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         bool                    autogen_seed:1;
  25         u32                     modulus;
  26         u32                     seed;
  27         u32                     offset;
  28 };
  29
  30 static void nft_hash_eval(const struct nft_expr *expr,
  31                           struct nft_regs *regs,
  32                           const struct nft_pktinfo *pkt)
  33 {
  34         struct nft_hash *priv = nft_expr_priv(expr);
  35         const void *data = &regs->data[priv->sreg];
  36         u32 h;
  37
  38         h = reciprocal_scale(jhash(data, priv->len, priv->seed), priv->modulus);
  39         regs->data[priv->dreg] = h + priv->offset;
  40 }
  41
  42 static const struct nla_policy nft_hash_policy[NFTA_HASH_MAX + 1] = {
  43         [NFTA_HASH_SREG]        = { .type = NLA_U32 },
  44         [NFTA_HASH_DREG]        = { .type = NLA_U32 },
  45         [NFTA_HASH_LEN]         = { .type = NLA_U32 },
  46         [NFTA_HASH_MODULUS]     = { .type = NLA_U32 },
  47         [NFTA_HASH_SEED]        = { .type = NLA_U32 },
  48         [NFTA_HASH_OFFSET]      = { .type = NLA_U32 },
  49 };
  50
  51 static int nft_hash_init(const struct nft_ctx *ctx,
  52                          const struct nft_expr *expr,
  53                          const struct nlattr * const tb[])
  54 {
  55         struct nft_hash *priv = nft_expr_priv(expr);
  56         u32 len;
  57         int err;
  58
  59         if (!tb[NFTA_HASH_SREG] ||
  60             !tb[NFTA_HASH_DREG] ||
  61             !tb[NFTA_HASH_LEN]  ||
  62             !tb[NFTA_HASH_MODULUS])
  63                 return -EINVAL;
  64
  65         if (tb[NFTA_HASH_OFFSET])
  66                 priv->offset = ntohl(nla_get_be32(tb[NFTA_HASH_OFFSET]));
  67
  68         priv->sreg = nft_parse_register(tb[NFTA_HASH_SREG]);
  69         priv->dreg = nft_parse_register(tb[NFTA_HASH_DREG]);
  70
  71         err = nft_parse_u32_check(tb[NFTA_HASH_LEN], U8_MAX, &len);
  72         if (err < 0)
  73                 return err;
  74         if (len == 0)
  75                 return -ERANGE;
  76
  77         priv->len = len;
  78
  79         priv->modulus = ntohl(nla_get_be32(tb[NFTA_HASH_MODULUS]));
  80         if (priv->modulus <= 1)
  81                 return -ERANGE;
  82
  83         if (priv->offset + priv->modulus - 1 < priv->offset)
  84                 return -EOVERFLOW;
  85
  86         if (tb[NFTA_HASH_SEED]) {
  87                 priv->seed = ntohl(nla_get_be32(tb[NFTA_HASH_SEED]));
  88         } else {
  89                 priv->autogen_seed = true;
  90                 get_random_bytes(&priv->seed, sizeof(priv->seed));
  91         }
  92
  93         return nft_validate_register_load(priv->sreg, len) &&
  94                nft_validate_register_store(ctx, priv->dreg, NULL,
  95                                            NFT_DATA_VALUE, sizeof(u32));
  96 }
  97
  98 static int nft_hash_dump(struct sk_buff *skb,
  99                          const struct nft_expr *expr)
 100 {
 101         const struct nft_hash *priv = nft_expr_priv(expr);
 102
 103         if (nft_dump_register(skb, NFTA_HASH_SREG, priv->sreg))
 104                 goto nla_put_failure;
 105         if (nft_dump_register(skb, NFTA_HASH_DREG, priv->dreg))
 106                 goto nla_put_failure;
 107         if (nla_put_be32(skb, NFTA_HASH_LEN, htonl(priv->len)))
 108                 goto nla_put_failure;
 109         if (nla_put_be32(skb, NFTA_HASH_MODULUS, htonl(priv->modulus)))
 110                 goto nla_put_failure;
 111         if (!priv->autogen_seed &&
 112             nla_put_be32(skb, NFTA_HASH_SEED, htonl(priv->seed)))
 113                 goto nla_put_failure;
 114         if (priv->offset != 0)
 115                 if (nla_put_be32(skb, NFTA_HASH_OFFSET, htonl(priv->offset)))
 116                         goto nla_put_failure;
 117         return 0;
 118
 119 nla_put_failure:
 120         return -1;
 121 }
 122
 123 static struct nft_expr_type nft_hash_type;
 124 static const struct nft_expr_ops nft_hash_ops = {
 125         .type           = &nft_hash_type,
 126         .size           = NFT_EXPR_SIZE(sizeof(struct nft_hash)),
 127         .eval           = nft_hash_eval,
 128         .init           = nft_hash_init,
 129         .dump           = nft_hash_dump,
 130 };
 131
 132 static struct nft_expr_type nft_hash_type __read_mostly = {
 133         .name           = "hash",
 134         .ops            = &nft_hash_ops,
 135         .policy         = nft_hash_policy,
 136         .maxattr        = NFTA_HASH_MAX,
 137         .owner          = THIS_MODULE,
 138 };
 139
 140 static int __init nft_hash_module_init(void)
 141 {
 142         return nft_register_expr(&nft_hash_type);
 143 }
 144
 145 static void __exit nft_hash_module_exit(void)
 146 {
 147         nft_unregister_expr(&nft_hash_type);
 148 }
 149
 150 module_init(nft_hash_module_init);
 151 module_exit(nft_hash_module_exit);
 152
 153 MODULE_LICENSE("GPL");
 154 MODULE_AUTHOR("Laura Garcia <nevola@gmail.com>");
 155 MODULE_ALIAS_NFT_EXPR("hash");