net/ipv4/netfilter/ipt_rpfilter.c

   1 /*
   2  * Copyright (c) 2011 Florian Westphal <fw@strlen.de>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  *
   8  * based on fib_frontend.c; Author: Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
   9  */
  10 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  11 #include <linux/module.h>
  12 #include <linux/skbuff.h>
  13 #include <linux/netdevice.h>
  14 #include <linux/ip.h>
  15 #include <net/ip.h>
  16 #include <net/ip_fib.h>
  17 #include <net/route.h>
  18
  19 #include <linux/netfilter/xt_rpfilter.h>
  20 #include <linux/netfilter/x_tables.h>
  21
  22 MODULE_LICENSE("GPL");
  23 MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
  24 MODULE_DESCRIPTION("iptables: ipv4 reverse path filter match");
  25
  26 /* don't try to find route from mcast/bcast/zeronet */
  27 static __be32 rpfilter_get_saddr(__be32 addr)
  28 {
  29         if (ipv4_is_multicast(addr) || ipv4_is_lbcast(addr) ||
  30             ipv4_is_zeronet(addr))
  31                 return 0;
  32         return addr;
  33 }
  34
  35 static bool rpfilter_lookup_reverse(struct flowi4 *fl4,
  36                                 const struct net_device *dev, u8 flags)
  37 {
  38         struct fib_result res;
  39         bool dev_match;
  40         struct net *net = dev_net(dev);
  41         int ret __maybe_unused;
  42
  43         if (fib_lookup(net, fl4, &res))
  44                 return false;
  45
  46         if (res.type != RTN_UNICAST) {
  47                 if (res.type != RTN_LOCAL || !(flags & XT_RPFILTER_ACCEPT_LOCAL))
  48                         return false;
  49         }
  50         dev_match = false;
  51 #ifdef CONFIG_IP_ROUTE_MULTIPATH
  52         for (ret = 0; ret < res.fi->fib_nhs; ret++) {
  53                 struct fib_nh *nh = &res.fi->fib_nh[ret];
  54
  55                 if (nh->nh_dev == dev) {
  56                         dev_match = true;
  57                         break;
  58                 }
  59         }
  60 #else
  61         if (FIB_RES_DEV(res) == dev)
  62                 dev_match = true;
  63 #endif
  64         if (dev_match || flags & XT_RPFILTER_LOOSE)
  65                 return FIB_RES_NH(res).nh_scope <= RT_SCOPE_HOST;
  66         return dev_match;
  67 }
  68
  69 static bool rpfilter_is_local(const struct sk_buff *skb)
  70 {
  71         const struct rtable *rt = skb_rtable(skb);
  72         return rt && (rt->rt_flags & RTCF_LOCAL);
  73 }
  74
  75 static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
  76 {
  77         const struct xt_rpfilter_info *info;
  78         const struct iphdr *iph;
  79         struct flowi4 flow;
  80         bool invert;
  81
  82         info = par->matchinfo;
  83         invert = info->flags & XT_RPFILTER_INVERT;
  84
  85         if (rpfilter_is_local(skb))
  86                 return true ^ invert;
  87
  88         iph = ip_hdr(skb);
  89         if (ipv4_is_multicast(iph->daddr)) {
  90                 if (ipv4_is_zeronet(iph->saddr))
  91                         return ipv4_is_local_multicast(iph->daddr) ^ invert;
  92                 flow.flowi4_iif = 0;
  93         } else {
  94                 flow.flowi4_iif = LOOPBACK_IFINDEX;
  95         }
  96
  97         flow.daddr = iph->saddr;
  98         flow.saddr = rpfilter_get_saddr(iph->daddr);
  99         flow.flowi4_oif = 0;
 100         flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
 101         flow.flowi4_tos = RT_TOS(iph->tos);
 102         flow.flowi4_scope = RT_SCOPE_UNIVERSE;
 103
 104         return rpfilter_lookup_reverse(&flow, par->in, info->flags) ^ invert;
 105 }
 106
 107 static int rpfilter_check(const struct xt_mtchk_param *par)
 108 {
 109         const struct xt_rpfilter_info *info = par->matchinfo;
 110         unsigned int options = ~XT_RPFILTER_OPTION_MASK;
 111         if (info->flags & options) {
 112                 pr_info("unknown options encountered");
 113                 return -EINVAL;
 114         }
 115
 116         if (strcmp(par->table, "mangle") != 0 &&
 117             strcmp(par->table, "raw") != 0) {
 118                 pr_info("match only valid in the \'raw\' "
 119                         "or \'mangle\' tables, not \'%s\'.\n", par->table);
 120                 return -EINVAL;
 121         }
 122
 123         return 0;
 124 }
 125
 126 static struct xt_match rpfilter_mt_reg __read_mostly = {
 127         .name           = "rpfilter",
 128         .family         = NFPROTO_IPV4,
 129         .checkentry     = rpfilter_check,
 130         .match          = rpfilter_mt,
 131         .matchsize      = sizeof(struct xt_rpfilter_info),
 132         .hooks          = (1 << NF_INET_PRE_ROUTING),
 133         .me             = THIS_MODULE
 134 };
 135
 136 static int __init rpfilter_mt_init(void)
 137 {
 138         return xt_register_match(&rpfilter_mt_reg);
 139 }
 140
 141 static void __exit rpfilter_mt_exit(void)
 142 {
 143         xt_unregister_match(&rpfilter_mt_reg);
 144 }
 145
 146 module_init(rpfilter_mt_init);
 147 module_exit(rpfilter_mt_exit);