[07/29] netfilter: nf_tables: add hash expression

diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index 01751fa..6ce0a6d 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -724,6 +724,26 @@  enum nft_meta_keys {
 };
 
 /**
+ * enum nft_hash_attributes - nf_tables hash expression netlink attributes
+ *
+ * @NFTA_HASH_SREG: source register (NLA_U32)
+ * @NFTA_HASH_DREG: destination register (NLA_U32)
+ * @NFTA_HASH_LEN: source data length (NLA_U32)
+ * @NFTA_HASH_MODULUS: modulus value (NLA_U32)
+ * @NFTA_HASH_SEED: seed value (NLA_U32)
+ */
+enum nft_hash_attributes {
+	NFTA_HASH_UNSPEC,
+	NFTA_HASH_SREG,
+	NFTA_HASH_DREG,
+	NFTA_HASH_LEN,
+	NFTA_HASH_MODULUS,
+	NFTA_HASH_SEED,
+	__NFTA_HASH_MAX,
+};
+#define NFTA_HASH_MAX	(__NFTA_HASH_MAX - 1)
+
+/**
  * enum nft_meta_attributes - nf_tables meta expression netlink attributes
  *
  * @NFTA_META_DREG: destination register (NLA_U32)
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index e5740e1..9cfaa00 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -563,6 +563,12 @@  config NFT_COMPAT
 	  x_tables match/target extensions over the nf_tables
 	  framework.
 
+config NFT_HASH
+	tristate "Netfilter nf_tables hash module"
+	help
+	  This option adds the "hash" expression that you can use to perform
+	  a hash operation on registers.
+
 if NF_TABLES_NETDEV
 
 config NF_DUP_NETDEV
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 101fb85..1106ccd 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -92,6 +92,7 @@  obj-$(CONFIG_NFT_COUNTER)	+= nft_counter.o
 obj-$(CONFIG_NFT_LOG)		+= nft_log.o
 obj-$(CONFIG_NFT_MASQ)		+= nft_masq.o
 obj-$(CONFIG_NFT_REDIR)		+= nft_redir.o
+obj-$(CONFIG_NFT_HASH)		+= nft_hash.o
 
 # nf_tables netdev
 obj-$(CONFIG_NFT_DUP_NETDEV)	+= nft_dup_netdev.o
diff --git a/net/netfilter/nft_hash.c b/net/netfilter/nft_hash.c
new file mode 100644
index 0000000..b82ff29
--- /dev/null
+++ b/net/netfilter/nft_hash.c
@@ -0,0 +1,136 @@ 
+/*
+ * 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;
+};
+
+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];
+
+	regs->data[priv->dreg] =
+		reciprocal_scale(jhash(data, priv->len, priv->seed),
+				 priv->modulus);
+}
+
+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 },
+};
+
+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;
+
+	if (!tb[NFTA_HASH_SREG] ||
+	    !tb[NFTA_HASH_DREG] ||
+	    !tb[NFTA_HASH_LEN]  ||
+	    !tb[NFTA_HASH_SEED] ||
+	    !tb[NFTA_HASH_MODULUS])
+		return -EINVAL;
+
+	priv->sreg = nft_parse_register(tb[NFTA_HASH_SREG]);
+	priv->dreg = nft_parse_register(tb[NFTA_HASH_DREG]);
+
+	len = ntohl(nla_get_be32(tb[NFTA_HASH_LEN]));
+	if (len == 0 || len > U8_MAX)
+		return -ERANGE;
+
+	priv->len = len;
+
+	priv->modulus = ntohl(nla_get_be32(tb[NFTA_HASH_MODULUS]));
+	if (priv->modulus <= 1)
+		return -ERANGE;
+
+	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 (nft_dump_register(skb, NFTA_HASH_LEN, priv->len))
+		goto nla_put_failure;
+	if (nft_dump_register(skb, NFTA_HASH_MODULUS, priv->modulus))
+		goto nla_put_failure;
+	if (nft_dump_register(skb, NFTA_HASH_SEED, priv->seed))
+		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");