[PATCH] netfilter: nft_hash: generate Jenkins Hash per source register

[Laura Garcia Liebana <nevola@gmail.com>]

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 comes already come 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>
---
 include/uapi/linux/netfilter/nf_tables.h |  20 +++++
 net/netfilter/Kconfig                    |   6 ++
 net/netfilter/Makefile                   |   1 +
 net/netfilter/nft_hash.c                 | 134 +++++++++++++++++++++++++++++++
 4 files changed, 161 insertions(+)
 create mode 100644 net/netfilter/nft_hash.c

diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index 0e7928e..5e74c05 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -1097,4 +1097,24 @@ enum nft_nth_attributes {
 };
 #define NFTA_NTH_MAX	(__NFTA_NTH_MAX - 1)
 
+/**
+ * enum nft_hash_attributes - nf_tables hash expression netlink attributes
+ * @NFTA_HASH_UNSPEC: unspecified attribute
+ * @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)
+
 #endif /* _LINUX_NF_TABLES_H */
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index a2e4cf6..f821902 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -480,6 +480,12 @@ config NFT_NTH
 	  This option adds the "nth" expression that you can use to match a
 	  packet every a specific given value.
 
+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.
+
 config NFT_CT
 	depends on NF_CONNTRACK
 	tristate "Netfilter nf_tables conntrack module"
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 441a3c0..fd11c6d 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -81,6 +81,7 @@ obj-$(CONFIG_NFT_COMPAT)	+= nft_compat.o
 obj-$(CONFIG_NFT_EXTHDR)	+= nft_exthdr.o
 obj-$(CONFIG_NFT_META)		+= nft_meta.o
 obj-$(CONFIG_NFT_NTH)		+= nft_nth.o
+obj-$(CONFIG_NFT_HASH)		+= nft_hash.o
 obj-$(CONFIG_NFT_CT)		+= nft_ct.o
 obj-$(CONFIG_NFT_LIMIT)		+= nft_limit.o
 obj-$(CONFIG_NFT_NAT)		+= nft_nat.o
diff --git a/net/netfilter/nft_hash.c b/net/netfilter/nft_hash.c
new file mode 100644
index 0000000..bb124aa
--- /dev/null
+++ b/net/netfilter/nft_hash.c
@@ -0,0 +1,134 @@
+/*
+ * 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 <linux/in.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/static_key.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;
+	u32			len:8;
+	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];
+	u32 h;
+
+	h = reciprocal_scale(jhash(data, priv->len, priv->seed), priv->modulus);
+
+	regs->data[priv->dreg] = h;
+}
+
+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);
+
+	if (!tb[NFTA_HASH_SREG] ||
+	    !tb[NFTA_HASH_DREG] ||
+	    !tb[NFTA_HASH_LEN])
+		return -EINVAL;
+
+	priv->sreg = nft_parse_register(tb[NFTA_HASH_SREG]);
+	priv->dreg = nft_parse_register(tb[NFTA_HASH_DREG]);
+
+	priv->len = ntohl(nla_get_be32(tb[NFTA_HASH_LEN]));
+	if (priv->len == 0)
+		return -EINVAL;
+
+	priv->modulus = ntohl(nla_get_be32(tb[NFTA_HASH_MODULUS]));
+	if (priv->modulus <= 1)
+		return -EINVAL;
+
+	priv->seed = ntohl(nla_get_be32(tb[NFTA_HASH_SEED]));
+
+	return 0;
+}
+
+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");
-- 
2.8.1