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

---
Changes in V2:
- Define len as u8 instead of u32
- Improved module description
- Remove unnecessary includes
Changes in V3:
- Add null checks in init()
- Include registers load validation
Changes in V4:
- Use ERANGE in some cases according to the lib/nlattr.c policy
- Typo fixed
- Use nft_validate_register_load instead of nft_validate_register_store
Changes in V5:
- Use nft_validate_register_store for dreg in init()

 include/uapi/linux/netfilter/nf_tables.h |  20 +++++
 net/netfilter/Kconfig                    |   6 ++
 net/netfilter/Makefile                   |   1 +
 net/netfilter/nft_hash.c                 | 137 +++++++++++++++++++++++++++++++
 4 files changed, 164 insertions(+)
 create mode 100644 net/netfilter/nft_hash.c

index 533507b..13d25b9 100644
@@ -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)

index a2e4cf6..1074700 100644
@@ -569,6 +569,12 @@ 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

index 441a3c0..faa277e 100644
@@ -93,6 +93,7 @@ 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

2.8.1

Applied, thanks Laura.