LXR linux/net/ipv4/netfilter/ipt

   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
  19MODULE_LICENSE("GPL");
  20MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
  21MODULE_DESCRIPTION("iptables: ipv4 reverse path filter match");
  22
  23/* don't try to find route from mcast/bcast/zeronet */
  24static __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
  32static 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
  48static bool
  49rpfilter_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
  54static 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 = iph->tos & IPTOS_RT_MASK;
  80        flow.flowi4_scope = RT_SCOPE_UNIVERSE;
  81        flow.flowi4_oif = l3mdev_master_ifindex_rcu(xt_in(par));
  82
  83        return rpfilter_lookup_reverse(xt_net(par), &flow, xt_in(par), info->flags) ^ invert;
  84}
  85
  86static int rpfilter_check(const struct xt_mtchk_param *par)
  87{
  88        const struct xt_rpfilter_info *info = par->matchinfo;
  89        unsigned int options = ~XT_RPFILTER_OPTION_MASK;
  90        if (info->flags & options) {
  91                pr_info_ratelimited("unknown options\n");
  92                return -EINVAL;
  93        }
  94
  95        if (strcmp(par->table, "mangle") != 0 &&
  96            strcmp(par->table, "raw") != 0) {
  97                pr_info_ratelimited("only valid in \'raw\' or \'mangle\' table, not \'%s\'\n",
  98                                    par->table);
  99                return -EINVAL;
 100        }
 101
 102        return 0;
 103}
 104
 105static struct xt_match rpfilter_mt_reg __read_mostly = {
 106        .name           = "rpfilter",
 107        .family         = NFPROTO_IPV4,
 108        .checkentry     = rpfilter_check,
 109        .match          = rpfilter_mt,
 110        .matchsize      = sizeof(struct xt_rpfilter_info),
 111        .hooks          = (1 << NF_INET_PRE_ROUTING),
 112        .me             = THIS_MODULE
 113};
 114
 115static int __init rpfilter_mt_init(void)
 116{
 117        return xt_register_match(&rpfilter_mt_reg);
 118}
 119
 120static void __exit rpfilter_mt_exit(void)
 121{
 122        xt_unregister_match(&rpfilter_mt_reg);
 123}
 124
 125module_init(rpfilter_mt_init);
 126module_exit(rpfilter_mt_exit);
 127