net/netfilter/nft_hash.c

   1 /*
   2  * Copyright (c) 2016 Laura Garcia <nevola@gmail.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
  10 #include <linux/kernel.h>
  11 #include <linux/init.h>
  12 #include <linux/module.h>
  13 #include <linux/netlink.h>
  14 #include <linux/netfilter.h>
  15 #include <linux/netfilter/nf_tables.h>
  16 #include <net/netfilter/nf_tables.h>
  17 #include <net/netfilter/nf_tables_core.h>
  18 #include <linux/jhash.h>
  19
  20 struct nft_hash {
  21         enum nft_registers      sreg:8;
  22         enum nft_registers      dreg:8;
  23         u8                      len;
  24         u32                     modulus;
  25         u32                     seed;
  26         u32                     offset;
  27 };
  28
  29 static void nft_hash_eval(const struct nft_expr *expr,
  30                           struct nft_regs *regs,
  31                           const struct nft_pktinfo *pkt)
  32 {
  33         struct nft_hash *priv = nft_expr_priv(expr);
  34         const void *data = &regs->data[priv->sreg];
  35         u32 h;
  36
  37         h = reciprocal_scale(jhash(data, priv->len, priv->seed), priv->modulus);
  38         regs->data[priv->dreg] = h + priv->offset;
  39 }
  40
  41 static const struct nla_policy nft_hash_policy[NFTA_HASH_MAX + 1] = {
  42         [NFTA_HASH_SREG]        = { .type = NLA_U32 },
  43         [NFTA_HASH_DREG]        = { .type = NLA_U32 },
  44         [NFTA_HASH_LEN]         = { .type = NLA_U32 },
  45         [NFTA_HASH_MODULUS]     = { .type = NLA_U32 },
  46         [NFTA_HASH_SEED]        = { .type = NLA_U32 },
  47         [NFTA_HASH_OFFSET]      = { .type = NLA_U32 },
  48 };
  49
  50 static int nft_hash_init(const struct nft_ctx *ctx,
  51                          const struct nft_expr *expr,
  52                          const struct nlattr * const tb[])
  53 {
  54         struct nft_hash *priv = nft_expr_priv(expr);
  55         u32 len;
  56         int err;
  57
  58         if (!tb[NFTA_HASH_SREG] ||
  59             !tb[NFTA_HASH_DREG] ||
  60             !tb[NFTA_HASH_LEN]  ||
  61             !tb[NFTA_HASH_MODULUS])
  62                 return -EINVAL;
  63
  64         if (tb[NFTA_HASH_OFFSET])
  65                 priv->offset = ntohl(nla_get_be32(tb[NFTA_HASH_OFFSET]));
  66
  67         priv->sreg = nft_parse_register(tb[NFTA_HASH_SREG]);
  68         priv->dreg = nft_parse_register(tb[NFTA_HASH_DREG]);
  69
  70         err = nft_parse_u32_check(tb[NFTA_HASH_LEN], U8_MAX, &len);
  71         if (err < 0)
  72                 return err;
  73         if (len == 0)
  74                 return -ERANGE;
  75
  76         priv->len = len;
  77
  78         priv->modulus = ntohl(nla_get_be32(tb[NFTA_HASH_MODULUS]));
  79         if (priv->modulus <= 1)
  80                 return -ERANGE;
  81
  82         if (priv->offset + priv->modulus - 1 < priv->offset)
  83                 return -EOVERFLOW;
  84
  85         if (tb[NFTA_HASH_SEED])
  86                 priv->seed = ntohl(nla_get_be32(tb[NFTA_HASH_SEED]));
  87         else
  88                 get_random_bytes(&priv->seed, sizeof(priv->seed));
  89
  90         return nft_validate_register_load(priv->sreg, len) &&
  91                nft_validate_register_store(ctx, priv->dreg, NULL,
  92                                            NFT_DATA_VALUE, sizeof(u32));
  93 }
  94
  95 static int nft_hash_dump(struct sk_buff *skb,
  96                          const struct nft_expr *expr)
  97 {
  98         const struct nft_hash *priv = nft_expr_priv(expr);
  99
 100         if (nft_dump_register(skb, NFTA_HASH_SREG, priv->sreg))
 101                 goto nla_put_failure;
 102         if (nft_dump_register(skb, NFTA_HASH_DREG, priv->dreg))
 103                 goto nla_put_failure;
 104         if (nla_put_be32(skb, NFTA_HASH_LEN, htonl(priv->len)))
 105                 goto nla_put_failure;
 106         if (nla_put_be32(skb, NFTA_HASH_MODULUS, htonl(priv->modulus)))
 107                 goto nla_put_failure;
 108         if (nla_put_be32(skb, NFTA_HASH_SEED, htonl(priv->seed)))
 109                 goto nla_put_failure;
 110         if (priv->offset != 0)
 111                 if (nla_put_be32(skb, NFTA_HASH_OFFSET, htonl(priv->offset)))
 112                         goto nla_put_failure;
 113         return 0;
 114
 115 nla_put_failure:
 116         return -1;
 117 }
 118
 119 static struct nft_expr_type nft_hash_type;
 120 static const struct nft_expr_ops nft_hash_ops = {
 121         .type           = &nft_hash_type,
 122         .size           = NFT_EXPR_SIZE(sizeof(struct nft_hash)),
 123         .eval           = nft_hash_eval,
 124         .init           = nft_hash_init,
 125         .dump           = nft_hash_dump,
 126 };
 127
 128 static struct nft_expr_type nft_hash_type __read_mostly = {
 129         .name           = "hash",
 130         .ops            = &nft_hash_ops,
 131         .policy         = nft_hash_policy,
 132         .maxattr        = NFTA_HASH_MAX,
 133         .owner          = THIS_MODULE,
 134 };
 135
 136 static int __init nft_hash_module_init(void)
 137 {
 138         return nft_register_expr(&nft_hash_type);
 139 }
 140
 141 static void __exit nft_hash_module_exit(void)
 142 {
 143         nft_unregister_expr(&nft_hash_type);
 144 }
 145
 146 module_init(nft_hash_module_init);
 147 module_exit(nft_hash_module_exit);
 148
 149 MODULE_LICENSE("GPL");
 150 MODULE_AUTHOR("Laura Garcia <nevola@gmail.com>");
 151 MODULE_ALIAS_NFT_EXPR("hash");