netfilter: nf_tables: add hash expression

This patch adds a new hash expression, this provides jhash support but
this can be extended to support for other hash functions. The modulus
and seed already comes embedded into this new expression.

Use case example:

	... meta mark set hash ip saddr mod 10
Signed-off-by: Laura Garcia Liebana <nevola@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nf_tables.h

@@ -723,6 +723,26 @@ enum nft_meta_keys {
 	NFT_META_PRANDOM,
 };
 
+/**
+ * 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
  *

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

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

net/netfilter/nft_hash.c

+/*
+ * 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");