net/netfilter/nft_rt.c

   1 /*
   2  * Copyright (c) 2016 Anders K. Pedersen <akp@cohaesio.com>
   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
   9 #include <linux/kernel.h>
  10 #include <linux/init.h>
  11 #include <linux/module.h>
  12 #include <linux/netlink.h>
  13 #include <linux/netfilter.h>
  14 #include <linux/netfilter/nf_tables.h>
  15 #include <net/dst.h>
  16 #include <net/ip6_route.h>
  17 #include <net/route.h>
  18 #include <net/netfilter/nf_tables.h>
  19 #include <net/netfilter/nf_tables_core.h>
  20
  21 struct nft_rt {
  22         enum nft_rt_keys        key:8;
  23         enum nft_registers      dreg:8;
  24 };
  25
  26 static u16 get_tcpmss(const struct nft_pktinfo *pkt, const struct dst_entry *skbdst)
  27 {
  28         u32 minlen = sizeof(struct ipv6hdr), mtu = dst_mtu(skbdst);
  29         const struct sk_buff *skb = pkt->skb;
  30         struct dst_entry *dst = NULL;
  31         struct flowi fl;
  32
  33         memset(&fl, 0, sizeof(fl));
  34
  35         switch (nft_pf(pkt)) {
  36         case NFPROTO_IPV4:
  37                 fl.u.ip4.daddr = ip_hdr(skb)->saddr;
  38                 minlen = sizeof(struct iphdr) + sizeof(struct tcphdr);
  39                 break;
  40         case NFPROTO_IPV6:
  41                 fl.u.ip6.daddr = ipv6_hdr(skb)->saddr;
  42                 minlen = sizeof(struct ipv6hdr) + sizeof(struct tcphdr);
  43                 break;
  44         }
  45
  46         nf_route(nft_net(pkt), &dst, &fl, false, nft_pf(pkt));
  47         if (dst) {
  48                 mtu = min(mtu, dst_mtu(dst));
  49                 dst_release(dst);
  50         }
  51
  52         if (mtu <= minlen || mtu > 0xffff)
  53                 return TCP_MSS_DEFAULT;
  54
  55         return mtu - minlen;
  56 }
  57
  58 static void nft_rt_get_eval(const struct nft_expr *expr,
  59                             struct nft_regs *regs,
  60                             const struct nft_pktinfo *pkt)
  61 {
  62         const struct nft_rt *priv = nft_expr_priv(expr);
  63         const struct sk_buff *skb = pkt->skb;
  64         u32 *dest = &regs->data[priv->dreg];
  65         const struct dst_entry *dst;
  66
  67         dst = skb_dst(skb);
  68         if (!dst)
  69                 goto err;
  70
  71         switch (priv->key) {
  72 #ifdef CONFIG_IP_ROUTE_CLASSID
  73         case NFT_RT_CLASSID:
  74                 *dest = dst->tclassid;
  75                 break;
  76 #endif
  77         case NFT_RT_NEXTHOP4:
  78                 if (nft_pf(pkt) != NFPROTO_IPV4)
  79                         goto err;
  80
  81                 *dest = (__force u32)rt_nexthop((const struct rtable *)dst,
  82                                                 ip_hdr(skb)->daddr);
  83                 break;
  84         case NFT_RT_NEXTHOP6:
  85                 if (nft_pf(pkt) != NFPROTO_IPV6)
  86                         goto err;
  87
  88                 memcpy(dest, rt6_nexthop((struct rt6_info *)dst,
  89                                          &ipv6_hdr(skb)->daddr),
  90                        sizeof(struct in6_addr));
  91                 break;
  92         case NFT_RT_TCPMSS:
  93                 nft_reg_store16(dest, get_tcpmss(pkt, dst));
  94                 break;
  95         default:
  96                 WARN_ON(1);
  97                 goto err;
  98         }
  99         return;
 100
 101 err:
 102         regs->verdict.code = NFT_BREAK;
 103 }
 104
 105 static const struct nla_policy nft_rt_policy[NFTA_RT_MAX + 1] = {
 106         [NFTA_RT_DREG]          = { .type = NLA_U32 },
 107         [NFTA_RT_KEY]           = { .type = NLA_U32 },
 108 };
 109
 110 static int nft_rt_get_init(const struct nft_ctx *ctx,
 111                            const struct nft_expr *expr,
 112                            const struct nlattr * const tb[])
 113 {
 114         struct nft_rt *priv = nft_expr_priv(expr);
 115         unsigned int len;
 116
 117         if (tb[NFTA_RT_KEY] == NULL ||
 118             tb[NFTA_RT_DREG] == NULL)
 119                 return -EINVAL;
 120
 121         priv->key = ntohl(nla_get_be32(tb[NFTA_RT_KEY]));
 122         switch (priv->key) {
 123 #ifdef CONFIG_IP_ROUTE_CLASSID
 124         case NFT_RT_CLASSID:
 125 #endif
 126         case NFT_RT_NEXTHOP4:
 127                 len = sizeof(u32);
 128                 break;
 129         case NFT_RT_NEXTHOP6:
 130                 len = sizeof(struct in6_addr);
 131                 break;
 132         case NFT_RT_TCPMSS:
 133                 len = sizeof(u16);
 134                 break;
 135         default:
 136                 return -EOPNOTSUPP;
 137         }
 138
 139         priv->dreg = nft_parse_register(tb[NFTA_RT_DREG]);
 140         return nft_validate_register_store(ctx, priv->dreg, NULL,
 141                                            NFT_DATA_VALUE, len);
 142 }
 143
 144 static int nft_rt_get_dump(struct sk_buff *skb,
 145                            const struct nft_expr *expr)
 146 {
 147         const struct nft_rt *priv = nft_expr_priv(expr);
 148
 149         if (nla_put_be32(skb, NFTA_RT_KEY, htonl(priv->key)))
 150                 goto nla_put_failure;
 151         if (nft_dump_register(skb, NFTA_RT_DREG, priv->dreg))
 152                 goto nla_put_failure;
 153         return 0;
 154
 155 nla_put_failure:
 156         return -1;
 157 }
 158
 159 static int nft_rt_validate(const struct nft_ctx *ctx, const struct nft_expr *expr,
 160                            const struct nft_data **data)
 161 {
 162         const struct nft_rt *priv = nft_expr_priv(expr);
 163         unsigned int hooks;
 164
 165         switch (priv->key) {
 166         case NFT_RT_NEXTHOP4:
 167         case NFT_RT_NEXTHOP6:
 168         case NFT_RT_CLASSID:
 169                 return 0;
 170         case NFT_RT_TCPMSS:
 171                 hooks = (1 << NF_INET_FORWARD) |
 172                         (1 << NF_INET_LOCAL_OUT) |
 173                         (1 << NF_INET_POST_ROUTING);
 174                 break;
 175         default:
 176                 return -EINVAL;
 177         }
 178
 179         return nft_chain_validate_hooks(ctx->chain, hooks);
 180 }
 181
 182 static struct nft_expr_type nft_rt_type;
 183 static const struct nft_expr_ops nft_rt_get_ops = {
 184         .type           = &nft_rt_type,
 185         .size           = NFT_EXPR_SIZE(sizeof(struct nft_rt)),
 186         .eval           = nft_rt_get_eval,
 187         .init           = nft_rt_get_init,
 188         .dump           = nft_rt_get_dump,
 189         .validate       = nft_rt_validate,
 190 };
 191
 192 static struct nft_expr_type nft_rt_type __read_mostly = {
 193         .name           = "rt",
 194         .ops            = &nft_rt_get_ops,
 195         .policy         = nft_rt_policy,
 196         .maxattr        = NFTA_RT_MAX,
 197         .owner          = THIS_MODULE,
 198 };
 199
 200 static int __init nft_rt_module_init(void)
 201 {
 202         return nft_register_expr(&nft_rt_type);
 203 }
 204
 205 static void __exit nft_rt_module_exit(void)
 206 {
 207         nft_unregister_expr(&nft_rt_type);
 208 }
 209
 210 module_init(nft_rt_module_init);
 211 module_exit(nft_rt_module_exit);
 212
 213 MODULE_LICENSE("GPL");
 214 MODULE_AUTHOR("Anders K. Pedersen <akp@cohaesio.com>");
 215 MODULE_ALIAS_NFT_EXPR("rt");