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_mt(const struct sk_buff *skb, struct xt_action_param *par)
  70 {
  71         const struct xt_rpfilter_info *info;
  72         const struct iphdr *iph;
  73         struct flowi4 flow;
  74         bool invert;
  75
  76         info = par->matchinfo;
  77         invert = info->flags & XT_RPFILTER_INVERT;
  78
  79         if (par->in->flags & IFF_LOOPBACK)
  80                 return true ^ invert;
  81
  82         iph = ip_hdr(skb);
  83         if (ipv4_is_multicast(iph->daddr)) {
  84                 if (ipv4_is_zeronet(iph->saddr))
  85                         return ipv4_is_local_multicast(iph->daddr) ^ invert;
  86                 flow.flowi4_iif = 0;
  87         } else {
  88                 flow.flowi4_iif = dev_net(par->in)->loopback_dev->ifindex;
  89         }
  90
  91         flow.daddr = iph->saddr;
  92         flow.saddr = rpfilter_get_saddr(iph->daddr);
  93         flow.flowi4_oif = 0;
  94         flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
  95         flow.flowi4_tos = RT_TOS(iph->tos);
  96         flow.flowi4_scope = RT_SCOPE_UNIVERSE;
  97
  98         return rpfilter_lookup_reverse(&flow, par->in, info->flags) ^ invert;
  99 }
 100
 101 static int rpfilter_check(const struct xt_mtchk_param *par)
 102 {
 103         const struct xt_rpfilter_info *info = par->matchinfo;
 104         unsigned int options = ~XT_RPFILTER_OPTION_MASK;
 105         if (info->flags & options) {
 106                 pr_info("unknown options encountered");
 107                 return -EINVAL;
 108         }
 109
 110         if (strcmp(par->table, "mangle") != 0 &&
 111             strcmp(par->table, "raw") != 0) {
 112                 pr_info("match only valid in the \'raw\' "
 113                         "or \'mangle\' tables, not \'%s\'.\n", par->table);
 114                 return -EINVAL;
 115         }
 116
 117         return 0;
 118 }
 119
 120 static struct xt_match rpfilter_mt_reg __read_mostly = {
 121         .name           = "rpfilter",
 122         .family         = NFPROTO_IPV4,
 123         .checkentry     = rpfilter_check,
 124         .match          = rpfilter_mt,
 125         .matchsize      = sizeof(struct xt_rpfilter_info),
 126         .hooks          = (1 << NF_INET_PRE_ROUTING),
 127         .me             = THIS_MODULE
 128 };
 129
 130 static int __init rpfilter_mt_init(void)
 131 {
 132         return xt_register_match(&rpfilter_mt_reg);
 133 }
 134
 135 static void __exit rpfilter_mt_exit(void)
 136 {
 137         xt_unregister_match(&rpfilter_mt_reg);
 138 }
 139
 140 module_init(rpfilter_mt_init);
 141 module_exit(rpfilter_mt_exit);