sit.c

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/*
 *      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 1.31 1999/03/25 10:04:55 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.
 */

#define __NO_VERSION__
#include <linux/module.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 <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>

/*
   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) ((addr^(addr>>4))&0xF)

static int ipip6_fb_tunnel_init(struct device *dev);
static int ipip6_tunnel_init(struct device *dev);

static struct device ipip6_fb_tunnel_dev = {
        NULL, 0x0, 0x0, 0x0, 0x0, 0, 0, 0, 0, 0, NULL, ipip6_fb_tunnel_init,
};

static struct ip_tunnel ipip6_fb_tunnel = {
        NULL, &ipip6_fb_tunnel_dev, {0, }, 0, 0, 0, 0, 0, 0, 0, {"sit0", }
};

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 struct ip_tunnel * ipip6_tunnel_lookup(u32 remote, u32 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)
{
        u32 remote = t->parms.iph.daddr;
        u32 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) {
                        *tp = t->next;
                        synchronize_bh();
                        break;
                }
        }
}

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

        t->next = *tp;
        wmb();
        *tp = t;
}

struct ip_tunnel * ipip6_tunnel_locate(struct ip_tunnel_parm *parms, int create)
{
        u32 remote = parms->iph.daddr;
        u32 local = parms->iph.saddr;
        struct ip_tunnel *t, **tp, *nt;
        struct device *dev;
        unsigned h = 0;
        int prio = 0;

        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)
                return NULL;

        MOD_INC_USE_COUNT;
        dev = kmalloc(sizeof(*dev) + sizeof(*t), GFP_KERNEL);
        if (dev == NULL) {
                MOD_DEC_USE_COUNT;
                return NULL;
        }
        memset(dev, 0, sizeof(*dev) + sizeof(*t));
        dev->priv = (void*)(dev+1);
        nt = (struct ip_tunnel*)dev->priv;
        nt->dev = dev;
        dev->name = nt->parms.name;
        dev->init = ipip6_tunnel_init;
        memcpy(&nt->parms, parms, sizeof(*parms));
        if (dev->name[0] == 0) {
                int i;
                for (i=1; i<100; i++) {
                        sprintf(dev->name, "sit%d", i);
                        if (dev_get(dev->name) == NULL)
                                break;
                }
                if (i==100)
                        goto failed;
                memcpy(parms->name, dev->name, IFNAMSIZ);
        }
        if (register_netdevice(dev) < 0)
                goto failed;

        ipip6_tunnel_link(nt);
        /* Do not decrement MOD_USE_COUNT here. */
        return nt;

failed:
        kfree(dev);
        MOD_DEC_USE_COUNT;
        return NULL;
}

static void ipip6_tunnel_destroy(struct device *dev)
{
        if (dev == &ipip6_fb_tunnel_dev) {
                tunnels_wc[0] = NULL;
                synchronize_bh();
                return;
        } else {
                ipip6_tunnel_unlink((struct ip_tunnel*)dev->priv);
                kfree(dev);
                MOD_DEC_USE_COUNT;
        }
}

void ipip6_err(struct sk_buff *skb, unsigned char *dp, int len)
{
#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*)dp;
        int type = skb->h.icmph->type;
        int code = skb->h.icmph->code;
        struct ip_tunnel *t;

        if (len < sizeof(struct iphdr))
                return;

        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;
        }

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

        if (jiffies - t->err_time < IPTUNNEL_ERR_TIMEO)
                t->err_count++;
        else
                t->err_count = 1;
        t->err_time = jiffies;
        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 = (struct ip_tunnel*)rt6i->rt6i_dev->priv;
                        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
}

int ipip6_rcv(struct sk_buff *skb, unsigned short len)
{
        struct iphdr *iph;
        struct ip_tunnel *tunnel;

        iph = skb->nh.iph;

        if ((tunnel = ipip6_tunnel_lookup(iph->saddr, iph->daddr)) != NULL) {
                skb->mac.raw = skb->nh.raw;
                skb->nh.raw = skb_pull(skb, skb->h.raw - skb->data);
                memset(&(IPCB(skb)->opt), 0, sizeof(struct ip_options));
                skb->protocol = __constant_htons(ETH_P_IPV6);
                skb->ip_summed = 0;
                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;
                netif_rx(skb);
                return 0;
        }

        icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PROT_UNREACH, 0);
        kfree_skb(skb);
        return 0;
}

/*
 *      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 device *dev)
{
        struct ip_tunnel *tunnel = (struct ip_tunnel*)dev->priv;
        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 device *tdev;                    /* Device to other host */
        struct iphdr  *iph;                     /* Our new IP header */
        int    max_headroom;                    /* The extra header space needed */
        u32    dst = tiph->daddr;
        int    mtu;
        struct in6_addr *addr6; 
        int addr_type;

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

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

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

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

                if (neigh == NULL) {
                        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];
        }

        if (ip_route_output(&rt, dst, tiph->saddr, RT_TOS(tos), tunnel->parms.link)) {
                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;
        }

        mtu = rt->u.dst.pmtu - sizeof(struct iphdr);
        if (mtu < 68) {
                tunnel->stat.collisions++;
                ip_rt_put(rt);
                goto tx_error;
        }
        if (mtu < IPV6_MIN_MTU)
                mtu = IPV6_MIN_MTU;
        if (skb->dst && mtu < skb->dst->pmtu) {
                struct rt6_info *rt6 = (struct rt6_info*)skb->dst;
                if (mtu < rt6->u.dst.pmtu) {
                        if (tunnel->parms.iph.daddr || rt6->rt6i_dst.plen == 128) {
                                rt6->rt6i_flags |= RTF_MODIFIED;
                                rt6->u.dst.pmtu = 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;
        }

        skb->h.raw = skb->nh.raw;

        /*
         * Okay, now see if we can stuff it in the buffer as-is.
         */
        max_headroom = (((tdev->hard_header_len+15)&~15)+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;
        }

        skb->nh.raw = skb_push(skb, sizeof(struct iphdr));
        memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
        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   =       __constant_htons(IP_DF);
        else
                iph->frag_off   =       0;

        iph->protocol           =       IPPROTO_IPV6;
        iph->tos                =       tos;
        iph->daddr              =       rt->rt_dst;
        iph->saddr              =       rt->rt_src;

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

        iph->tot_len            =       htons(skb->len);
        iph->id                 =       htons(ip_id_count++);
        ip_send_check(iph);

        stats->tx_bytes += skb->len;
        stats->tx_packets++;
        ip_send(skb);

        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 device *dev, struct ifreq *ifr, int cmd)
{
        int err = 0;
        struct ip_tunnel_parm p;
        struct ip_tunnel *t;

        MOD_INC_USE_COUNT;

        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 = (struct ip_tunnel*)dev->priv;
                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&__constant_htons(~IP_DF)))
                        goto done;
                if (p.iph.ttl)
                        p.iph.frag_off |= __constant_htons(IP_DF);

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

                if (dev != &ipip6_fb_tunnel_dev && cmd == SIOCCHGTUNNEL &&
                    t != &ipip6_fb_tunnel) {
                        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 = (struct ip_tunnel*)dev->priv;
                                start_bh_atomic();
                                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);
                                end_bh_atomic();
                                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 == &ipip6_fb_tunnel)
                                goto done;
                }
                err = unregister_netdevice(dev);
                break;

        default:
                err = -EINVAL;
        }

done:
        MOD_DEC_USE_COUNT;
        return err;
}

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

static int ipip6_tunnel_change_mtu(struct 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_init_gen(struct device *dev)
{
        struct ip_tunnel *t = (struct ip_tunnel*)dev->priv;

        dev->destructor         = ipip6_tunnel_destroy;
        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_init_buffers(dev);

        dev->type               = ARPHRD_SIT;
        dev->hard_header_len    = LL_MAX_HEADER + sizeof(struct iphdr);
        dev->mtu                = 1500 - sizeof(struct iphdr);
        dev->flags              = IFF_NOARP;
        dev->iflink             = 0;
        dev->addr_len           = 4;
        memcpy(dev->dev_addr, &t->parms.iph.saddr, 4);
        memcpy(dev->broadcast, &t->parms.iph.daddr, 4);
}

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

        tunnel = (struct ip_tunnel*)dev->priv;
        iph = &tunnel->parms.iph;

        ipip6_tunnel_init_gen(dev);

        if (iph->daddr) {
                struct rtable *rt;
                if (!ip_route_output(&rt, iph->daddr, iph->saddr, RT_TOS(iph->tos), tunnel->parms.link)) {
                        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;
}

#ifdef MODULE
static int ipip6_fb_tunnel_open(struct device *dev)
{
        MOD_INC_USE_COUNT;
        return 0;
}

static int ipip6_fb_tunnel_close(struct device *dev)
{
        MOD_DEC_USE_COUNT;
        return 0;
}
#endif

__initfunc(int ipip6_fb_tunnel_init(struct device *dev))
{
        struct iphdr *iph;

        ipip6_tunnel_init_gen(dev);
#ifdef MODULE
        dev->open               = ipip6_fb_tunnel_open;
        dev->stop               = ipip6_fb_tunnel_close;
#endif

        iph = &ipip6_fb_tunnel.parms.iph;
        iph->version            = 4;
        iph->protocol           = IPPROTO_IPV6;
        iph->ihl                = 5;
        iph->ttl                = 64;

        tunnels_wc[0]           = &ipip6_fb_tunnel;
        return 0;
}

static struct inet_protocol sit_protocol = {
        ipip6_rcv,
        ipip6_err,
        0,
        IPPROTO_IPV6,
        0,
        NULL,
        "IPv6"
};

#ifdef MODULE
void sit_cleanup(void)
{
        inet_del_protocol(&sit_protocol);
        unregister_netdevice(&ipip6_fb_tunnel_dev);
}
#endif

__initfunc(int sit_init(void))
{
        printk(KERN_INFO "IPv6 over IPv4 tunneling driver\n");

        ipip6_fb_tunnel_dev.priv = (void*)&ipip6_fb_tunnel;
        ipip6_fb_tunnel_dev.name = ipip6_fb_tunnel.parms.name;
#ifdef MODULE
        register_netdev(&ipip6_fb_tunnel_dev);
#else
        register_netdevice(&ipip6_fb_tunnel_dev);
#endif
        inet_add_protocol(&sit_protocol);
        return 0;
}

---