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/route.h>
  16 #include <linux/skbuff.h>
  17 #include <net/checksum.h>
  18 #include <net/icmp.h>
  19 #include <net/ip.h>
  20 #include <net/ipv6.h>
  21 #include <net/ip6_route.h>
  22 #include <net/route.h>
  23 #include <linux/netfilter/x_tables.h>
  24 #include <linux/netfilter/xt_TEE.h>
  25
  26 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
  27 #       define WITH_CONNTRACK 1
  28 #       include <net/netfilter/nf_conntrack.h>
  29 #endif
  30 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
  31 #       define WITH_IPV6 1
  32 #endif
  33
  34 static const union nf_inet_addr tee_zero_address;
  35
  36 static struct net *pick_net(struct sk_buff *skb)
  37 {
  38 #ifdef CONFIG_NET_NS
  39         const struct dst_entry *dst;
  40
  41         if (skb->dev != NULL)
  42                 return dev_net(skb->dev);
  43         dst = skb_dst(skb);
  44         if (dst != NULL && dst->dev != NULL)
  45                 return dev_net(dst->dev);
  46 #endif
  47         return &init_net;
  48 }
  49
  50 static bool tee_tg_route_oif(struct flowi *f, struct net *net,
  51                              const struct xt_tee_tginfo *info)
  52 {
  53         const struct net_device *dev;
  54
  55         if (*info->oif != '\0')
  56                 return true;
  57         dev = dev_get_by_name(net, info->oif);
  58         if (dev == NULL)
  59                 return false;
  60         f->oif = dev->ifindex;
  61         return true;
  62 }
  63
  64 static bool
  65 tee_tg_route4(struct sk_buff *skb, const struct xt_tee_tginfo *info)
  66 {
  67         const struct iphdr *iph = ip_hdr(skb);
  68         struct net *net = pick_net(skb);
  69         struct rtable *rt;
  70         struct flowi fl;
  71
  72         memset(&fl, 0, sizeof(fl));
  73         if (!tee_tg_route_oif(&fl, net, info))
  74                 return false;
  75         fl.nl_u.ip4_u.daddr = info->gw.ip;
  76         fl.nl_u.ip4_u.tos   = RT_TOS(iph->tos);
  77         fl.nl_u.ip4_u.scope = RT_SCOPE_UNIVERSE;
  78         if (ip_route_output_key(net, &rt, &fl) != 0)
  79                 return false;
  80
  81         dst_release(skb_dst(skb));
  82         skb_dst_set(skb, &rt->u.dst);
  83         skb->dev      = rt->u.dst.dev;
  84         skb->protocol = htons(ETH_P_IP);
  85         return true;
  86 }
  87
  88 static unsigned int
  89 tee_tg4(struct sk_buff *skb, const struct xt_target_param *par)
  90 {
  91         const struct xt_tee_tginfo *info = par->targinfo;
  92         struct iphdr *iph;
  93
  94         /*
  95          * Copy the skb, and route the copy. Will later return %XT_CONTINUE for
  96          * the original skb, which should continue on its way as if nothing has
  97          * happened. The copy should be independently delivered to the TEE
  98          * --gateway.
  99          */
 100         skb = pskb_copy(skb, GFP_ATOMIC);
 101         if (skb == NULL)
 102                 return XT_CONTINUE;
 103
 104 #ifdef WITH_CONNTRACK
 105         /* Avoid counting cloned packets towards the original connection. */
 106         nf_conntrack_put(skb->nfct);
 107         skb->nfct     = &nf_conntrack_untracked.ct_general;
 108         skb->nfctinfo = IP_CT_NEW;
 109         nf_conntrack_get(skb->nfct);
 110 #endif
 111         /*
 112          * If we are in PREROUTING/INPUT, the checksum must be recalculated
 113          * since the length could have changed as a result of defragmentation.
 114          *
 115          * We also decrease the TTL to mitigate potential TEE loops
 116          * between two hosts.
 117          *
 118          * Set %IP_DF so that the original source is notified of a potentially
 119          * decreased MTU on the clone route. IPv6 does this too.
 120          */
 121         iph = ip_hdr(skb);
 122         iph->frag_off |= htons(IP_DF);
 123         if (par->hooknum == NF_INET_PRE_ROUTING ||
 124             par->hooknum == NF_INET_LOCAL_IN)
 125                 --iph->ttl;
 126         ip_send_check(iph);
 127
 128         /*
 129          * Xtables is not reentrant currently, so a choice has to be made:
 130          * 1. return absolute verdict for the original and let the cloned
 131          *    packet travel through the chains
 132          * 2. let the original continue travelling and not pass the clone
 133          *    to Xtables.
 134          * #2 is chosen. Normally, we would use ip_local_out for the clone.
 135          * Because iph->check is already correct and we don't pass it to
 136          * Xtables anyway, a shortcut to dst_output [forwards to ip_output] can
 137          * be taken. %IPSKB_REROUTED needs to be set so that ip_output does not
 138          * invoke POSTROUTING on the cloned packet.
 139          */
 140         IPCB(skb)->flags |= IPSKB_REROUTED;
 141         if (tee_tg_route4(skb, info))
 142                 ip_output(skb);
 143         else
 144                 kfree_skb(skb);
 145
 146         return XT_CONTINUE;
 147 }
 148
 149 #ifdef WITH_IPV6
 150 static bool
 151 tee_tg_route6(struct sk_buff *skb, const struct xt_tee_tginfo *info)
 152 {
 153         const struct ipv6hdr *iph = ipv6_hdr(skb);
 154         struct net *net = pick_net(skb);
 155         struct dst_entry *dst;
 156         struct flowi fl;
 157
 158         memset(&fl, 0, sizeof(fl));
 159         if (!tee_tg_route_oif(&fl, net, info))
 160                 return false;
 161         fl.nl_u.ip6_u.daddr = info->gw.in6;
 162         fl.nl_u.ip6_u.flowlabel = ((iph->flow_lbl[0] & 0xF) << 16) |
 163                                   (iph->flow_lbl[1] << 8) | iph->flow_lbl[2];
 164         dst = ip6_route_output(net, NULL, &fl);
 165         if (dst == NULL)
 166                 return false;
 167
 168         dst_release(skb_dst(skb));
 169         skb_dst_set(skb, dst);
 170         skb->dev      = dst->dev;
 171         skb->protocol = htons(ETH_P_IPV6);
 172         return true;
 173 }
 174
 175 static unsigned int
 176 tee_tg6(struct sk_buff *skb, const struct xt_target_param *par)
 177 {
 178         const struct xt_tee_tginfo *info = par->targinfo;
 179
 180         skb = pskb_copy(skb, GFP_ATOMIC);
 181         if (skb == NULL)
 182                 return XT_CONTINUE;
 183
 184 #ifdef WITH_CONNTRACK
 185         nf_conntrack_put(skb->nfct);
 186         skb->nfct     = &nf_conntrack_untracked.ct_general;
 187         skb->nfctinfo = IP_CT_NEW;
 188         nf_conntrack_get(skb->nfct);
 189 #endif
 190         if (par->hooknum == NF_INET_PRE_ROUTING ||
 191             par->hooknum == NF_INET_LOCAL_IN) {
 192                 struct ipv6hdr *iph = ipv6_hdr(skb);
 193                 --iph->hop_limit;
 194         }
 195         IP6CB(skb)->flags |= IP6SKB_REROUTED;
 196         if (tee_tg_route6(skb, info))
 197                 ip6_output(skb);
 198         else
 199                 kfree_skb(skb);
 200
 201         return XT_CONTINUE;
 202 }
 203 #endif /* WITH_IPV6 */
 204
 205 static int tee_tg_check(const struct xt_tgchk_param *par)
 206 {
 207         const struct xt_tee_tginfo *info = par->targinfo;
 208
 209         if (info->oif[sizeof(info->oif)-1] != '\0')
 210                 return -EINVAL;
 211         /* 0.0.0.0 and :: not allowed */
 212         return (memcmp(&info->gw, &tee_zero_address,
 213                sizeof(tee_zero_address)) == 0) ? -EINVAL : 0;
 214 }
 215
 216 static struct xt_target tee_tg_reg[] __read_mostly = {
 217         {
 218                 .name       = "TEE",
 219                 .revision   = 1,
 220                 .family     = NFPROTO_IPV4,
 221                 .target     = tee_tg4,
 222                 .targetsize = sizeof(struct xt_tee_tginfo),
 223                 .checkentry = tee_tg_check,
 224                 .me         = THIS_MODULE,
 225         },
 226 #ifdef WITH_IPV6
 227         {
 228                 .name       = "TEE",
 229                 .revision   = 1,
 230                 .family     = NFPROTO_IPV6,
 231                 .target     = tee_tg6,
 232                 .targetsize = sizeof(struct xt_tee_tginfo),
 233                 .checkentry = tee_tg_check,
 234                 .me         = THIS_MODULE,
 235         },
 236 #endif
 237 };
 238
 239 static int __init tee_tg_init(void)
 240 {
 241         return xt_register_targets(tee_tg_reg, ARRAY_SIZE(tee_tg_reg));
 242 }
 243
 244 static void __exit tee_tg_exit(void)
 245 {
 246         xt_unregister_targets(tee_tg_reg, ARRAY_SIZE(tee_tg_reg));
 247 }
 248
 249 module_init(tee_tg_init);
 250 module_exit(tee_tg_exit);
 251 MODULE_AUTHOR("Sebastian Claßen <sebastian.classen@freenet.ag>");
 252 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 253 MODULE_DESCRIPTION("Xtables: Reroute packet copy");
 254 MODULE_LICENSE("GPL");
 255 MODULE_ALIAS("ipt_TEE");
 256 MODULE_ALIAS("ip6t_TEE");