Linux 2.6.38-rc8

[mirror_ubuntu-artful-kernel.git] / net / ipv6 / sit.c

/*
 *      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>
 *
 *      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
 * Fred Templin <fred.l.templin@boeing.com>:    isatap 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/net.h>
#include <linux/in6.h>
#include <linux/netdevice.h>
#include <linux/if_arp.h>
#include <linux/icmp.h>
#include <linux/slab.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>
#include <net/net_namespace.h>
#include <net/netns/generic.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_tunnel_init(struct net_device *dev);
static void ipip6_tunnel_setup(struct net_device *dev);
static void ipip6_dev_free(struct net_device *dev);

static int sit_net_id __read_mostly;
struct sit_net {
        struct ip_tunnel __rcu *tunnels_r_l[HASH_SIZE];
        struct ip_tunnel __rcu *tunnels_r[HASH_SIZE];
        struct ip_tunnel __rcu *tunnels_l[HASH_SIZE];
        struct ip_tunnel __rcu *tunnels_wc[1];
        struct ip_tunnel __rcu **tunnels[4];

        struct net_device *fb_tunnel_dev;
};

/*
 * Locking : hash tables are protected by RCU and RTNL
 */

#define for_each_ip_tunnel_rcu(start) \
        for (t = rcu_dereference(start); t; t = rcu_dereference(t->next))

/* often modified stats are per cpu, other are shared (netdev->stats) */
struct pcpu_tstats {
        unsigned long   rx_packets;
        unsigned long   rx_bytes;
        unsigned long   tx_packets;
        unsigned long   tx_bytes;
};

static struct net_device_stats *ipip6_get_stats(struct net_device *dev)
{
        struct pcpu_tstats sum = { 0 };
        int i;

        for_each_possible_cpu(i) {
                const struct pcpu_tstats *tstats = per_cpu_ptr(dev->tstats, i);

                sum.rx_packets += tstats->rx_packets;
                sum.rx_bytes   += tstats->rx_bytes;
                sum.tx_packets += tstats->tx_packets;
                sum.tx_bytes   += tstats->tx_bytes;
        }
        dev->stats.rx_packets = sum.rx_packets;
        dev->stats.rx_bytes   = sum.rx_bytes;
        dev->stats.tx_packets = sum.tx_packets;
        dev->stats.tx_bytes   = sum.tx_bytes;
        return &dev->stats;
}
/*
 * Must be invoked with rcu_read_lock
 */
static struct ip_tunnel * ipip6_tunnel_lookup(struct net *net,
                struct net_device *dev, __be32 remote, __be32 local)
{
        unsigned int h0 = HASH(remote);
        unsigned int h1 = HASH(local);
        struct ip_tunnel *t;
        struct sit_net *sitn = net_generic(net, sit_net_id);

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

static struct ip_tunnel __rcu **__ipip6_bucket(struct sit_net *sitn,
                struct ip_tunnel_parm *parms)
{
        __be32 remote = parms->iph.daddr;
        __be32 local = parms->iph.saddr;
        unsigned int h = 0;
        int prio = 0;

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

static inline struct ip_tunnel __rcu **ipip6_bucket(struct sit_net *sitn,
                struct ip_tunnel *t)
{
        return __ipip6_bucket(sitn, &t->parms);
}

static void ipip6_tunnel_unlink(struct sit_net *sitn, struct ip_tunnel *t)
{
        struct ip_tunnel __rcu **tp;
        struct ip_tunnel *iter;

        for (tp = ipip6_bucket(sitn, t);
             (iter = rtnl_dereference(*tp)) != NULL;
             tp = &iter->next) {
                if (t == iter) {
                        rcu_assign_pointer(*tp, t->next);
                        break;
                }
        }
}

static void ipip6_tunnel_link(struct sit_net *sitn, struct ip_tunnel *t)
{
        struct ip_tunnel __rcu **tp = ipip6_bucket(sitn, t);

        rcu_assign_pointer(t->next, rtnl_dereference(*tp));
        rcu_assign_pointer(*tp, t);
}

static void ipip6_tunnel_clone_6rd(struct net_device *dev, struct sit_net *sitn)
{
#ifdef CONFIG_IPV6_SIT_6RD
        struct ip_tunnel *t = netdev_priv(dev);

        if (t->dev == sitn->fb_tunnel_dev) {
                ipv6_addr_set(&t->ip6rd.prefix, htonl(0x20020000), 0, 0, 0);
                t->ip6rd.relay_prefix = 0;
                t->ip6rd.prefixlen = 16;
                t->ip6rd.relay_prefixlen = 0;
        } else {
                struct ip_tunnel *t0 = netdev_priv(sitn->fb_tunnel_dev);
                memcpy(&t->ip6rd, &t0->ip6rd, sizeof(t->ip6rd));
        }
#endif
}

static struct ip_tunnel *ipip6_tunnel_locate(struct net *net,
                struct ip_tunnel_parm *parms, int create)
{
        __be32 remote = parms->iph.daddr;
        __be32 local = parms->iph.saddr;
        struct ip_tunnel *t, *nt;
        struct ip_tunnel __rcu **tp;
        struct net_device *dev;
        char name[IFNAMSIZ];
        struct sit_net *sitn = net_generic(net, sit_net_id);

        for (tp = __ipip6_bucket(sitn, parms);
            (t = rtnl_dereference(*tp)) != NULL;
             tp = &t->next) {
                if (local == t->parms.iph.saddr &&
                    remote == t->parms.iph.daddr &&
                    parms->link == t->parms.link) {
                        if (create)
                                return NULL;
                        else
                                return t;
                }
        }
        if (!create)
                goto failed;

        if (parms->name[0])
                strlcpy(name, parms->name, IFNAMSIZ);
        else
                strcpy(name, "sit%d");

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

        dev_net_set(dev, net);

        if (strchr(name, '%')) {
                if (dev_alloc_name(dev, name) < 0)
                        goto failed_free;
        }

        nt = netdev_priv(dev);

        nt->parms = *parms;
        if (ipip6_tunnel_init(dev) < 0)
                goto failed_free;
        ipip6_tunnel_clone_6rd(dev, sitn);

        if (parms->i_flags & SIT_ISATAP)
                dev->priv_flags |= IFF_ISATAP;

        if (register_netdevice(dev) < 0)
                goto failed_free;

        dev_hold(dev);

        ipip6_tunnel_link(sitn, nt);
        return nt;

failed_free:
        ipip6_dev_free(dev);
failed:
        return NULL;
}

#define for_each_prl_rcu(start)                 \
        for (prl = rcu_dereference(start);      \
             prl;                               \
             prl = rcu_dereference(prl->next))

static struct ip_tunnel_prl_entry *
__ipip6_tunnel_locate_prl(struct ip_tunnel *t, __be32 addr)
{
        struct ip_tunnel_prl_entry *prl;

        for_each_prl_rcu(t->prl)
                if (prl->addr == addr)
                        break;
        return prl;

}

static int ipip6_tunnel_get_prl(struct ip_tunnel *t,
                                struct ip_tunnel_prl __user *a)
{
        struct ip_tunnel_prl kprl, *kp;
        struct ip_tunnel_prl_entry *prl;
        unsigned int cmax, c = 0, ca, len;
        int ret = 0;

        if (copy_from_user(&kprl, a, sizeof(kprl)))
                return -EFAULT;
        cmax = kprl.datalen / sizeof(kprl);
        if (cmax > 1 && kprl.addr != htonl(INADDR_ANY))
                cmax = 1;

        /* For simple GET or for root users,
         * we try harder to allocate.
         */
        kp = (cmax <= 1 || capable(CAP_NET_ADMIN)) ?
                kcalloc(cmax, sizeof(*kp), GFP_KERNEL) :
                NULL;

        rcu_read_lock();

        ca = t->prl_count < cmax ? t->prl_count : cmax;

        if (!kp) {
                /* We don't try hard to allocate much memory for
                 * non-root users.
                 * For root users, retry allocating enough memory for
                 * the answer.
                 */
                kp = kcalloc(ca, sizeof(*kp), GFP_ATOMIC);
                if (!kp) {
                        ret = -ENOMEM;
                        goto out;
                }
        }

        c = 0;
        for_each_prl_rcu(t->prl) {
                if (c >= cmax)
                        break;
                if (kprl.addr != htonl(INADDR_ANY) && prl->addr != kprl.addr)
                        continue;
                kp[c].addr = prl->addr;
                kp[c].flags = prl->flags;
                c++;
                if (kprl.addr != htonl(INADDR_ANY))
                        break;
        }
out:
        rcu_read_unlock();

        len = sizeof(*kp) * c;
        ret = 0;
        if ((len && copy_to_user(a + 1, kp, len)) || put_user(len, &a->datalen))
                ret = -EFAULT;

        kfree(kp);

        return ret;
}

static int
ipip6_tunnel_add_prl(struct ip_tunnel *t, struct ip_tunnel_prl *a, int chg)
{
        struct ip_tunnel_prl_entry *p;
        int err = 0;

        if (a->addr == htonl(INADDR_ANY))
                return -EINVAL;

        ASSERT_RTNL();

        for (p = rtnl_dereference(t->prl); p; p = rtnl_dereference(p->next)) {
                if (p->addr == a->addr) {
                        if (chg) {
                                p->flags = a->flags;
                                goto out;
                        }
                        err = -EEXIST;
                        goto out;
                }
        }

        if (chg) {
                err = -ENXIO;
                goto out;
        }

        p = kzalloc(sizeof(struct ip_tunnel_prl_entry), GFP_KERNEL);
        if (!p) {
                err = -ENOBUFS;
                goto out;
        }

        p->next = t->prl;
        p->addr = a->addr;
        p->flags = a->flags;
        t->prl_count++;
        rcu_assign_pointer(t->prl, p);
out:
        return err;
}

static void prl_entry_destroy_rcu(struct rcu_head *head)
{
        kfree(container_of(head, struct ip_tunnel_prl_entry, rcu_head));
}

static void prl_list_destroy_rcu(struct rcu_head *head)
{
        struct ip_tunnel_prl_entry *p, *n;

        p = container_of(head, struct ip_tunnel_prl_entry, rcu_head);
        do {
                n = p->next;
                kfree(p);
                p = n;
        } while (p);
}

static int
ipip6_tunnel_del_prl(struct ip_tunnel *t, struct ip_tunnel_prl *a)
{
        struct ip_tunnel_prl_entry *x, **p;
        int err = 0;

        ASSERT_RTNL();

        if (a && a->addr != htonl(INADDR_ANY)) {
                for (p = &t->prl; *p; p = &(*p)->next) {
                        if ((*p)->addr == a->addr) {
                                x = *p;
                                *p = x->next;
                                call_rcu(&x->rcu_head, prl_entry_destroy_rcu);
                                t->prl_count--;
                                goto out;
                        }
                }
                err = -ENXIO;
        } else {
                if (t->prl) {
                        t->prl_count = 0;
                        x = t->prl;
                        call_rcu(&x->rcu_head, prl_list_destroy_rcu);
                        t->prl = NULL;
                }
        }
out:
        return err;
}

static int
isatap_chksrc(struct sk_buff *skb, struct iphdr *iph, struct ip_tunnel *t)
{
        struct ip_tunnel_prl_entry *p;
        int ok = 1;

        rcu_read_lock();
        p = __ipip6_tunnel_locate_prl(t, iph->saddr);
        if (p) {
                if (p->flags & PRL_DEFAULT)
                        skb->ndisc_nodetype = NDISC_NODETYPE_DEFAULT;
                else
                        skb->ndisc_nodetype = NDISC_NODETYPE_NODEFAULT;
        } else {
                struct in6_addr *addr6 = &ipv6_hdr(skb)->saddr;
                if (ipv6_addr_is_isatap(addr6) &&
                    (addr6->s6_addr32[3] == iph->saddr) &&
                    ipv6_chk_prefix(addr6, t->dev))
                        skb->ndisc_nodetype = NDISC_NODETYPE_HOST;
                else
                        ok = 0;
        }
        rcu_read_unlock();
        return ok;
}

static void ipip6_tunnel_uninit(struct net_device *dev)
{
        struct net *net = dev_net(dev);
        struct sit_net *sitn = net_generic(net, sit_net_id);

        if (dev == sitn->fb_tunnel_dev) {
                rcu_assign_pointer(sitn->tunnels_wc[0], NULL);
        } else {
                ipip6_tunnel_unlink(sitn, netdev_priv(dev));
                ipip6_tunnel_del_prl(netdev_priv(dev), NULL);
        }
        dev_put(dev);
}


static int ipip6_err(struct sk_buff *skb, u32 info)
{

/* 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;
        const int type = icmp_hdr(skb)->type;
        const int code = icmp_hdr(skb)->code;
        struct ip_tunnel *t;
        int err;

        switch (type) {
        default:
        case ICMP_PARAMETERPROB:
                return 0;

        case ICMP_DEST_UNREACH:
                switch (code) {
                case ICMP_SR_FAILED:
                case ICMP_PORT_UNREACH:
                        /* Impossible event. */
                        return 0;
                case ICMP_FRAG_NEEDED:
                        /* Soft state for pmtu is maintained by IP core. */
                        return 0;
                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 0;
                break;
        }

        err = -ENOENT;

        rcu_read_lock();
        t = ipip6_tunnel_lookup(dev_net(skb->dev),
                                skb->dev,
                                iph->daddr,
                                iph->saddr);
        if (t == NULL || t->parms.iph.daddr == 0)
                goto out;

        err = 0;
        if (t->parms.iph.ttl == 0 && type == ICMP_TIME_EXCEEDED)
                goto out;

        if (time_before(jiffies, t->err_time + IPTUNNEL_ERR_TIMEO))
                t->err_count++;
        else
                t->err_count = 1;
        t->err_time = jiffies;
out:
        rcu_read_unlock();
        return err;
}

static inline void ipip6_ecn_decapsulate(struct iphdr *iph, struct sk_buff *skb)
{
        if (INET_ECN_is_ce(iph->tos))
                IP6_ECN_set_ce(ipv6_hdr(skb));
}

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 = ip_hdr(skb);

        rcu_read_lock();
        tunnel = ipip6_tunnel_lookup(dev_net(skb->dev), skb->dev,
                                     iph->saddr, iph->daddr);
        if (tunnel != NULL) {
                struct pcpu_tstats *tstats;

                secpath_reset(skb);
                skb->mac_header = skb->network_header;
                skb_reset_network_header(skb);
                IPCB(skb)->flags = 0;
                skb->protocol = htons(ETH_P_IPV6);
                skb->pkt_type = PACKET_HOST;

                if ((tunnel->dev->priv_flags & IFF_ISATAP) &&
                    !isatap_chksrc(skb, iph, tunnel)) {
                        tunnel->dev->stats.rx_errors++;
                        rcu_read_unlock();
                        kfree_skb(skb);
                        return 0;
                }

                tstats = this_cpu_ptr(tunnel->dev->tstats);
                tstats->rx_packets++;
                tstats->rx_bytes += skb->len;

                __skb_tunnel_rx(skb, tunnel->dev);

                ipip6_ecn_decapsulate(iph, skb);

                netif_rx(skb);

                rcu_read_unlock();
                return 0;
        }

        /* no tunnel matched,  let upstream know, ipsec may handle it */
        rcu_read_unlock();
        return 1;
out:
        kfree_skb(skb);
        return 0;
}

/*
 * Returns the embedded IPv4 address if the IPv6 address
 * comes from 6rd / 6to4 (RFC 3056) addr space.
 */
static inline
__be32 try_6rd(struct in6_addr *v6dst, struct ip_tunnel *tunnel)
{
        __be32 dst = 0;

#ifdef CONFIG_IPV6_SIT_6RD
        if (ipv6_prefix_equal(v6dst, &tunnel->ip6rd.prefix,
                              tunnel->ip6rd.prefixlen)) {
                unsigned int pbw0, pbi0;
                int pbi1;
                u32 d;

                pbw0 = tunnel->ip6rd.prefixlen >> 5;
                pbi0 = tunnel->ip6rd.prefixlen & 0x1f;

                d = (ntohl(v6dst->s6_addr32[pbw0]) << pbi0) >>
                    tunnel->ip6rd.relay_prefixlen;

                pbi1 = pbi0 - tunnel->ip6rd.relay_prefixlen;
                if (pbi1 > 0)
                        d |= ntohl(v6dst->s6_addr32[pbw0 + 1]) >>
                             (32 - pbi1);

                dst = tunnel->ip6rd.relay_prefix | htonl(d);
        }
#else
        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);
        }
#endif
        return dst;
}

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

static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
                                     struct net_device *dev)
{
        struct ip_tunnel *tunnel = netdev_priv(dev);
        struct pcpu_tstats *tstats;
        struct iphdr  *tiph = &tunnel->parms.iph;
        struct ipv6hdr *iph6 = ipv6_hdr(skb);
        u8     tos = tunnel->parms.iph.tos;
        __be16 df = tiph->frag_off;
        struct rtable *rt;                      /* Route to the other host */
        struct net_device *tdev;                /* Device to other host */
        struct iphdr  *iph;                     /* Our new IP header */
        unsigned int max_headroom;              /* The extra header space needed */
        __be32 dst = tiph->daddr;
        int    mtu;
        struct in6_addr *addr6;
        int addr_type;

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

        /* ISATAP (RFC4214) - must come before 6to4 */
        if (dev->priv_flags & IFF_ISATAP) {
                struct neighbour *neigh = NULL;

                if (skb_dst(skb))
                        neigh = skb_dst(skb)->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_UNICAST) &&
                     ipv6_addr_is_isatap(addr6))
                        dst = addr6->s6_addr32[3];
                else
                        goto tx_error;
        }

        if (!dst)
                dst = try_6rd(&iph6->daddr, tunnel);

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

                if (skb_dst(skb))
                        neigh = skb_dst(skb)->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 = &ipv6_hdr(skb)->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 = { .fl4_dst = dst,
                                    .fl4_src = tiph->saddr,
                                    .fl4_tos = RT_TOS(tos),
                                    .oif = tunnel->parms.link,
                                    .proto = IPPROTO_IPV6 };
                if (ip_route_output_key(dev_net(dev), &rt, &fl)) {
                        dev->stats.tx_carrier_errors++;
                        goto tx_error_icmp;
                }
        }
        if (rt->rt_type != RTN_UNICAST) {
                ip_rt_put(rt);
                dev->stats.tx_carrier_errors++;
                goto tx_error_icmp;
        }
        tdev = rt->dst.dev;

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

        if (df) {
                mtu = dst_mtu(&rt->dst) - sizeof(struct iphdr);

                if (mtu < 68) {
                        dev->stats.collisions++;
                        ip_rt_put(rt);
                        goto tx_error;
                }

                if (mtu < IPV6_MIN_MTU) {
                        mtu = IPV6_MIN_MTU;
                        df = 0;
                }

                if (tunnel->parms.iph.daddr && skb_dst(skb))
                        skb_dst(skb)->ops->update_pmtu(skb_dst(skb), mtu);

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

        if (tunnel->err_count > 0) {
                if (time_before(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_shared(skb) ||
            (skb_cloned(skb) && !skb_clone_writable(skb, 0))) {
                struct sk_buff *new_skb = skb_realloc_headroom(skb, max_headroom);
                if (!new_skb) {
                        ip_rt_put(rt);
                        dev->stats.tx_dropped++;
                        dev_kfree_skb(skb);
                        return NETDEV_TX_OK;
                }
                if (skb->sk)
                        skb_set_owner_w(new_skb, skb->sk);
                dev_kfree_skb(skb);
                skb = new_skb;
                iph6 = ipv6_hdr(skb);
        }

        skb->transport_header = skb->network_header;
        skb_push(skb, sizeof(struct iphdr));
        skb_reset_network_header(skb);
        memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
        IPCB(skb)->flags = 0;
        skb_dst_drop(skb);
        skb_dst_set(skb, &rt->dst);

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

        iph                     =       ip_hdr(skb);
        iph->version            =       4;
        iph->ihl                =       sizeof(struct iphdr)>>2;
        iph->frag_off           =       df;
        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);
        tstats = this_cpu_ptr(dev->tstats);
        __IPTUNNEL_XMIT(tstats, &dev->stats);
        return NETDEV_TX_OK;

tx_error_icmp:
        dst_link_failure(skb);
tx_error:
        dev->stats.tx_errors++;
        dev_kfree_skb(skb);
        return NETDEV_TX_OK;
}

static void ipip6_tunnel_bind_dev(struct net_device *dev)
{
        struct net_device *tdev = NULL;
        struct ip_tunnel *tunnel;
        struct iphdr *iph;

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

        if (iph->daddr) {
                struct flowi fl = { .fl4_dst = iph->daddr,
                                    .fl4_src = iph->saddr,
                                    .fl4_tos = RT_TOS(iph->tos),
                                    .oif = tunnel->parms.link,
                                    .proto = IPPROTO_IPV6 };
                struct rtable *rt;
                if (!ip_route_output_key(dev_net(dev), &rt, &fl)) {
                        tdev = rt->dst.dev;
                        ip_rt_put(rt);
                }
                dev->flags |= IFF_POINTOPOINT;
        }

        if (!tdev && tunnel->parms.link)
                tdev = __dev_get_by_index(dev_net(dev), 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;
}

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_prl prl;
        struct ip_tunnel *t;
        struct net *net = dev_net(dev);
        struct sit_net *sitn = net_generic(net, sit_net_id);
#ifdef CONFIG_IPV6_SIT_6RD
        struct ip_tunnel_6rd ip6rd;
#endif

        switch (cmd) {
        case SIOCGETTUNNEL:
#ifdef CONFIG_IPV6_SIT_6RD
        case SIOCGET6RD:
#endif
                t = NULL;
                if (dev == sitn->fb_tunnel_dev) {
                        if (copy_from_user(&p, ifr->ifr_ifru.ifru_data, sizeof(p))) {
                                err = -EFAULT;
                                break;
                        }
                        t = ipip6_tunnel_locate(net, &p, 0);
                }
                if (t == NULL)
                        t = netdev_priv(dev);

                err = -EFAULT;
                if (cmd == SIOCGETTUNNEL) {
                        memcpy(&p, &t->parms, sizeof(p));
                        if (copy_to_user(ifr->ifr_ifru.ifru_data, &p,
                                         sizeof(p)))
                                goto done;
#ifdef CONFIG_IPV6_SIT_6RD
                } else {
                        ipv6_addr_copy(&ip6rd.prefix, &t->ip6rd.prefix);
                        ip6rd.relay_prefix = t->ip6rd.relay_prefix;
                        ip6rd.prefixlen = t->ip6rd.prefixlen;
                        ip6rd.relay_prefixlen = t->ip6rd.relay_prefixlen;
                        if (copy_to_user(ifr->ifr_ifru.ifru_data, &ip6rd,
                                         sizeof(ip6rd)))
                                goto done;
#endif
                }
                err = 0;
                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(net, &p, cmd == SIOCADDTUNNEL);

                if (dev != sitn->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(sitn, t);
                                synchronize_net();
                                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(sitn, 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 (t->parms.link != p.link) {
                                        t->parms.link = p.link;
                                        ipip6_tunnel_bind_dev(dev);
                                        netdev_state_change(dev);
                                }
                        }
                        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 == sitn->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(net, &p, 0)) == NULL)
                                goto done;
                        err = -EPERM;
                        if (t == netdev_priv(sitn->fb_tunnel_dev))
                                goto done;
                        dev = t->dev;
                }
                unregister_netdevice(dev);
                err = 0;
                break;

        case SIOCGETPRL:
                err = -EINVAL;
                if (dev == sitn->fb_tunnel_dev)
                        goto done;
                err = -ENOENT;
                if (!(t = netdev_priv(dev)))
                        goto done;
                err = ipip6_tunnel_get_prl(t, ifr->ifr_ifru.ifru_data);
                break;

        case SIOCADDPRL:
        case SIOCDELPRL:
        case SIOCCHGPRL:
                err = -EPERM;
                if (!capable(CAP_NET_ADMIN))
                        goto done;
                err = -EINVAL;
                if (dev == sitn->fb_tunnel_dev)
                        goto done;
                err = -EFAULT;
                if (copy_from_user(&prl, ifr->ifr_ifru.ifru_data, sizeof(prl)))
                        goto done;
                err = -ENOENT;
                if (!(t = netdev_priv(dev)))
                        goto done;

                switch (cmd) {
                case SIOCDELPRL:
                        err = ipip6_tunnel_del_prl(t, &prl);
                        break;
                case SIOCADDPRL:
                case SIOCCHGPRL:
                        err = ipip6_tunnel_add_prl(t, &prl, cmd == SIOCCHGPRL);
                        break;
                }
                netdev_state_change(dev);
                break;

#ifdef CONFIG_IPV6_SIT_6RD
        case SIOCADD6RD:
        case SIOCCHG6RD:
        case SIOCDEL6RD:
                err = -EPERM;
                if (!capable(CAP_NET_ADMIN))
                        goto done;

                err = -EFAULT;
                if (copy_from_user(&ip6rd, ifr->ifr_ifru.ifru_data,
                                   sizeof(ip6rd)))
                        goto done;

                t = netdev_priv(dev);

                if (cmd != SIOCDEL6RD) {
                        struct in6_addr prefix;
                        __be32 relay_prefix;

                        err = -EINVAL;
                        if (ip6rd.relay_prefixlen > 32 ||
                            ip6rd.prefixlen + (32 - ip6rd.relay_prefixlen) > 64)
                                goto done;

                        ipv6_addr_prefix(&prefix, &ip6rd.prefix,
                                         ip6rd.prefixlen);
                        if (!ipv6_addr_equal(&prefix, &ip6rd.prefix))
                                goto done;
                        if (ip6rd.relay_prefixlen)
                                relay_prefix = ip6rd.relay_prefix &
                                               htonl(0xffffffffUL <<
                                                     (32 - ip6rd.relay_prefixlen));
                        else
                                relay_prefix = 0;
                        if (relay_prefix != ip6rd.relay_prefix)
                                goto done;

                        ipv6_addr_copy(&t->ip6rd.prefix, &prefix);
                        t->ip6rd.relay_prefix = relay_prefix;
                        t->ip6rd.prefixlen = ip6rd.prefixlen;
                        t->ip6rd.relay_prefixlen = ip6rd.relay_prefixlen;
                } else
                        ipip6_tunnel_clone_6rd(dev, sitn);

                err = 0;
                break;
#endif

        default:
                err = -EINVAL;
        }

done:
        return err;
}

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 const struct net_device_ops ipip6_netdev_ops = {
        .ndo_uninit     = ipip6_tunnel_uninit,
        .ndo_start_xmit = ipip6_tunnel_xmit,
        .ndo_do_ioctl   = ipip6_tunnel_ioctl,
        .ndo_change_mtu = ipip6_tunnel_change_mtu,
        .ndo_get_stats  = ipip6_get_stats,
};

static void ipip6_dev_free(struct net_device *dev)
{
        free_percpu(dev->tstats);
        free_netdev(dev);
}

static void ipip6_tunnel_setup(struct net_device *dev)
{
        dev->netdev_ops         = &ipip6_netdev_ops;
        dev->destructor         = ipip6_dev_free;

        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->priv_flags        &= ~IFF_XMIT_DST_RELEASE;
        dev->iflink             = 0;
        dev->addr_len           = 4;
        dev->features           |= NETIF_F_NETNS_LOCAL;
        dev->features           |= NETIF_F_LLTX;
}

static int ipip6_tunnel_init(struct net_device *dev)
{
        struct ip_tunnel *tunnel = netdev_priv(dev);

        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);

        ipip6_tunnel_bind_dev(dev);
        dev->tstats = alloc_percpu(struct pcpu_tstats);
        if (!dev->tstats)
                return -ENOMEM;

        return 0;
}

static int __net_init ipip6_fb_tunnel_init(struct net_device *dev)
{
        struct ip_tunnel *tunnel = netdev_priv(dev);
        struct iphdr *iph = &tunnel->parms.iph;
        struct net *net = dev_net(dev);
        struct sit_net *sitn = net_generic(net, sit_net_id);

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

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

        dev->tstats = alloc_percpu(struct pcpu_tstats);
        if (!dev->tstats)
                return -ENOMEM;
        dev_hold(dev);
        sitn->tunnels_wc[0]     = tunnel;
        return 0;
}

static struct xfrm_tunnel sit_handler __read_mostly = {
        .handler        =       ipip6_rcv,
        .err_handler    =       ipip6_err,
        .priority       =       1,
};

static void __net_exit sit_destroy_tunnels(struct sit_net *sitn, struct list_head *head)
{
        int prio;

        for (prio = 1; prio < 4; prio++) {
                int h;
                for (h = 0; h < HASH_SIZE; h++) {
                        struct ip_tunnel *t = sitn->tunnels[prio][h];

                        while (t != NULL) {
                                unregister_netdevice_queue(t->dev, head);
                                t = t->next;
                        }
                }
        }
}

static int __net_init sit_init_net(struct net *net)
{
        struct sit_net *sitn = net_generic(net, sit_net_id);
        int err;

        sitn->tunnels[0] = sitn->tunnels_wc;
        sitn->tunnels[1] = sitn->tunnels_l;
        sitn->tunnels[2] = sitn->tunnels_r;
        sitn->tunnels[3] = sitn->tunnels_r_l;

        sitn->fb_tunnel_dev = alloc_netdev(sizeof(struct ip_tunnel), "sit0",
                                           ipip6_tunnel_setup);
        if (!sitn->fb_tunnel_dev) {
                err = -ENOMEM;
                goto err_alloc_dev;
        }
        dev_net_set(sitn->fb_tunnel_dev, net);

        err = ipip6_fb_tunnel_init(sitn->fb_tunnel_dev);
        if (err)
                goto err_dev_free;

        ipip6_tunnel_clone_6rd(sitn->fb_tunnel_dev, sitn);

        if ((err = register_netdev(sitn->fb_tunnel_dev)))
                goto err_reg_dev;

        return 0;

err_reg_dev:
        dev_put(sitn->fb_tunnel_dev);
err_dev_free:
        ipip6_dev_free(sitn->fb_tunnel_dev);
err_alloc_dev:
        return err;
}

static void __net_exit sit_exit_net(struct net *net)
{
        struct sit_net *sitn = net_generic(net, sit_net_id);
        LIST_HEAD(list);

        rtnl_lock();
        sit_destroy_tunnels(sitn, &list);
        unregister_netdevice_queue(sitn->fb_tunnel_dev, &list);
        unregister_netdevice_many(&list);
        rtnl_unlock();
}

static struct pernet_operations sit_net_ops = {
        .init = sit_init_net,
        .exit = sit_exit_net,
        .id   = &sit_net_id,
        .size = sizeof(struct sit_net),
};

static void __exit sit_cleanup(void)
{
        xfrm4_tunnel_deregister(&sit_handler, AF_INET6);

        unregister_pernet_device(&sit_net_ops);
        rcu_barrier(); /* Wait for completion of call_rcu()'s */
}

static int __init sit_init(void)
{
        int err;

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

        err = register_pernet_device(&sit_net_ops);
        if (err < 0)
                return err;
        err = xfrm4_tunnel_register(&sit_handler, AF_INET6);
        if (err < 0) {
                unregister_pernet_device(&sit_net_ops);
                printk(KERN_INFO "sit init: Can't add protocol\n");
        }
        return err;
}

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