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         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
  85 static unsigned int
  86 tee_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)
 138 static bool
 139 tee_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         fl6.flowi6_flags = FLOWI_FLAG_KNOWN_NH;
 156         dst = ip6_route_output(net, NULL, &fl6);
 157         if (dst->error) {
 158                 dst_release(dst);
 159                 return false;
 160         }
 161         skb_dst_drop(skb);
 162         skb_dst_set(skb, dst);
 163         skb->dev      = dst->dev;
 164         skb->protocol = htons(ETH_P_IPV6);
 165         return true;
 166 }
 167
 168 static unsigned int
 169 tee_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 170 {
 171         const struct xt_tee_tginfo *info = par->targinfo;
 172
 173         if (__this_cpu_read(tee_active))
 174                 return XT_CONTINUE;
 175         skb = pskb_copy(skb, GFP_ATOMIC);
 176         if (skb == NULL)
 177                 return XT_CONTINUE;
 178
 179 #ifdef WITH_CONNTRACK
 180         nf_conntrack_put(skb->nfct);
 181         skb->nfct     = &nf_ct_untracked_get()->ct_general;
 182         skb->nfctinfo = IP_CT_NEW;
 183         nf_conntrack_get(skb->nfct);
 184 #endif
 185         if (par->hooknum == NF_INET_PRE_ROUTING ||
 186             par->hooknum == NF_INET_LOCAL_IN) {
 187                 struct ipv6hdr *iph = ipv6_hdr(skb);
 188                 --iph->hop_limit;
 189         }
 190         if (tee_tg_route6(skb, info)) {
 191                 __this_cpu_write(tee_active, true);
 192                 ip6_local_out(skb);
 193                 __this_cpu_write(tee_active, false);
 194         } else {
 195                 kfree_skb(skb);
 196         }
 197         return XT_CONTINUE;
 198 }
 199 #endif
 200
 201 static int tee_netdev_event(struct notifier_block *this, unsigned long event,
 202                             void *ptr)
 203 {
 204         struct net_device *dev = netdev_notifier_info_to_dev(ptr);
 205         struct xt_tee_priv *priv;
 206
 207         priv = container_of(this, struct xt_tee_priv, notifier);
 208         switch (event) {
 209         case NETDEV_REGISTER:
 210                 if (!strcmp(dev->name, priv->tginfo->oif))
 211                         priv->oif = dev->ifindex;
 212                 break;
 213         case NETDEV_UNREGISTER:
 214                 if (dev->ifindex == priv->oif)
 215                         priv->oif = -1;
 216                 break;
 217         case NETDEV_CHANGENAME:
 218                 if (!strcmp(dev->name, priv->tginfo->oif))
 219                         priv->oif = dev->ifindex;
 220                 else if (dev->ifindex == priv->oif)
 221                         priv->oif = -1;
 222                 break;
 223         }
 224
 225         return NOTIFY_DONE;
 226 }
 227
 228 static int tee_tg_check(const struct xt_tgchk_param *par)
 229 {
 230         struct xt_tee_tginfo *info = par->targinfo;
 231         struct xt_tee_priv *priv;
 232
 233         /* 0.0.0.0 and :: not allowed */
 234         if (memcmp(&info->gw, &tee_zero_address,
 235                    sizeof(tee_zero_address)) == 0)
 236                 return -EINVAL;
 237
 238         if (info->oif[0]) {
 239                 if (info->oif[sizeof(info->oif)-1] != '\0')
 240                         return -EINVAL;
 241
 242                 priv = kzalloc(sizeof(*priv), GFP_KERNEL);
 243                 if (priv == NULL)
 244                         return -ENOMEM;
 245
 246                 priv->tginfo  = info;
 247                 priv->oif     = -1;
 248                 priv->notifier.notifier_call = tee_netdev_event;
 249                 info->priv    = priv;
 250
 251                 register_netdevice_notifier(&priv->notifier);
 252         } else
 253                 info->priv = NULL;
 254
 255         return 0;
 256 }
 257
 258 static void tee_tg_destroy(const struct xt_tgdtor_param *par)
 259 {
 260         struct xt_tee_tginfo *info = par->targinfo;
 261
 262         if (info->priv) {
 263                 unregister_netdevice_notifier(&info->priv->notifier);
 264                 kfree(info->priv);
 265         }
 266 }
 267
 268 static struct xt_target tee_tg_reg[] __read_mostly = {
 269         {
 270                 .name       = "TEE",
 271                 .revision   = 1,
 272                 .family     = NFPROTO_IPV4,
 273                 .target     = tee_tg4,
 274                 .targetsize = sizeof(struct xt_tee_tginfo),
 275                 .checkentry = tee_tg_check,
 276                 .destroy    = tee_tg_destroy,
 277                 .me         = THIS_MODULE,
 278         },
 279 #if IS_ENABLED(CONFIG_IPV6)
 280         {
 281                 .name       = "TEE",
 282                 .revision   = 1,
 283                 .family     = NFPROTO_IPV6,
 284                 .target     = tee_tg6,
 285                 .targetsize = sizeof(struct xt_tee_tginfo),
 286                 .checkentry = tee_tg_check,
 287                 .destroy    = tee_tg_destroy,
 288                 .me         = THIS_MODULE,
 289         },
 290 #endif
 291 };
 292
 293 static int __init tee_tg_init(void)
 294 {
 295         return xt_register_targets(tee_tg_reg, ARRAY_SIZE(tee_tg_reg));
 296 }
 297
 298 static void __exit tee_tg_exit(void)
 299 {
 300         xt_unregister_targets(tee_tg_reg, ARRAY_SIZE(tee_tg_reg));
 301 }
 302
 303 module_init(tee_tg_init);
 304 module_exit(tee_tg_exit);
 305 MODULE_AUTHOR("Sebastian Claßen <sebastian.classen@freenet.ag>");
 306 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 307 MODULE_DESCRIPTION("Xtables: Reroute packet copy");
 308 MODULE_LICENSE("GPL");
 309 MODULE_ALIAS("ipt_TEE");
 310 MODULE_ALIAS("ip6t_TEE");