/*
   * Copyright (c) 2016 Laura Garcia <nevola@gmail.com>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation.
   *
   */
  
  #include <linux/kernel.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/netlink.h>
  #include <linux/netfilter.h>
  #include <linux/netfilter/nf_tables.h>
  #include <net/netfilter/nf_tables.h>
  #include <net/netfilter/nf_tables_core.h>
  #include <linux/jhash.h>
  
  struct nft_hash {
  	enum nft_registers      sreg:8;
  	enum nft_registers      dreg:8;
  	u8			len;
  	u32			modulus;
  	u32			seed;

  	u32			offset;

  };
  
  static void nft_hash_eval(const struct nft_expr *expr,
  			  struct nft_regs *regs,
  			  const struct nft_pktinfo *pkt)
  {
  	struct nft_hash *priv = nft_expr_priv(expr);
  	const void *data = &regs->data[priv->sreg];

  	u32 h;

  	h = reciprocal_scale(jhash(data, priv->len, priv->seed), priv->modulus);
  	regs->data[priv->dreg] = h + priv->offset;

  }

  static const struct nla_policy nft_hash_policy[NFTA_HASH_MAX + 1] = {

  	[NFTA_HASH_SREG]	= { .type = NLA_U32 },
  	[NFTA_HASH_DREG]	= { .type = NLA_U32 },
  	[NFTA_HASH_LEN]		= { .type = NLA_U32 },
  	[NFTA_HASH_MODULUS]	= { .type = NLA_U32 },
  	[NFTA_HASH_SEED]	= { .type = NLA_U32 },

  	[NFTA_HASH_OFFSET]	= { .type = NLA_U32 },

  };
  
  static int nft_hash_init(const struct nft_ctx *ctx,
  			 const struct nft_expr *expr,
  			 const struct nlattr * const tb[])
  {
  	struct nft_hash *priv = nft_expr_priv(expr);
  	u32 len;

  	int err;

  
  	if (!tb[NFTA_HASH_SREG] ||
  	    !tb[NFTA_HASH_DREG] ||
  	    !tb[NFTA_HASH_LEN]  ||
  	    !tb[NFTA_HASH_SEED] ||
  	    !tb[NFTA_HASH_MODULUS])
  		return -EINVAL;

  	if (tb[NFTA_HASH_OFFSET])
  		priv->offset = ntohl(nla_get_be32(tb[NFTA_HASH_OFFSET]));

  	priv->sreg = nft_parse_register(tb[NFTA_HASH_SREG]);
  	priv->dreg = nft_parse_register(tb[NFTA_HASH_DREG]);

  	err = nft_parse_u32_check(tb[NFTA_HASH_LEN], U8_MAX, &len);
  	if (err < 0)
  		return err;
  	if (len == 0)

  		return -ERANGE;
  
  	priv->len = len;
  
  	priv->modulus = ntohl(nla_get_be32(tb[NFTA_HASH_MODULUS]));
  	if (priv->modulus <= 1)
  		return -ERANGE;

  	if (priv->offset + priv->modulus - 1 < priv->offset)

  		return -EOVERFLOW;

  	priv->seed = ntohl(nla_get_be32(tb[NFTA_HASH_SEED]));
  
  	return nft_validate_register_load(priv->sreg, len) &&
  	       nft_validate_register_store(ctx, priv->dreg, NULL,
  					   NFT_DATA_VALUE, sizeof(u32));
  }
  
  static int nft_hash_dump(struct sk_buff *skb,
  			 const struct nft_expr *expr)
  {
  	const struct nft_hash *priv = nft_expr_priv(expr);
  
  	if (nft_dump_register(skb, NFTA_HASH_SREG, priv->sreg))
  		goto nla_put_failure;
  	if (nft_dump_register(skb, NFTA_HASH_DREG, priv->dreg))
  		goto nla_put_failure;

  	if (nla_put_be32(skb, NFTA_HASH_LEN, htonl(priv->len)))

  		goto nla_put_failure;

  	if (nla_put_be32(skb, NFTA_HASH_MODULUS, htonl(priv->modulus)))

  		goto nla_put_failure;

  	if (nla_put_be32(skb, NFTA_HASH_SEED, htonl(priv->seed)))

  		goto nla_put_failure;

  	if (priv->offset != 0)
  		if (nla_put_be32(skb, NFTA_HASH_OFFSET, htonl(priv->offset)))
  			goto nla_put_failure;

  	return 0;
  
  nla_put_failure:
  	return -1;
  }
  
  static struct nft_expr_type nft_hash_type;
  static const struct nft_expr_ops nft_hash_ops = {
  	.type		= &nft_hash_type,
  	.size		= NFT_EXPR_SIZE(sizeof(struct nft_hash)),
  	.eval		= nft_hash_eval,
  	.init		= nft_hash_init,
  	.dump		= nft_hash_dump,
  };
  
  static struct nft_expr_type nft_hash_type __read_mostly = {
  	.name		= "hash",
  	.ops		= &nft_hash_ops,
  	.policy		= nft_hash_policy,
  	.maxattr	= NFTA_HASH_MAX,
  	.owner		= THIS_MODULE,
  };
  
  static int __init nft_hash_module_init(void)
  {
  	return nft_register_expr(&nft_hash_type);
  }
  
  static void __exit nft_hash_module_exit(void)
  {
  	nft_unregister_expr(&nft_hash_type);
  }
  
  module_init(nft_hash_module_init);
  module_exit(nft_hash_module_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Laura Garcia <nevola@gmail.com>");
  MODULE_ALIAS_NFT_EXPR("hash");