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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         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);
129 

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