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 net *net, struct flowi4 *fl4,
  36                                 const struct net_device *dev, u8 flags)
  37 {
  38         struct fib_result res;
  39         int ret __maybe_unused;
  40
  41         if (fib_lookup(net, fl4, &res, FIB_LOOKUP_IGNORE_LINKSTATE))
  42                 return false;
  43
  44         if (res.type != RTN_UNICAST) {
  45                 if (res.type != RTN_LOCAL || !(flags & XT_RPFILTER_ACCEPT_LOCAL))
  46                         return false;
  47         }
  48         return fib_info_nh_uses_dev(res.fi, dev) || flags & XT_RPFILTER_LOOSE;
  49 }
  50
  51 static bool
  52 rpfilter_is_loopback(const struct sk_buff *skb, const struct net_device *in)
  53 {
  54         return skb->pkt_type == PACKET_LOOPBACK || in->flags & IFF_LOOPBACK;
  55 }
  56
  57 static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
  58 {
  59         const struct xt_rpfilter_info *info;
  60         const struct iphdr *iph;
  61         struct flowi4 flow;
  62         bool invert;
  63
  64         info = par->matchinfo;
  65         invert = info->flags & XT_RPFILTER_INVERT;
  66
  67         if (rpfilter_is_loopback(skb, xt_in(par)))
  68                 return true ^ invert;
  69
  70         iph = ip_hdr(skb);
  71         if (ipv4_is_zeronet(iph->saddr)) {
  72                 if (ipv4_is_lbcast(iph->daddr) ||
  73                     ipv4_is_local_multicast(iph->daddr))
  74                         return true ^ invert;
  75         }
  76
  77         memset(&flow, 0, sizeof(flow));
  78         flow.flowi4_iif = LOOPBACK_IFINDEX;
  79         flow.daddr = iph->saddr;
  80         flow.saddr = rpfilter_get_saddr(iph->daddr);
  81         flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
  82         flow.flowi4_tos = RT_TOS(iph->tos);
  83         flow.flowi4_scope = RT_SCOPE_UNIVERSE;
  84
  85         return rpfilter_lookup_reverse(xt_net(par), &flow, xt_in(par), info->flags) ^ invert;
  86 }
  87
  88 static int rpfilter_check(const struct xt_mtchk_param *par)
  89 {
  90         const struct xt_rpfilter_info *info = par->matchinfo;
  91         unsigned int options = ~XT_RPFILTER_OPTION_MASK;
  92         if (info->flags & options) {
  93                 pr_info_ratelimited("unknown options\n");
  94                 return -EINVAL;
  95         }
  96
  97         if (strcmp(par->table, "mangle") != 0 &&
  98             strcmp(par->table, "raw") != 0) {
  99                 pr_info_ratelimited("only valid in \'raw\' or \'mangle\' table, not \'%s\'\n",
 100                                     par->table);
 101                 return -EINVAL;
 102         }
 103
 104         return 0;
 105 }
 106
 107 static struct xt_match rpfilter_mt_reg __read_mostly = {
 108         .name           = "rpfilter",
 109         .family         = NFPROTO_IPV4,
 110         .checkentry     = rpfilter_check,
 111         .match          = rpfilter_mt,
 112         .matchsize      = sizeof(struct xt_rpfilter_info),
 113         .hooks          = (1 << NF_INET_PRE_ROUTING),
 114         .me             = THIS_MODULE
 115 };
 116
 117 static int __init rpfilter_mt_init(void)
 118 {
 119         return xt_register_match(&rpfilter_mt_reg);
 120 }
 121
 122 static void __exit rpfilter_mt_exit(void)
 123 {
 124         xt_unregister_match(&rpfilter_mt_reg);
 125 }
 126
 127 module_init(rpfilter_mt_init);
 128 module_exit(rpfilter_mt_exit);