// SPDX-License-Identifier: GPL-2.0-only

  /*
   * Copyright (c) 2016 Laura Garcia <nevola@gmail.com>

   */
  
  #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 <linux/static_key.h>
  #include <net/netfilter/nf_tables.h>
  #include <net/netfilter/nf_tables_core.h>
  
  static DEFINE_PER_CPU(struct rnd_state, nft_numgen_prandom_state);
  
  struct nft_ng_inc {
  	enum nft_registers      dreg:8;

  	u32			modulus;

  	atomic_t		counter;

  	u32			offset;

  };

  static u32 nft_ng_inc_gen(struct nft_ng_inc *priv)

  {

  	u32 nval, oval;
  
  	do {
  		oval = atomic_read(&priv->counter);

  		nval = (oval + 1 < priv->modulus) ? oval + 1 : 0;

  	} while (atomic_cmpxchg(&priv->counter, oval, nval) != oval);

  	return nval + priv->offset;
  }
  
  static void nft_ng_inc_eval(const struct nft_expr *expr,
  			    struct nft_regs *regs,
  			    const struct nft_pktinfo *pkt)
  {
  	struct nft_ng_inc *priv = nft_expr_priv(expr);
  
  	regs->data[priv->dreg] = nft_ng_inc_gen(priv);
  }

  static const struct nla_policy nft_ng_policy[NFTA_NG_MAX + 1] = {
  	[NFTA_NG_DREG]		= { .type = NLA_U32 },

  	[NFTA_NG_MODULUS]	= { .type = NLA_U32 },

  	[NFTA_NG_TYPE]		= { .type = NLA_U32 },

  	[NFTA_NG_OFFSET]	= { .type = NLA_U32 },

  };
  
  static int nft_ng_inc_init(const struct nft_ctx *ctx,
  			   const struct nft_expr *expr,
  			   const struct nlattr * const tb[])
  {
  	struct nft_ng_inc *priv = nft_expr_priv(expr);

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

  	priv->modulus = ntohl(nla_get_be32(tb[NFTA_NG_MODULUS]));
  	if (priv->modulus == 0)

  		return -ERANGE;

  	if (priv->offset + priv->modulus - 1 < priv->offset)
  		return -EOVERFLOW;

  	priv->dreg = nft_parse_register(tb[NFTA_NG_DREG]);

  	atomic_set(&priv->counter, priv->modulus - 1);

  
  	return nft_validate_register_store(ctx, priv->dreg, NULL,
  					   NFT_DATA_VALUE, sizeof(u32));
  }
  
  static int nft_ng_dump(struct sk_buff *skb, enum nft_registers dreg,

  		       u32 modulus, enum nft_ng_types type, u32 offset)

  {
  	if (nft_dump_register(skb, NFTA_NG_DREG, dreg))
  		goto nla_put_failure;

  	if (nla_put_be32(skb, NFTA_NG_MODULUS, htonl(modulus)))

  		goto nla_put_failure;

  	if (nla_put_be32(skb, NFTA_NG_TYPE, htonl(type)))

  		goto nla_put_failure;

  	if (nla_put_be32(skb, NFTA_NG_OFFSET, htonl(offset)))
  		goto nla_put_failure;

  
  	return 0;
  
  nla_put_failure:
  	return -1;
  }
  
  static int nft_ng_inc_dump(struct sk_buff *skb, const struct nft_expr *expr)
  {
  	const struct nft_ng_inc *priv = nft_expr_priv(expr);

  	return nft_ng_dump(skb, priv->dreg, priv->modulus, NFT_NG_INCREMENTAL,
  			   priv->offset);

  }
  
  struct nft_ng_random {
  	enum nft_registers      dreg:8;

  	u32			modulus;

  	u32			offset;

  };

  static u32 nft_ng_random_gen(struct nft_ng_random *priv)
  {
  	struct rnd_state *state = this_cpu_ptr(&nft_numgen_prandom_state);
  
  	return reciprocal_scale(prandom_u32_state(state), priv->modulus) +
  	       priv->offset;
  }

  static void nft_ng_random_eval(const struct nft_expr *expr,
  			       struct nft_regs *regs,
  			       const struct nft_pktinfo *pkt)
  {
  	struct nft_ng_random *priv = nft_expr_priv(expr);

  	regs->data[priv->dreg] = nft_ng_random_gen(priv);
  }

  static int nft_ng_random_init(const struct nft_ctx *ctx,
  			      const struct nft_expr *expr,
  			      const struct nlattr * const tb[])
  {
  	struct nft_ng_random *priv = nft_expr_priv(expr);

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

  	priv->modulus = ntohl(nla_get_be32(tb[NFTA_NG_MODULUS]));
  	if (priv->modulus == 0)

  		return -ERANGE;

  	if (priv->offset + priv->modulus - 1 < priv->offset)
  		return -EOVERFLOW;

  	prandom_init_once(&nft_numgen_prandom_state);
  
  	priv->dreg = nft_parse_register(tb[NFTA_NG_DREG]);
  
  	return nft_validate_register_store(ctx, priv->dreg, NULL,
  					   NFT_DATA_VALUE, sizeof(u32));
  }
  
  static int nft_ng_random_dump(struct sk_buff *skb, const struct nft_expr *expr)
  {
  	const struct nft_ng_random *priv = nft_expr_priv(expr);

  	return nft_ng_dump(skb, priv->dreg, priv->modulus, NFT_NG_RANDOM,
  			   priv->offset);

  }
  
  static struct nft_expr_type nft_ng_type;
  static const struct nft_expr_ops nft_ng_inc_ops = {
  	.type		= &nft_ng_type,
  	.size		= NFT_EXPR_SIZE(sizeof(struct nft_ng_inc)),
  	.eval		= nft_ng_inc_eval,
  	.init		= nft_ng_inc_init,
  	.dump		= nft_ng_inc_dump,
  };
  
  static const struct nft_expr_ops nft_ng_random_ops = {
  	.type		= &nft_ng_type,
  	.size		= NFT_EXPR_SIZE(sizeof(struct nft_ng_random)),
  	.eval		= nft_ng_random_eval,
  	.init		= nft_ng_random_init,
  	.dump		= nft_ng_random_dump,
  };
  
  static const struct nft_expr_ops *
  nft_ng_select_ops(const struct nft_ctx *ctx, const struct nlattr * const tb[])
  {
  	u32 type;

  	if (!tb[NFTA_NG_DREG]	 ||
  	    !tb[NFTA_NG_MODULUS] ||

  	    !tb[NFTA_NG_TYPE])
  		return ERR_PTR(-EINVAL);
  
  	type = ntohl(nla_get_be32(tb[NFTA_NG_TYPE]));
  
  	switch (type) {
  	case NFT_NG_INCREMENTAL:
  		return &nft_ng_inc_ops;
  	case NFT_NG_RANDOM:
  		return &nft_ng_random_ops;
  	}
  
  	return ERR_PTR(-EINVAL);
  }
  
  static struct nft_expr_type nft_ng_type __read_mostly = {
  	.name		= "numgen",

  	.select_ops	= nft_ng_select_ops,

  	.policy		= nft_ng_policy,
  	.maxattr	= NFTA_NG_MAX,
  	.owner		= THIS_MODULE,
  };
  
  static int __init nft_ng_module_init(void)
  {
  	return nft_register_expr(&nft_ng_type);
  }
  
  static void __exit nft_ng_module_exit(void)
  {
  	nft_unregister_expr(&nft_ng_type);
  }
  
  module_init(nft_ng_module_init);
  module_exit(nft_ng_module_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Laura Garcia <nevola@gmail.com>");
  MODULE_ALIAS_NFT_EXPR("numgen");