd == SIOCADDTUNNEL ? -ENOBUFS : -ENOENT);
 		break;

 	case SIOCDELTUNNEL:
 		err = -EPERM;
 		if (!capable(CAP_NET_ADMIN))
 			goto done;

 		if (dev == ipip6_fb_tunnel_dev) {
 			err = -EFAULT;
 			if (copy_from_user(&p, ifr->ifr_ifru.ifru_data, sizeof(p)))
 				goto done;
 			err = -ENOENT;
 			if ((t = ipip6_tunnel_locate(&p, 0)) == NULL)
 				goto done;
 			err = -EPERM;
 			if (t == netdev_priv(ipip6_fb_tunnel_dev))
 				goto done;
 			dev = t->dev;
 		}
 		err = unregister_netdevice(dev);
 		break;

 	default:
 		err = -EINVAL;
 	}

 done:
 	return err;
 }

 static struct net_device_stats *ipip6_tunnel_get_stats(struct net_device *dev)
 {
 	return &(((struct ip_tunnel*)netdev_priv(dev))->stat);
 }

 static int ipip6_tunnel_change_mtu(struct net_device *dev, int new_mtu)
 {
 	if (new_mtu < IPV6_MIN_MTU || new_mtu > 0xFFF8 - sizeof(struct iphdr))
 		return -EINVAL;
 	dev->mtu = new_mtu;
 	return 0;
 }

 static void ipip6_tunnel_setup(struct net_device *dev)
 {
 	SET_MODULE_OWNER(dev);
 	dev->uninit		= ipip6_tunnel_uninit;
 	dev->destructor 	= free_netdev;
 	dev->hard_start_xmit	= ipip6_tunnel_xmit;
 	dev->get_stats		= ipip6_tunnel_get_stats;
 	dev->do_ioctl		= ipip6_tunnel_ioctl;
 	dev->change_mtu		= ipip6_tunnel_change_mtu;

 	dev->type		= ARPHRD_SIT;
 	dev->hard_header_len 	= LL_MAX_HEADER + sizeof(struct iphdr);
 	dev->mtu		= ETH_DATA_LEN - sizeof(struct iphdr);
 	dev->flags		= IFF_NOARP;
 	dev->iflink		= 0;
 	dev->addr_len		= 4;
 }

 static int ipip6_tunnel_init(struct net_device *dev)
 {
 	struct net_device *tdev = NULL;
 	struct ip_tunnel *tunnel;
 	struct iphdr *iph;

 	tunnel = netdev_priv(dev);
 	iph = &tunnel->parms.iph;

 	tunnel->dev = dev;
 	strcpy(tunnel->parms.name, dev->name);

 	memcpy(dev->dev_addr, &tunnel->parms.iph.saddr, 4);
 	memcpy(dev->broadcast, &tunnel->parms.iph.daddr, 4);

 	if (iph->daddr) {
 		struct flowi fl = { .nl_u = { .ip4_u =
 					      { .daddr = iph->daddr,
 						.saddr = iph->saddr,
 						.tos = RT_TOS(iph->tos) } },
 				    .oif = tunnel->parms.link,
 				    .proto = IPPROTO_IPV6 };
 		struct rtable *rt;
 		if (!ip_route_output_key(&rt, &fl)) {
 			tdev = rt->u.dst.dev;
 			ip_rt_put(rt);
 		}
 		dev->flags |= IFF_POINTOPOINT;
 	}

 	if (!tdev && tunnel->parms.link)
 		tdev = __dev_get_by_index(tunnel->parms.link);

 	if (tdev) {
 		dev->hard_header_len = tdev->hard_header_len + sizeof(struct iphdr);
 		dev->mtu = tdev->mtu - sizeof(struct iphdr);
 		if (dev->mtu < IPV6_MIN_MTU)
 			dev->mtu = IPV6_MIN_MTU;
 	}
 	dev->iflink = tunnel->parms.link;

 	return 0;
 }

 static int __init ipip6_fb_tunnel_init(struct net_device *dev)
 {
 	struct ip_tunnel *tunnel = netdev_priv(dev);
 	struct iphdr *iph = &tunnel->parms.iph;

 	tunnel->dev = dev;
 	strcpy(tunnel->parms.name, dev->name);

 	iph->version		= 4;
 	iph->protocol		= IPPROTO_IPV6;
 	iph->ihl		= 5;
 	iph->ttl		= 64;

 	dev_hold(dev);
 	tunnels_wc[0]		= tunnel;
 	return 0;
 }

 static struct net_protocol sit_protocol = {
 	.handler	=	ipip6_rcv,
 	.err_handler	=	ipip6_err,
 };

 static void __exit sit_destroy_tunnels(void)
 {
 	int prio;

 	for (prio = 1; prio < 4; prio++) {
 		int h;
 		for (h = 0; h < HASH_SIZE; h++) {
 			struct ip_tunnel *t;
 			while ((t = tunnels[prio][h]) != NULL)
 				unregister_netdevice(t->dev);
 		}
 	}
 }

 void __exit sit_cleanup(void)
 {
 	inet_del_protocol(&sit_protocol, IPPROTO_IPV6);

 	rtnl_lock();
 	sit_destroy_tunnels();
 	unregister_netdevice(ipip6_fb_tunnel_dev);
 	rtnl_unlock();
 }

 int __init sit_init(void)
 {
 	int err;

 	printk(KERN_INFO "IPv6 over IPv4 tunneling driver\n");

 	if (inet_add_protocol(&sit_protocol, IPPROTO_IPV6) < 0) {
 		printk(KERN_INFO "sit init: Can't add protocol\n");
 		return -EAGAIN;
 	}

 	ipip6_fb_tunnel_dev = alloc_netdev(sizeof(struct ip_tunnel), "sit0",
 					   ipip6_tunnel_setup);
 	if (!ipip6_fb_tunnel_dev) {
 		err = -ENOMEM;
 		goto err1;
 	}

 	ipip6_fb_tunnel_dev->init = ipip6_fb_tunnel_init;

 	if ((err =  register_netdev(ipip6_fb_tunnel_dev)))
 		goto err2;

  out:
 	return err;
  err2:
 	free_netdev(ipip6_fb_tunnel_dev);
  err1:
 	inet_del_protocol(&sit_protocol, IPPROTO_IPV6);
 	goto out;
 }

 module_init(sit_init);
 module_exit(sit_cleanup);
 MODULE_LICENSE("GPL");
 MODULE_ALIAS("sit0");
	/*
	* IPv6 over IPv4 tunnel device - Simple Internet Transition (SIT)
	* Linux INET6 implementation
	*
	* Authors:
	* Pedro Roque <roque@di.fc.ul.pt>
	* Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
	*
	* $Id: sit.c,v 1.53 2001/09/25 05:09:53 davem Exp $
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License
	* as published by the Free Software Foundation; either version
	* 2 of the License, or (at your option) any later version.
	*
	* Changes:
	* Roger Venning <r.venning@telstra.com>: 6to4 support
	* Nate Thompson <nate@thebog.net>: 6to4 support
	*/

	#include <linux/module.h>
	#include <linux/capability.h>
	#include <linux/errno.h>
	#include <linux/types.h>
	#include <linux/socket.h>
	#include <linux/sockios.h>
	#include <linux/sched.h>
	#include <linux/net.h>
	#include <linux/in6.h>
	#include <linux/netdevice.h>
	#include <linux/if_arp.h>
	#include <linux/icmp.h>
	#include <asm/uaccess.h>
	#include <linux/init.h>
	#include <linux/netfilter_ipv4.h>
	#include <linux/if_ether.h>

	#include <net/sock.h>
	#include <net/snmp.h>

	#include <net/ipv6.h>
	#include <net/protocol.h>
	#include <net/transp_v6.h>
	#include <net/ip6_fib.h>
	#include <net/ip6_route.h>
	#include <net/ndisc.h>
	#include <net/addrconf.h>
	#include <net/ip.h>
	#include <net/udp.h>
	#include <net/icmp.h>
	#include <net/ipip.h>
	#include <net/inet_ecn.h>
	#include <net/xfrm.h>
	#include <net/dsfield.h>

	/*
	This version of net/ipv6/sit.c is cloned of net/ipv4/ip_gre.c

	For comments look at net/ipv4/ip_gre.c --ANK
	*/

	#define HASH_SIZE 16
	#define HASH(addr) (((__force u32)addr^((__force u32)addr>>4))&0xF)

	static int ipip6_fb_tunnel_init(struct net_device *dev);
	static int ipip6_tunnel_init(struct net_device *dev);
	static void ipip6_tunnel_setup(struct net_device *dev);

	static struct net_device *ipip6_fb_tunnel_dev;

	static struct ip_tunnel *tunnels_r_l[HASH_SIZE];
	static struct ip_tunnel *tunnels_r[HASH_SIZE];
	static struct ip_tunnel *tunnels_l[HASH_SIZE];
	static struct ip_tunnel *tunnels_wc[1];
	static struct ip_tunnel **tunnels[4] = { tunnels_wc, tunnels_l, tunnels_r, tunnels_r_l };

	static DEFINE_RWLOCK(ipip6_lock);

	static struct ip_tunnel * ipip6_tunnel_lookup(__be32 remote, __be32 local)
	{
	unsigned h0 = HASH(remote);
	unsigned h1 = HASH(local);
	struct ip_tunnel *t;

	for (t = tunnels_r_l[h0^h1]; t; t = t->next) {
	if (local == t->parms.iph.saddr &&
	remote == t->parms.iph.daddr && (t->dev->flags&IFF_UP))
	return t;
	}
	for (t = tunnels_r[h0]; t; t = t->next) {
	if (remote == t->parms.iph.daddr && (t->dev->flags&IFF_UP))
	return t;
	}
	for (t = tunnels_l[h1]; t; t = t->next) {
	if (local == t->parms.iph.saddr && (t->dev->flags&IFF_UP))
	return t;
	}
	if ((t = tunnels_wc[0]) != NULL && (t->dev->flags&IFF_UP))
	return t;
	return NULL;
	}

	static struct ip_tunnel ** ipip6_bucket(struct ip_tunnel *t)
	{
	__be32 remote = t->parms.iph.daddr;
	__be32 local = t->parms.iph.saddr;
	unsigned h = 0;
	int prio = 0;

	if (remote) {
	prio \|= 2;
	h ^= HASH(remote);
	}
	if (local) {
	prio \|= 1;
	h ^= HASH(local);
	}
	return &tunnels[prio][h];
	}

	static void ipip6_tunnel_unlink(struct ip_tunnel *t)
	{
	struct ip_tunnel **tp;

	for (tp = ipip6_bucket(t); tp; tp = &(tp)->next) {
	if (t == *tp) {
	write_lock_bh(&ipip6_lock);
	*tp = t->next;
	write_unlock_bh(&ipip6_lock);
	break;
	}
	}
	}

	static void ipip6_tunnel_link(struct ip_tunnel *t)
	{
	struct ip_tunnel **tp = ipip6_bucket(t);

	t->next = *tp;
	write_lock_bh(&ipip6_lock);
	*tp = t;
	write_unlock_bh(&ipip6_lock);
	}

	static struct ip_tunnel * ipip6_tunnel_locate(struct ip_tunnel_parm *parms, int create)
	{
	__be32 remote = parms->iph.daddr;
	__be32 local = parms->iph.saddr;
	struct ip_tunnel t, tp, nt;
	struct net_device *dev;
	unsigned h = 0;
	int prio = 0;
	char name[IFNAMSIZ];

	if (remote) {
	prio \|= 2;
	h ^= HASH(remote);
	}
	if (local) {
	prio \|= 1;
	h ^= HASH(local);
	}
	for (tp = &tunnels[prio][h]; (t = *tp) != NULL; tp = &t->next) {
	if (local == t->parms.iph.saddr && remote == t->parms.iph.daddr)
	return t;
	}
	if (!create)
	goto failed;

	if (parms->name[0])
	strlcpy(name, parms->name, IFNAMSIZ);
	else {
	int i;
	for (i=1; i<100; i++) {
	sprintf(name, "sit%d", i);
	if (__dev_get_by_name(name) == NULL)
	break;
	}
	if (i==100)
	goto failed;
	}

	dev = alloc_netdev(sizeof(*t), name, ipip6_tunnel_setup);
	if (dev == NULL)
	return NULL;

	nt = netdev_priv(dev);
	dev->init = ipip6_tunnel_init;
	nt->parms = *parms;

	if (register_netdevice(dev) < 0) {
	free_netdev(dev);
	goto failed;
	}

	dev_hold(dev);

	ipip6_tunnel_link(nt);
	return nt;

	failed:
	return NULL;
	}

	static void ipip6_tunnel_uninit(struct net_device *dev)
	{
	if (dev == ipip6_fb_tunnel_dev) {
	write_lock_bh(&ipip6_lock);
	tunnels_wc[0] = NULL;
	write_unlock_bh(&ipip6_lock);
	dev_put(dev);
	} else {
	ipip6_tunnel_unlink(netdev_priv(dev));
	dev_put(dev);
	}
	}


	static void ipip6_err(struct sk_buff *skb, u32 info)
	{
	#ifndef I_WISH_WORLD_WERE_PERFECT

	/* It is not :-( All the routers (except for Linux) return only
	8 bytes of packet payload. It means, that precise relaying of
	ICMP in the real Internet is absolutely infeasible.
	*/
	struct iphdr iph = (struct iphdr)skb->data;
	int type = skb->h.icmph->type;
	int code = skb->h.icmph->code;
	struct ip_tunnel *t;

	switch (type) {
	default:
	case ICMP_PARAMETERPROB:
	return;

	case ICMP_DEST_UNREACH:
	switch (code) {
	case ICMP_SR_FAILED:
	case ICMP_PORT_UNREACH:
	/* Impossible event. */
	return;
	case ICMP_FRAG_NEEDED:
	/* Soft state for pmtu is maintained by IP core. */
	return;
	default:
	/* All others are translated to HOST_UNREACH.
	rfc2003 contains "deep thoughts" about NET_UNREACH,
	I believe they are just ether pollution. --ANK
	*/
	break;
	}
	break;
	case ICMP_TIME_EXCEEDED:
	if (code != ICMP_EXC_TTL)
	return;
	break;
	}

	read_lock(&ipip6_lock);
	t = ipip6_tunnel_lookup(iph->daddr, iph->saddr);
	if (t == NULL \|\| t->parms.iph.daddr == 0)
	goto out;
	if (t->parms.iph.ttl == 0 && type == ICMP_TIME_EXCEEDED)
	goto out;

	if (jiffies - t->err_time < IPTUNNEL_ERR_TIMEO)
	t->err_count++;
	else
	t->err_count = 1;
	t->err_time = jiffies;
	out:
	read_unlock(&ipip6_lock);
	return;
	#else
	struct iphdr iph = (struct iphdr)dp;
	int hlen = iph->ihl<<2;
	struct ipv6hdr *iph6;
	int type = skb->h.icmph->type;
	int code = skb->h.icmph->code;
	int rel_type = 0;
	int rel_code = 0;
	int rel_info = 0;
	struct sk_buff *skb2;
	struct rt6_info *rt6i;

	if (len < hlen + sizeof(struct ipv6hdr))
	return;
	iph6 = (struct ipv6hdr*)(dp + hlen);

	switch (type) {
	default:
	return;
	case ICMP_PARAMETERPROB:
	if (skb->h.icmph->un.gateway < hlen)
	return;

	/* So... This guy found something strange INSIDE encapsulated
	packet. Well, he is fool, but what can we do ?
	*/
	rel_type = ICMPV6_PARAMPROB;
	rel_info = skb->h.icmph->un.gateway - hlen;
	break;

	case ICMP_DEST_UNREACH:
	switch (code) {
	case ICMP_SR_FAILED:
	case ICMP_PORT_UNREACH:
	/* Impossible event. */
	return;
	case ICMP_FRAG_NEEDED:
	/* Too complicated case ... */
	return;
	default:
	/* All others are translated to HOST_UNREACH.
	rfc2003 contains "deep thoughts" about NET_UNREACH,
	I believe, it is just ether pollution. --ANK
	*/
	rel_type = ICMPV6_DEST_UNREACH;
	rel_code = ICMPV6_ADDR_UNREACH;
	break;
	}
	break;
	case ICMP_TIME_EXCEEDED:
	if (code != ICMP_EXC_TTL)
	return;
	rel_type = ICMPV6_TIME_EXCEED;
	rel_code = ICMPV6_EXC_HOPLIMIT;
	break;
	}

	/* Prepare fake skb to feed it to icmpv6_send */
	skb2 = skb_clone(skb, GFP_ATOMIC);
	if (skb2 == NULL)
	return;
	dst_release(skb2->dst);
	skb2->dst = NULL;
	skb_pull(skb2, skb->data - (u8*)iph6);
	skb2->nh.raw = skb2->data;

	/* Try to guess incoming interface */
	rt6i = rt6_lookup(&iph6->saddr, NULL, NULL, 0);
	if (rt6i && rt6i->rt6i_dev) {
	skb2->dev = rt6i->rt6i_dev;

	rt6i = rt6_lookup(&iph6->daddr, &iph6->saddr, NULL, 0);

	if (rt6i && rt6i->rt6i_dev && rt6i->rt6i_dev->type == ARPHRD_SIT) {
	struct ip_tunnel *t = netdev_priv(rt6i->rt6i_dev);
	if (rel_type == ICMPV6_TIME_EXCEED && t->parms.iph.ttl) {
	rel_type = ICMPV6_DEST_UNREACH;
	rel_code = ICMPV6_ADDR_UNREACH;
	}
	icmpv6_send(skb2, rel_type, rel_code, rel_info, skb2->dev);
	}
	}
	kfree_skb(skb2);
	return;
	#endif
	}

	static inline void ipip6_ecn_decapsulate(struct iphdr iph, struct sk_buff skb)
	{
	if (INET_ECN_is_ce(iph->tos))
	IP6_ECN_set_ce(skb->nh.ipv6h);
	}

	static int ipip6_rcv(struct sk_buff *skb)
	{
	struct iphdr *iph;
	struct ip_tunnel *tunnel;

	if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
	goto out;

	iph = skb->nh.iph;

	read_lock(&ipip6_lock);
	if ((tunnel = ipip6_tunnel_lookup(iph->saddr, iph->daddr)) != NULL) {
	secpath_reset(skb);
	skb->mac.raw = skb->nh.raw;
	skb->nh.raw = skb->data;
	IPCB(skb)->flags = 0;
	skb->protocol = htons(ETH_P_IPV6);
	skb->pkt_type = PACKET_HOST;
	tunnel->stat.rx_packets++;
	tunnel->stat.rx_bytes += skb->len;
	skb->dev = tunnel->dev;
	dst_release(skb->dst);
	skb->dst = NULL;
	nf_reset(skb);
	ipip6_ecn_decapsulate(iph, skb);
	netif_rx(skb);
	read_unlock(&ipip6_lock);
	return 0;
	}

	icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);
	kfree_skb(skb);
	read_unlock(&ipip6_lock);
	out:
	return 0;
	}

	/* Returns the embedded IPv4 address if the IPv6 address
	comes from 6to4 (RFC 3056) addr space */

	static inline __be32 try_6to4(struct in6_addr *v6dst)
	{
	__be32 dst = 0;

	if (v6dst->s6_addr16[0] == htons(0x2002)) {
	/* 6to4 v6 addr has 16 bits prefix, 32 v4addr, 16 SLA, ... */
	memcpy(&dst, &v6dst->s6_addr16[1], 4);
	}
	return dst;
	}

	/*
	* This function assumes it is being called from dev_queue_xmit()
	* and that skb is filled properly by that function.
	*/

	static int ipip6_tunnel_xmit(struct sk_buff skb, struct net_device dev)
	{
	struct ip_tunnel *tunnel = netdev_priv(dev);
	struct net_device_stats *stats = &tunnel->stat;
	struct iphdr *tiph = &tunnel->parms.iph;
	struct ipv6hdr *iph6 = skb->nh.ipv6h;
	u8 tos = tunnel->parms.iph.tos;
	struct rtable rt; / Route to the other host */
	struct net_device tdev; / Device to other host */
	struct iphdr iph; / Our new IP header */
	int max_headroom; /* The extra header space needed */
	__be32 dst = tiph->daddr;
	int mtu;
	struct in6_addr *addr6;
	int addr_type;

	if (tunnel->recursion++) {
	tunnel->stat.collisions++;
	goto tx_error;
	}

	if (skb->protocol != htons(ETH_P_IPV6))
	goto tx_error;

	if (!dst)
	dst = try_6to4(&iph6->daddr);

	if (!dst) {
	struct neighbour *neigh = NULL;

	if (skb->dst)
	neigh = skb->dst->neighbour;

	if (neigh == NULL) {
	if (net_ratelimit())
	printk(KERN_DEBUG "sit: nexthop == NULL\n");
	goto tx_error;
	}

	addr6 = (struct in6_addr*)&neigh->primary_key;
	addr_type = ipv6_addr_type(addr6);

	if (addr_type == IPV6_ADDR_ANY) {
	addr6 = &skb->nh.ipv6h->daddr;
	addr_type = ipv6_addr_type(addr6);
	}

	if ((addr_type & IPV6_ADDR_COMPATv4) == 0)
	goto tx_error_icmp;

	dst = addr6->s6_addr32[3];
	}

	{
	struct flowi fl = { .nl_u = { .ip4_u =
	{ .daddr = dst,
	.saddr = tiph->saddr,
	.tos = RT_TOS(tos) } },
	.oif = tunnel->parms.link,
	.proto = IPPROTO_IPV6 };
	if (ip_route_output_key(&rt, &fl)) {
	tunnel->stat.tx_carrier_errors++;
	goto tx_error_icmp;
	}
	}
	if (rt->rt_type != RTN_UNICAST) {
	ip_rt_put(rt);
	tunnel->stat.tx_carrier_errors++;
	goto tx_error_icmp;
	}
	tdev = rt->u.dst.dev;

	if (tdev == dev) {
	ip_rt_put(rt);
	tunnel->stat.collisions++;
	goto tx_error;
	}

	if (tiph->frag_off)
	mtu = dst_mtu(&rt->u.dst) - sizeof(struct iphdr);
	else
	mtu = skb->dst ? dst_mtu(skb->dst) : dev->mtu;

	if (mtu < 68) {
	tunnel->stat.collisions++;
	ip_rt_put(rt);
	goto tx_error;
	}
	if (mtu < IPV6_MIN_MTU)
	mtu = IPV6_MIN_MTU;
	if (tunnel->parms.iph.daddr && skb->dst)
	skb->dst->ops->update_pmtu(skb->dst, mtu);

	if (skb->len > mtu) {
	icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu, dev);
	ip_rt_put(rt);
	goto tx_error;
	}

	if (tunnel->err_count > 0) {
	if (jiffies - tunnel->err_time < IPTUNNEL_ERR_TIMEO) {
	tunnel->err_count--;
	dst_link_failure(skb);
	} else
	tunnel->err_count = 0;
	}

	/*
	* Okay, now see if we can stuff it in the buffer as-is.
	*/
	max_headroom = LL_RESERVED_SPACE(tdev)+sizeof(struct iphdr);

	if (skb_headroom(skb) < max_headroom \|\| skb_cloned(skb) \|\| skb_shared(skb)) {
	struct sk_buff *new_skb = skb_realloc_headroom(skb, max_headroom);
	if (!new_skb) {
	ip_rt_put(rt);
	stats->tx_dropped++;
	dev_kfree_skb(skb);
	tunnel->recursion--;
	return 0;
	}
	if (skb->sk)
	skb_set_owner_w(new_skb, skb->sk);
	dev_kfree_skb(skb);
	skb = new_skb;
	iph6 = skb->nh.ipv6h;
	}

	skb->h.raw = skb->nh.raw;
	skb->nh.raw = skb_push(skb, sizeof(struct iphdr));
	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
	IPCB(skb)->flags = 0;
	dst_release(skb->dst);
	skb->dst = &rt->u.dst;

	/*
	* Push down and install the IPIP header.
	*/

	iph = skb->nh.iph;
	iph->version = 4;
	iph->ihl = sizeof(struct iphdr)>>2;
	if (mtu > IPV6_MIN_MTU)
	iph->frag_off = htons(IP_DF);
	else
	iph->frag_off = 0;

	iph->protocol = IPPROTO_IPV6;
	iph->tos = INET_ECN_encapsulate(tos, ipv6_get_dsfield(iph6));
	iph->daddr = rt->rt_dst;
	iph->saddr = rt->rt_src;

	if ((iph->ttl = tiph->ttl) == 0)
	iph->ttl = iph6->hop_limit;

	nf_reset(skb);

	IPTUNNEL_XMIT();
	tunnel->recursion--;
	return 0;

	tx_error_icmp:
	dst_link_failure(skb);
	tx_error:
	stats->tx_errors++;
	dev_kfree_skb(skb);
	tunnel->recursion--;
	return 0;
	}

	static int
	ipip6_tunnel_ioctl (struct net_device dev, struct ifreq ifr, int cmd)
	{
	int err = 0;
	struct ip_tunnel_parm p;
	struct ip_tunnel *t;

	switch (cmd) {
	case SIOCGETTUNNEL:
	t = NULL;
	if (dev == ipip6_fb_tunnel_dev) {
	if (copy_from_user(&p, ifr->ifr_ifru.ifru_data, sizeof(p))) {
	err = -EFAULT;
	break;
	}
	t = ipip6_tunnel_locate(&p, 0);
	}
	if (t == NULL)
	t = netdev_priv(dev);
	memcpy(&p, &t->parms, sizeof(p));
	if (copy_to_user(ifr->ifr_ifru.ifru_data, &p, sizeof(p)))
	err = -EFAULT;
	break;

	case SIOCADDTUNNEL:
	case SIOCCHGTUNNEL:
	err = -EPERM;
	if (!capable(CAP_NET_ADMIN))
	goto done;

	err = -EFAULT;
	if (copy_from_user(&p, ifr->ifr_ifru.ifru_data, sizeof(p)))
	goto done;

	err = -EINVAL;
	if (p.iph.version != 4 \|\| p.iph.protocol != IPPROTO_IPV6 \|\|
	p.iph.ihl != 5 \|\| (p.iph.frag_off&htons(~IP_DF)))
	goto done;
	if (p.iph.ttl)
	p.iph.frag_off \|= htons(IP_DF);

	t = ipip6_tunnel_locate(&p, cmd == SIOCADDTUNNEL);

	if (dev != ipip6_fb_tunnel_dev && cmd == SIOCCHGTUNNEL) {
	if (t != NULL) {
	if (t->dev != dev) {
	err = -EEXIST;
	break;
	}
	} else {
	if (((dev->flags&IFF_POINTOPOINT) && !p.iph.daddr) \|\|
	(!(dev->flags&IFF_POINTOPOINT) && p.iph.daddr)) {
	err = -EINVAL;
	break;
	}
	t = netdev_priv(dev);
	ipip6_tunnel_unlink(t);
	t->parms.iph.saddr = p.iph.saddr;
	t->parms.iph.daddr = p.iph.daddr;
	memcpy(dev->dev_addr, &p.iph.saddr, 4);
	memcpy(dev->broadcast, &p.iph.daddr, 4);
	ipip6_tunnel_link(t);
	netdev_state_change(dev);
	}
	}

	if (t) {
	err = 0;
	if (cmd == SIOCCHGTUNNEL) {
	t->parms.iph.ttl = p.iph.ttl;
	t->parms.iph.tos = p.iph.tos;
	}
	if (copy_to_user(ifr->ifr_ifru.ifru_data, &t->parms, sizeof(p)))
	err = -EFAULT;
	} else
	err = (cmd == SIOCADDTUNNEL ? -ENOBUFS : -ENOENT);
	break;

	case SIOCDELTUNNEL:
	err = -EPERM;
	if (!capable(CAP_NET_ADMIN))
	goto done;

	if (dev == ipip6_fb_tunnel_dev) {
	err = -EFAULT;
	if (copy_from_user(&p, ifr->ifr_ifru.ifru_data, sizeof(p)))
	goto done;
	err = -ENOENT;
	if ((t = ipip6_tunnel_locate(&p, 0)) == NULL)
	goto done;
	err = -EPERM;
	if (t == netdev_priv(ipip6_fb_tunnel_dev))
	goto done;
	dev = t->dev;
	}
	err = unregister_netdevice(dev);
	break;

	default:
	err = -EINVAL;
	}

	done:
	return err;
	}

	static struct net_device_stats ipip6_tunnel_get_stats(struct net_device dev)
	{
	return &(((struct ip_tunnel*)netdev_priv(dev))->stat);
	}

	static int ipip6_tunnel_change_mtu(struct net_device *dev, int new_mtu)
	{
	if (new_mtu < IPV6_MIN_MTU \|\| new_mtu > 0xFFF8 - sizeof(struct iphdr))
	return -EINVAL;
	dev->mtu = new_mtu;
	return 0;
	}

	static void ipip6_tunnel_setup(struct net_device *dev)
	{
	SET_MODULE_OWNER(dev);
	dev->uninit = ipip6_tunnel_uninit;
	dev->destructor = free_netdev;
	dev->hard_start_xmit = ipip6_tunnel_xmit;
	dev->get_stats = ipip6_tunnel_get_stats;
	dev->do_ioctl = ipip6_tunnel_ioctl;
	dev->change_mtu = ipip6_tunnel_change_mtu;

	dev->type = ARPHRD_SIT;
	dev->hard_header_len = LL_MAX_HEADER + sizeof(struct iphdr);
	dev->mtu = ETH_DATA_LEN - sizeof(struct iphdr);
	dev->flags = IFF_NOARP;
	dev->iflink = 0;
	dev->addr_len = 4;
	}

	static int ipip6_tunnel_init(struct net_device *dev)
	{
	struct net_device *tdev = NULL;
	struct ip_tunnel *tunnel;
	struct iphdr *iph;

	tunnel = netdev_priv(dev);
	iph = &tunnel->parms.iph;

	tunnel->dev = dev;
	strcpy(tunnel->parms.name, dev->name);

	memcpy(dev->dev_addr, &tunnel->parms.iph.saddr, 4);
	memcpy(dev->broadcast, &tunnel->parms.iph.daddr, 4);

	if (iph->daddr) {
	struct flowi fl = { .nl_u = { .ip4_u =
	{ .daddr = iph->daddr,
	.saddr = iph->saddr,
	.tos = RT_TOS(iph->tos) } },
	.oif = tunnel->parms.link,
	.proto = IPPROTO_IPV6 };
	struct rtable *rt;
	if (!ip_route_output_key(&rt, &fl)) {
	tdev = rt->u.dst.dev;
	ip_rt_put(rt);
	}
	dev->flags \|= IFF_POINTOPOINT;
	}

	if (!tdev && tunnel->parms.link)
	tdev = __dev_get_by_index(tunnel->parms.link);

	if (tdev) {
	dev->hard_header_len = tdev->hard_header_len + sizeof(struct iphdr);
	dev->mtu = tdev->mtu - sizeof(struct iphdr);
	if (dev->mtu < IPV6_MIN_MTU)
	dev->mtu = IPV6_MIN_MTU;
	}
	dev->iflink = tunnel->parms.link;

	return 0;
	}

	static int __init ipip6_fb_tunnel_init(struct net_device *dev)
	{
	struct ip_tunnel *tunnel = netdev_priv(dev);
	struct iphdr *iph = &tunnel->parms.iph;

	tunnel->dev = dev;
	strcpy(tunnel->parms.name, dev->name);

	iph->version = 4;
	iph->protocol = IPPROTO_IPV6;
	iph->ihl = 5;
	iph->ttl = 64;

	dev_hold(dev);
	tunnels_wc[0] = tunnel;
	return 0;
	}

	static struct net_protocol sit_protocol = {
	.handler = ipip6_rcv,
	.err_handler = ipip6_err,
	};

	static void __exit sit_destroy_tunnels(void)
	{
	int prio;

	for (prio = 1; prio < 4; prio++) {
	int h;
	for (h = 0; h < HASH_SIZE; h++) {
	struct ip_tunnel *t;
	while ((t = tunnels[prio][h]) != NULL)
	unregister_netdevice(t->dev);
	}
	}
	}

	void __exit sit_cleanup(void)
	{
	inet_del_protocol(&sit_protocol, IPPROTO_IPV6);

	rtnl_lock();
	sit_destroy_tunnels();
	unregister_netdevice(ipip6_fb_tunnel_dev);
	rtnl_unlock();
	}

	int __init sit_init(void)
	{
	int err;

	printk(KERN_INFO "IPv6 over IPv4 tunneling driver\n");

	if (inet_add_protocol(&sit_protocol, IPPROTO_IPV6) < 0) {
	printk(KERN_INFO "sit init: Can't add protocol\n");
	return -EAGAIN;
	}

	ipip6_fb_tunnel_dev = alloc_netdev(sizeof(struct ip_tunnel), "sit0",
	ipip6_tunnel_setup);
	if (!ipip6_fb_tunnel_dev) {
	err = -ENOMEM;
	goto err1;
	}

	ipip6_fb_tunnel_dev->init = ipip6_fb_tunnel_init;

	if ((err = register_netdev(ipip6_fb_tunnel_dev)))
	goto err2;

	out:
	return err;
	err2:
	free_netdev(ipip6_fb_tunnel_dev);
	err1:
	inet_del_protocol(&sit_protocol, IPPROTO_IPV6);
	goto out;
	}

	module_init(sit_init);
	module_exit(sit_cleanup);
	MODULE_LICENSE("GPL");
	MODULE_ALIAS("sit0");