net/ipv6/netfilter/ip6t_rpfilter.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (c) 2011 Florian Westphal <fw@strlen.de>
   4  */
   5 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   6 #include <linux/module.h>
   7 #include <linux/skbuff.h>
   8 #include <linux/netdevice.h>
   9 #include <linux/route.h>
  10 #include <net/ip6_fib.h>
  11 #include <net/ip6_route.h>
  12
  13 #include <linux/netfilter/xt_rpfilter.h>
  14 #include <linux/netfilter/x_tables.h>
  15
  16 MODULE_LICENSE("GPL");
  17 MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
  18 MODULE_DESCRIPTION("Xtables: IPv6 reverse path filter match");
  19
  20 static bool rpfilter_addr_unicast(const struct in6_addr *addr)
  21 {
  22         int addr_type = ipv6_addr_type(addr);
  23         return addr_type & IPV6_ADDR_UNICAST;
  24 }
  25
  26 static bool rpfilter_addr_linklocal(const struct in6_addr *addr)
  27 {
  28         int addr_type = ipv6_addr_type(addr);
  29         return addr_type & IPV6_ADDR_LINKLOCAL;
  30 }
  31
  32 static bool rpfilter_lookup_reverse6(struct net *net, const struct sk_buff *skb,
  33                                      const struct net_device *dev, u8 flags)
  34 {
  35         struct rt6_info *rt;
  36         struct ipv6hdr *iph = ipv6_hdr(skb);
  37         bool ret = false;
  38         struct flowi6 fl6 = {
  39                 .flowi6_iif = LOOPBACK_IFINDEX,
  40                 .flowlabel = (* (__be32 *) iph) & IPV6_FLOWINFO_MASK,
  41                 .flowi6_proto = iph->nexthdr,
  42                 .daddr = iph->saddr,
  43         };
  44         int lookup_flags;
  45
  46         if (rpfilter_addr_unicast(&iph->daddr)) {
  47                 memcpy(&fl6.saddr, &iph->daddr, sizeof(struct in6_addr));
  48                 lookup_flags = RT6_LOOKUP_F_HAS_SADDR;
  49         } else {
  50                 lookup_flags = 0;
  51         }
  52
  53         fl6.flowi6_mark = flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
  54
  55         if (rpfilter_addr_linklocal(&iph->saddr)) {
  56                 lookup_flags |= RT6_LOOKUP_F_IFACE;
  57                 fl6.flowi6_oif = dev->ifindex;
  58         } else if ((flags & XT_RPFILTER_LOOSE) == 0)
  59                 fl6.flowi6_oif = dev->ifindex;
  60
  61         rt = (void *)ip6_route_lookup(net, &fl6, skb, lookup_flags);
  62         if (rt->dst.error)
  63                 goto out;
  64
  65         if (rt->rt6i_flags & (RTF_REJECT|RTF_ANYCAST))
  66                 goto out;
  67
  68         if (rt->rt6i_flags & RTF_LOCAL) {
  69                 ret = flags & XT_RPFILTER_ACCEPT_LOCAL;
  70                 goto out;
  71         }
  72
  73         if (rt->rt6i_idev->dev == dev || (flags & XT_RPFILTER_LOOSE))
  74                 ret = true;
  75  out:
  76         ip6_rt_put(rt);
  77         return ret;
  78 }
  79
  80 static bool
  81 rpfilter_is_loopback(const struct sk_buff *skb, const struct net_device *in)
  82 {
  83         return skb->pkt_type == PACKET_LOOPBACK || in->flags & IFF_LOOPBACK;
  84 }
  85
  86 static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
  87 {
  88         const struct xt_rpfilter_info *info = par->matchinfo;
  89         int saddrtype;
  90         struct ipv6hdr *iph;
  91         bool invert = info->flags & XT_RPFILTER_INVERT;
  92
  93         if (rpfilter_is_loopback(skb, xt_in(par)))
  94                 return true ^ invert;
  95
  96         iph = ipv6_hdr(skb);
  97         saddrtype = ipv6_addr_type(&iph->saddr);
  98         if (unlikely(saddrtype == IPV6_ADDR_ANY))
  99                 return true ^ invert; /* not routable: forward path will drop it */
 100
 101         return rpfilter_lookup_reverse6(xt_net(par), skb, xt_in(par),
 102                                         info->flags) ^ invert;
 103 }
 104
 105 static int rpfilter_check(const struct xt_mtchk_param *par)
 106 {
 107         const struct xt_rpfilter_info *info = par->matchinfo;
 108         unsigned int options = ~XT_RPFILTER_OPTION_MASK;
 109
 110         if (info->flags & options) {
 111                 pr_info_ratelimited("unknown options\n");
 112                 return -EINVAL;
 113         }
 114
 115         if (strcmp(par->table, "mangle") != 0 &&
 116             strcmp(par->table, "raw") != 0) {
 117                 pr_info_ratelimited("only valid in \'raw\' or \'mangle\' table, not \'%s\'\n",
 118                                     par->table);
 119                 return -EINVAL;
 120         }
 121
 122         return 0;
 123 }
 124
 125 static struct xt_match rpfilter_mt_reg __read_mostly = {
 126         .name           = "rpfilter",
 127         .family         = NFPROTO_IPV6,
 128         .checkentry     = rpfilter_check,
 129         .match          = rpfilter_mt,
 130         .matchsize      = sizeof(struct xt_rpfilter_info),
 131         .hooks          = (1 << NF_INET_PRE_ROUTING),
 132         .me             = THIS_MODULE
 133 };
 134
 135 static int __init rpfilter_mt_init(void)
 136 {
 137         return xt_register_match(&rpfilter_mt_reg);
 138 }
 139
 140 static void __exit rpfilter_mt_exit(void)
 141 {
 142         xt_unregister_match(&rpfilter_mt_reg);
 143 }
 144
 145 module_init(rpfilter_mt_init);
 146 module_exit(rpfilter_mt_exit);