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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_lookup_reverse6(const struct sk_buff *skb,
 30                                      const struct net_device *dev, u8 flags)
 31 {
 32         struct rt6_info *rt;
 33         struct ipv6hdr *iph = ipv6_hdr(skb);
 34         bool ret = false;
 35         struct flowi6 fl6 = {
 36                 .flowlabel = (* (__be32 *) iph) & IPV6_FLOWINFO_MASK,
 37                 .flowi6_proto = iph->nexthdr,
 38                 .daddr = iph->saddr,
 39         };
 40         int lookup_flags;
 41 
 42         if (rpfilter_addr_unicast(&iph->daddr)) {
 43                 memcpy(&fl6.saddr, &iph->daddr, sizeof(struct in6_addr));
 44                 lookup_flags = RT6_LOOKUP_F_HAS_SADDR;
 45         } else {
 46                 lookup_flags = 0;
 47         }
 48 
 49         fl6.flowi6_mark = flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
 50         if ((flags & XT_RPFILTER_LOOSE) == 0) {
 51                 fl6.flowi6_oif = dev->ifindex;
 52                 lookup_flags |= RT6_LOOKUP_F_IFACE;
 53         }
 54 
 55         rt = (void *) ip6_route_lookup(dev_net(dev), &fl6, lookup_flags);
 56         if (rt->dst.error)
 57                 goto out;
 58 
 59         if (rt->rt6i_flags & (RTF_REJECT|RTF_ANYCAST))
 60                 goto out;
 61 
 62         if (rt->rt6i_flags & RTF_LOCAL) {
 63                 ret = flags & XT_RPFILTER_ACCEPT_LOCAL;
 64                 goto out;
 65         }
 66 
 67         if (rt->rt6i_idev->dev == dev || (flags & XT_RPFILTER_LOOSE))
 68                 ret = true;
 69  out:
 70         ip6_rt_put(rt);
 71         return ret;
 72 }
 73 
 74 static bool rpfilter_is_local(const struct sk_buff *skb)
 75 {
 76         const struct rt6_info *rt = (const void *) skb_dst(skb);
 77         return rt && (rt->rt6i_flags & RTF_LOCAL);
 78 }
 79 
 80 static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
 81 {
 82         const struct xt_rpfilter_info *info = par->matchinfo;
 83         int saddrtype;
 84         struct ipv6hdr *iph;
 85         bool invert = info->flags & XT_RPFILTER_INVERT;
 86 
 87         if (rpfilter_is_local(skb))
 88                 return true ^ invert;
 89 
 90         iph = ipv6_hdr(skb);
 91         saddrtype = ipv6_addr_type(&iph->saddr);
 92         if (unlikely(saddrtype == IPV6_ADDR_ANY))
 93                 return true ^ invert; /* not routable: forward path will drop it */
 94 
 95         return rpfilter_lookup_reverse6(skb, par->in, info->flags) ^ invert;
 96 }
 97 
 98 static int rpfilter_check(const struct xt_mtchk_param *par)
 99 {
100         const struct xt_rpfilter_info *info = par->matchinfo;
101         unsigned int options = ~XT_RPFILTER_OPTION_MASK;
102 
103         if (info->flags & options) {
104                 pr_info("unknown options encountered");
105                 return -EINVAL;
106         }
107 
108         if (strcmp(par->table, "mangle") != 0 &&
109             strcmp(par->table, "raw") != 0) {
110                 pr_info("match only valid in the \'raw\' "
111                         "or \'mangle\' tables, not \'%s\'.\n", par->table);
112                 return -EINVAL;
113         }
114 
115         return 0;
116 }
117 
118 static struct xt_match rpfilter_mt_reg __read_mostly = {
119         .name           = "rpfilter",
120         .family         = NFPROTO_IPV6,
121         .checkentry     = rpfilter_check,
122         .match          = rpfilter_mt,
123         .matchsize      = sizeof(struct xt_rpfilter_info),
124         .hooks          = (1 << NF_INET_PRE_ROUTING),
125         .me             = THIS_MODULE
126 };
127 
128 static int __init rpfilter_mt_init(void)
129 {
130         return xt_register_match(&rpfilter_mt_reg);
131 }
132 
133 static void __exit rpfilter_mt_exit(void)
134 {
135         xt_unregister_match(&rpfilter_mt_reg);
136 }
137 
138 module_init(rpfilter_mt_init);
139 module_exit(rpfilter_mt_exit);
140 

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