net/ipv4/netfilter/ipt_rpfilter.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (c) 2011 Florian Westphal <fw@strlen.de>
   4  *
   5  * based on fib_frontend.c; Author: Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
   6  */
   7 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   8 #include <linux/module.h>
   9 #include <linux/skbuff.h>
  10 #include <linux/netdevice.h>
  11 #include <linux/ip.h>
  12 #include <net/ip.h>
  13 #include <net/ip_fib.h>
  14 #include <net/route.h>
  15
  16 #include <linux/netfilter/xt_rpfilter.h>
  17 #include <linux/netfilter/x_tables.h>
  18
  19 MODULE_LICENSE("GPL");
  20 MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
  21 MODULE_DESCRIPTION("iptables: ipv4 reverse path filter match");
  22
  23 /* don't try to find route from mcast/bcast/zeronet */
  24 static __be32 rpfilter_get_saddr(__be32 addr)
  25 {
  26         if (ipv4_is_multicast(addr) || ipv4_is_lbcast(addr) ||
  27             ipv4_is_zeronet(addr))
  28                 return 0;
  29         return addr;
  30 }
  31
  32 static bool rpfilter_lookup_reverse(struct net *net, struct flowi4 *fl4,
  33                                 const struct net_device *dev, u8 flags)
  34 {
  35         struct fib_result res;
  36         int ret __maybe_unused;
  37
  38         if (fib_lookup(net, fl4, &res, FIB_LOOKUP_IGNORE_LINKSTATE))
  39                 return false;
  40
  41         if (res.type != RTN_UNICAST) {
  42                 if (res.type != RTN_LOCAL || !(flags & XT_RPFILTER_ACCEPT_LOCAL))
  43                         return false;
  44         }
  45         return fib_info_nh_uses_dev(res.fi, dev) || flags & XT_RPFILTER_LOOSE;
  46 }
  47
  48 static bool
  49 rpfilter_is_loopback(const struct sk_buff *skb, const struct net_device *in)
  50 {
  51         return skb->pkt_type == PACKET_LOOPBACK || in->flags & IFF_LOOPBACK;
  52 }
  53
  54 static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
  55 {
  56         const struct xt_rpfilter_info *info;
  57         const struct iphdr *iph;
  58         struct flowi4 flow;
  59         bool invert;
  60
  61         info = par->matchinfo;
  62         invert = info->flags & XT_RPFILTER_INVERT;
  63
  64         if (rpfilter_is_loopback(skb, xt_in(par)))
  65                 return true ^ invert;
  66
  67         iph = ip_hdr(skb);
  68         if (ipv4_is_zeronet(iph->saddr)) {
  69                 if (ipv4_is_lbcast(iph->daddr) ||
  70                     ipv4_is_local_multicast(iph->daddr))
  71                         return true ^ invert;
  72         }
  73
  74         memset(&flow, 0, sizeof(flow));
  75         flow.flowi4_iif = LOOPBACK_IFINDEX;
  76         flow.daddr = iph->saddr;
  77         flow.saddr = rpfilter_get_saddr(iph->daddr);
  78         flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
  79         flow.flowi4_tos = RT_TOS(iph->tos);
  80         flow.flowi4_scope = RT_SCOPE_UNIVERSE;
  81
  82         return rpfilter_lookup_reverse(xt_net(par), &flow, xt_in(par), info->flags) ^ invert;
  83 }
  84
  85 static int rpfilter_check(const struct xt_mtchk_param *par)
  86 {
  87         const struct xt_rpfilter_info *info = par->matchinfo;
  88         unsigned int options = ~XT_RPFILTER_OPTION_MASK;
  89         if (info->flags & options) {
  90                 pr_info_ratelimited("unknown options\n");
  91                 return -EINVAL;
  92         }
  93
  94         if (strcmp(par->table, "mangle") != 0 &&
  95             strcmp(par->table, "raw") != 0) {
  96                 pr_info_ratelimited("only valid in \'raw\' or \'mangle\' table, not \'%s\'\n",
  97                                     par->table);
  98                 return -EINVAL;
  99         }
 100
 101         return 0;
 102 }
 103
 104 static struct xt_match rpfilter_mt_reg __read_mostly = {
 105         .name           = "rpfilter",
 106         .family         = NFPROTO_IPV4,
 107         .checkentry     = rpfilter_check,
 108         .match          = rpfilter_mt,
 109         .matchsize      = sizeof(struct xt_rpfilter_info),
 110         .hooks          = (1 << NF_INET_PRE_ROUTING),
 111         .me             = THIS_MODULE
 112 };
 113
 114 static int __init rpfilter_mt_init(void)
 115 {
 116         return xt_register_match(&rpfilter_mt_reg);
 117 }
 118
 119 static void __exit rpfilter_mt_exit(void)
 120 {
 121         xt_unregister_match(&rpfilter_mt_reg);
 122 }
 123
 124 module_init(rpfilter_mt_init);
 125 module_exit(rpfilter_mt_exit);