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Linux/net/ipv4/netfilter/ipt_rpfilter.c

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  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         bool dev_match;
 40         int ret __maybe_unused;
 41 
 42         if (fib_lookup(net, fl4, &res, FIB_LOOKUP_IGNORE_LINKSTATE))
 43                 return false;
 44 
 45         if (res.type != RTN_UNICAST) {
 46                 if (res.type != RTN_LOCAL || !(flags & XT_RPFILTER_ACCEPT_LOCAL))
 47                         return false;
 48         }
 49         dev_match = false;
 50 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 51         for (ret = 0; ret < res.fi->fib_nhs; ret++) {
 52                 struct fib_nh *nh = &res.fi->fib_nh[ret];
 53 
 54                 if (nh->nh_dev == dev) {
 55                         dev_match = true;
 56                         break;
 57                 }
 58         }
 59 #else
 60         if (FIB_RES_DEV(res) == dev)
 61                 dev_match = true;
 62 #endif
 63         return dev_match || flags & XT_RPFILTER_LOOSE;
 64 }
 65 
 66 static bool rpfilter_is_local(const struct sk_buff *skb)
 67 {
 68         const struct rtable *rt = skb_rtable(skb);
 69         return rt && (rt->rt_flags & RTCF_LOCAL);
 70 }
 71 
 72 static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
 73 {
 74         const struct xt_rpfilter_info *info;
 75         const struct iphdr *iph;
 76         struct flowi4 flow;
 77         bool invert;
 78 
 79         info = par->matchinfo;
 80         invert = info->flags & XT_RPFILTER_INVERT;
 81 
 82         if (rpfilter_is_local(skb))
 83                 return true ^ invert;
 84 
 85         iph = ip_hdr(skb);
 86         if (ipv4_is_multicast(iph->daddr)) {
 87                 if (ipv4_is_zeronet(iph->saddr))
 88                         return ipv4_is_local_multicast(iph->daddr) ^ invert;
 89         }
 90         flow.flowi4_iif = LOOPBACK_IFINDEX;
 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(par->net, &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);
142 

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