linux/net/netfilter/xt_TEE.c
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   1/*
   2 *      "TEE" target extension for Xtables
   3 *      Copyright © Sebastian Claßen, 2007
   4 *      Jan Engelhardt, 2007-2010
   5 *
   6 *      based on ipt_ROUTE.c from Cédric de Launois
   7 *      <delaunois@info.ucl.be>
   8 *
   9 *      This program is free software; you can redistribute it and/or
  10 *      modify it under the terms of the GNU General Public License
  11 *      version 2 or later, as published by the Free Software Foundation.
  12 */
  13#include <linux/ip.h>
  14#include <linux/module.h>
  15#include <linux/percpu.h>
  16#include <linux/route.h>
  17#include <linux/skbuff.h>
  18#include <linux/notifier.h>
  19#include <net/checksum.h>
  20#include <net/icmp.h>
  21#include <net/ip.h>
  22#include <net/ipv6.h>
  23#include <net/ip6_route.h>
  24#include <net/route.h>
  25#include <linux/netfilter/x_tables.h>
  26#include <linux/netfilter/xt_TEE.h>
  27
  28#if IS_ENABLED(CONFIG_NF_CONNTRACK)
  29#       define WITH_CONNTRACK 1
  30#       include <net/netfilter/nf_conntrack.h>
  31#endif
  32
  33struct xt_tee_priv {
  34        struct notifier_block   notifier;
  35        struct xt_tee_tginfo    *tginfo;
  36        int                     oif;
  37};
  38
  39static const union nf_inet_addr tee_zero_address;
  40static DEFINE_PER_CPU(bool, tee_active);
  41
  42static struct net *pick_net(struct sk_buff *skb)
  43{
  44#ifdef CONFIG_NET_NS
  45        const struct dst_entry *dst;
  46
  47        if (skb->dev != NULL)
  48                return dev_net(skb->dev);
  49        dst = skb_dst(skb);
  50        if (dst != NULL && dst->dev != NULL)
  51                return dev_net(dst->dev);
  52#endif
  53        return &init_net;
  54}
  55
  56static bool
  57tee_tg_route4(struct sk_buff *skb, const struct xt_tee_tginfo *info)
  58{
  59        const struct iphdr *iph = ip_hdr(skb);
  60        struct net *net = pick_net(skb);
  61        struct rtable *rt;
  62        struct flowi4 fl4;
  63
  64        memset(&fl4, 0, sizeof(fl4));
  65        if (info->priv) {
  66                if (info->priv->oif == -1)
  67                        return false;
  68                fl4.flowi4_oif = info->priv->oif;
  69        }
  70        fl4.daddr = info->gw.ip;
  71        fl4.flowi4_tos = RT_TOS(iph->tos);
  72        fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
  73        fl4.flowi4_flags = FLOWI_FLAG_KNOWN_NH;
  74        rt = ip_route_output_key(net, &fl4);
  75        if (IS_ERR(rt))
  76                return false;
  77
  78        skb_dst_drop(skb);
  79        skb_dst_set(skb, &rt->dst);
  80        skb->dev      = rt->dst.dev;
  81        skb->protocol = htons(ETH_P_IP);
  82        return true;
  83}
  84
  85static unsigned int
  86tee_tg4(struct sk_buff *skb, const struct xt_action_param *par)
  87{
  88        const struct xt_tee_tginfo *info = par->targinfo;
  89        struct iphdr *iph;
  90
  91        if (__this_cpu_read(tee_active))
  92                return XT_CONTINUE;
  93        /*
  94         * Copy the skb, and route the copy. Will later return %XT_CONTINUE for
  95         * the original skb, which should continue on its way as if nothing has
  96         * happened. The copy should be independently delivered to the TEE
  97         * --gateway.
  98         */
  99        skb = pskb_copy(skb, GFP_ATOMIC);
 100        if (skb == NULL)
 101                return XT_CONTINUE;
 102
 103#ifdef WITH_CONNTRACK
 104        /* Avoid counting cloned packets towards the original connection. */
 105        nf_conntrack_put(skb->nfct);
 106        skb->nfct     = &nf_ct_untracked_get()->ct_general;
 107        skb->nfctinfo = IP_CT_NEW;
 108        nf_conntrack_get(skb->nfct);
 109#endif
 110        /*
 111         * If we are in PREROUTING/INPUT, the checksum must be recalculated
 112         * since the length could have changed as a result of defragmentation.
 113         *
 114         * We also decrease the TTL to mitigate potential TEE loops
 115         * between two hosts.
 116         *
 117         * Set %IP_DF so that the original source is notified of a potentially
 118         * decreased MTU on the clone route. IPv6 does this too.
 119         */
 120        iph = ip_hdr(skb);
 121        iph->frag_off |= htons(IP_DF);
 122        if (par->hooknum == NF_INET_PRE_ROUTING ||
 123            par->hooknum == NF_INET_LOCAL_IN)
 124                --iph->ttl;
 125        ip_send_check(iph);
 126
 127        if (tee_tg_route4(skb, info)) {
 128                __this_cpu_write(tee_active, true);
 129                ip_local_out(skb);
 130                __this_cpu_write(tee_active, false);
 131        } else {
 132                kfree_skb(skb);
 133        }
 134        return XT_CONTINUE;
 135}
 136
 137#if IS_ENABLED(CONFIG_IPV6)
 138static bool
 139tee_tg_route6(struct sk_buff *skb, const struct xt_tee_tginfo *info)
 140{
 141        const struct ipv6hdr *iph = ipv6_hdr(skb);
 142        struct net *net = pick_net(skb);
 143        struct dst_entry *dst;
 144        struct flowi6 fl6;
 145
 146        memset(&fl6, 0, sizeof(fl6));
 147        if (info->priv) {
 148                if (info->priv->oif == -1)
 149                        return false;
 150                fl6.flowi6_oif = info->priv->oif;
 151        }
 152        fl6.daddr = info->gw.in6;
 153        fl6.flowlabel = ((iph->flow_lbl[0] & 0xF) << 16) |
 154                           (iph->flow_lbl[1] << 8) | iph->flow_lbl[2];
 155        dst = ip6_route_output(net, NULL, &fl6);
 156        if (dst->error) {
 157                dst_release(dst);
 158                return false;
 159        }
 160        skb_dst_drop(skb);
 161        skb_dst_set(skb, dst);
 162        skb->dev      = dst->dev;
 163        skb->protocol = htons(ETH_P_IPV6);
 164        return true;
 165}
 166
 167static unsigned int
 168tee_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 169{
 170        const struct xt_tee_tginfo *info = par->targinfo;
 171
 172        if (__this_cpu_read(tee_active))
 173                return XT_CONTINUE;
 174        skb = pskb_copy(skb, GFP_ATOMIC);
 175        if (skb == NULL)
 176                return XT_CONTINUE;
 177
 178#ifdef WITH_CONNTRACK
 179        nf_conntrack_put(skb->nfct);
 180        skb->nfct     = &nf_ct_untracked_get()->ct_general;
 181        skb->nfctinfo = IP_CT_NEW;
 182        nf_conntrack_get(skb->nfct);
 183#endif
 184        if (par->hooknum == NF_INET_PRE_ROUTING ||
 185            par->hooknum == NF_INET_LOCAL_IN) {
 186                struct ipv6hdr *iph = ipv6_hdr(skb);
 187                --iph->hop_limit;
 188        }
 189        if (tee_tg_route6(skb, info)) {
 190                __this_cpu_write(tee_active, true);
 191                ip6_local_out(skb);
 192                __this_cpu_write(tee_active, false);
 193        } else {
 194                kfree_skb(skb);
 195        }
 196        return XT_CONTINUE;
 197}
 198#endif
 199
 200static int tee_netdev_event(struct notifier_block *this, unsigned long event,
 201                            void *ptr)
 202{
 203        struct net_device *dev = ptr;
 204        struct xt_tee_priv *priv;
 205
 206        priv = container_of(this, struct xt_tee_priv, notifier);
 207        switch (event) {
 208        case NETDEV_REGISTER:
 209                if (!strcmp(dev->name, priv->tginfo->oif))
 210                        priv->oif = dev->ifindex;
 211                break;
 212        case NETDEV_UNREGISTER:
 213                if (dev->ifindex == priv->oif)
 214                        priv->oif = -1;
 215                break;
 216        case NETDEV_CHANGENAME:
 217                if (!strcmp(dev->name, priv->tginfo->oif))
 218                        priv->oif = dev->ifindex;
 219                else if (dev->ifindex == priv->oif)
 220                        priv->oif = -1;
 221                break;
 222        }
 223
 224        return NOTIFY_DONE;
 225}
 226
 227static int tee_tg_check(const struct xt_tgchk_param *par)
 228{
 229        struct xt_tee_tginfo *info = par->targinfo;
 230        struct xt_tee_priv *priv;
 231
 232        /* 0.0.0.0 and :: not allowed */
 233        if (memcmp(&info->gw, &tee_zero_address,
 234                   sizeof(tee_zero_address)) == 0)
 235                return -EINVAL;
 236
 237        if (info->oif[0]) {
 238                if (info->oif[sizeof(info->oif)-1] != '\0')
 239                        return -EINVAL;
 240
 241                priv = kzalloc(sizeof(*priv), GFP_KERNEL);
 242                if (priv == NULL)
 243                        return -ENOMEM;
 244
 245                priv->tginfo  = info;
 246                priv->oif     = -1;
 247                priv->notifier.notifier_call = tee_netdev_event;
 248                info->priv    = priv;
 249
 250                register_netdevice_notifier(&priv->notifier);
 251        } else
 252                info->priv = NULL;
 253
 254        return 0;
 255}
 256
 257static void tee_tg_destroy(const struct xt_tgdtor_param *par)
 258{
 259        struct xt_tee_tginfo *info = par->targinfo;
 260
 261        if (info->priv) {
 262                unregister_netdevice_notifier(&info->priv->notifier);
 263                kfree(info->priv);
 264        }
 265}
 266
 267static struct xt_target tee_tg_reg[] __read_mostly = {
 268        {
 269                .name       = "TEE",
 270                .revision   = 1,
 271                .family     = NFPROTO_IPV4,
 272                .target     = tee_tg4,
 273                .targetsize = sizeof(struct xt_tee_tginfo),
 274                .checkentry = tee_tg_check,
 275                .destroy    = tee_tg_destroy,
 276                .me         = THIS_MODULE,
 277        },
 278#if IS_ENABLED(CONFIG_IPV6)
 279        {
 280                .name       = "TEE",
 281                .revision   = 1,
 282                .family     = NFPROTO_IPV6,
 283                .target     = tee_tg6,
 284                .targetsize = sizeof(struct xt_tee_tginfo),
 285                .checkentry = tee_tg_check,
 286                .destroy    = tee_tg_destroy,
 287                .me         = THIS_MODULE,
 288        },
 289#endif
 290};
 291
 292static int __init tee_tg_init(void)
 293{
 294        return xt_register_targets(tee_tg_reg, ARRAY_SIZE(tee_tg_reg));
 295}
 296
 297static void __exit tee_tg_exit(void)
 298{
 299        xt_unregister_targets(tee_tg_reg, ARRAY_SIZE(tee_tg_reg));
 300}
 301
 302module_init(tee_tg_init);
 303module_exit(tee_tg_exit);
 304MODULE_AUTHOR("Sebastian Claßen <sebastian.classen@freenet.ag>");
 305MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 306MODULE_DESCRIPTION("Xtables: Reroute packet copy");
 307MODULE_LICENSE("GPL");
 308MODULE_ALIAS("ipt_TEE");
 309MODULE_ALIAS("ip6t_TEE");
 310
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