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