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Linux/net/ipv6/netfilter/ip6t_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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  9 #include <linux/module.h>
 10 #include <linux/skbuff.h>
 11 #include <linux/netdevice.h>
 12 #include <linux/route.h>
 13 #include <net/ip6_fib.h>
 14 #include <net/ip6_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("Xtables: IPv6 reverse path filter match");
 22 
 23 static bool rpfilter_addr_unicast(const struct in6_addr *addr)
 24 {
 25         int addr_type = ipv6_addr_type(addr);
 26         return addr_type & IPV6_ADDR_UNICAST;
 27 }
 28 
 29 static bool rpfilter_addr_linklocal(const struct in6_addr *addr)
 30 {
 31         int addr_type = ipv6_addr_type(addr);
 32         return addr_type & IPV6_ADDR_LINKLOCAL;
 33 }
 34 
 35 static bool rpfilter_lookup_reverse6(struct net *net, const struct sk_buff *skb,
 36                                      const struct net_device *dev, u8 flags)
 37 {
 38         struct rt6_info *rt;
 39         struct ipv6hdr *iph = ipv6_hdr(skb);
 40         bool ret = false;
 41         struct flowi6 fl6 = {
 42                 .flowi6_iif = LOOPBACK_IFINDEX,
 43                 .flowlabel = (* (__be32 *) iph) & IPV6_FLOWINFO_MASK,
 44                 .flowi6_proto = iph->nexthdr,
 45                 .daddr = iph->saddr,
 46         };
 47         int lookup_flags;
 48 
 49         if (rpfilter_addr_unicast(&iph->daddr)) {
 50                 memcpy(&fl6.saddr, &iph->daddr, sizeof(struct in6_addr));
 51                 lookup_flags = RT6_LOOKUP_F_HAS_SADDR;
 52         } else {
 53                 lookup_flags = 0;
 54         }
 55 
 56         fl6.flowi6_mark = flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
 57 
 58         if (rpfilter_addr_linklocal(&iph->saddr)) {
 59                 lookup_flags |= RT6_LOOKUP_F_IFACE;
 60                 fl6.flowi6_oif = dev->ifindex;
 61         } else if ((flags & XT_RPFILTER_LOOSE) == 0)
 62                 fl6.flowi6_oif = dev->ifindex;
 63 
 64         rt = (void *)ip6_route_lookup(net, &fl6, skb, lookup_flags);
 65         if (rt->dst.error)
 66                 goto out;
 67 
 68         if (rt->rt6i_flags & (RTF_REJECT|RTF_ANYCAST))
 69                 goto out;
 70 
 71         if (rt->rt6i_flags & RTF_LOCAL) {
 72                 ret = flags & XT_RPFILTER_ACCEPT_LOCAL;
 73                 goto out;
 74         }
 75 
 76         if (rt->rt6i_idev->dev == dev || (flags & XT_RPFILTER_LOOSE))
 77                 ret = true;
 78  out:
 79         ip6_rt_put(rt);
 80         return ret;
 81 }
 82 
 83 static bool
 84 rpfilter_is_loopback(const struct sk_buff *skb, const struct net_device *in)
 85 {
 86         return skb->pkt_type == PACKET_LOOPBACK || in->flags & IFF_LOOPBACK;
 87 }
 88 
 89 static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
 90 {
 91         const struct xt_rpfilter_info *info = par->matchinfo;
 92         int saddrtype;
 93         struct ipv6hdr *iph;
 94         bool invert = info->flags & XT_RPFILTER_INVERT;
 95 
 96         if (rpfilter_is_loopback(skb, xt_in(par)))
 97                 return true ^ invert;
 98 
 99         iph = ipv6_hdr(skb);
100         saddrtype = ipv6_addr_type(&iph->saddr);
101         if (unlikely(saddrtype == IPV6_ADDR_ANY))
102                 return true ^ invert; /* not routable: forward path will drop it */
103 
104         return rpfilter_lookup_reverse6(xt_net(par), skb, xt_in(par),
105                                         info->flags) ^ invert;
106 }
107 
108 static int rpfilter_check(const struct xt_mtchk_param *par)
109 {
110         const struct xt_rpfilter_info *info = par->matchinfo;
111         unsigned int options = ~XT_RPFILTER_OPTION_MASK;
112 
113         if (info->flags & options) {
114                 pr_info_ratelimited("unknown options\n");
115                 return -EINVAL;
116         }
117 
118         if (strcmp(par->table, "mangle") != 0 &&
119             strcmp(par->table, "raw") != 0) {
120                 pr_info_ratelimited("only valid in \'raw\' or \'mangle\' table, not \'%s\'\n",
121                                     par->table);
122                 return -EINVAL;
123         }
124 
125         return 0;
126 }
127 
128 static struct xt_match rpfilter_mt_reg __read_mostly = {
129         .name           = "rpfilter",
130         .family         = NFPROTO_IPV6,
131         .checkentry     = rpfilter_check,
132         .match          = rpfilter_mt,
133         .matchsize      = sizeof(struct xt_rpfilter_info),
134         .hooks          = (1 << NF_INET_PRE_ROUTING),
135         .me             = THIS_MODULE
136 };
137 
138 static int __init rpfilter_mt_init(void)
139 {
140         return xt_register_match(&rpfilter_mt_reg);
141 }
142 
143 static void __exit rpfilter_mt_exit(void)
144 {
145         xt_unregister_match(&rpfilter_mt_reg);
146 }
147 
148 module_init(rpfilter_mt_init);
149 module_exit(rpfilter_mt_exit);
150 

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