net/netfilter/xt_TEE.c

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