netfilter: nft_hash: Add hash offset value

Add support to pass through an offset to the hash value. With this
feature, the sysadmin is able to generate a hash with a given
offset value.

Example:

	meta mark set jhash ip saddr mod 2 seed 0xabcd offset 100

This option generates marks according to the source address from 100 to
101.

Signed-off-by: Laura Garcia Liebana <nevola@gmail.com>

diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index 24161e2..8c653bb 100644 (file)
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -731,6 +731,7 @@ enum nft_meta_keys {
  * @NFTA_HASH_LEN: source data length (NLA_U32)
  * @NFTA_HASH_MODULUS: modulus value (NLA_U32)
  * @NFTA_HASH_SEED: seed value (NLA_U32)
+ * @NFTA_HASH_OFFSET: add this offset value to hash result (NLA_U32)
  */
 enum nft_hash_attributes {
        NFTA_HASH_UNSPEC,
@@ -739,6 +740,7 @@ enum nft_hash_attributes {
        NFTA_HASH_LEN,
        NFTA_HASH_MODULUS,
        NFTA_HASH_SEED,
+       NFTA_HASH_OFFSET,
        __NFTA_HASH_MAX,
 };
 #define NFTA_HASH_MAX  (__NFTA_HASH_MAX - 1)

diff --git a/net/netfilter/nft_hash.c b/net/netfilter/nft_hash.c
index 764251d..bd12f7a 100644 (file)
--- a/net/netfilter/nft_hash.c
+++ b/net/netfilter/nft_hash.c
@@ -23,6 +23,7 @@ struct nft_hash {
        u8                      len;
        u32                     modulus;
        u32                     seed;
+       u32                     offset;
 };
 
 static void nft_hash_eval(const struct nft_expr *expr,
@@ -31,10 +32,10 @@ static void nft_hash_eval(const struct nft_expr *expr,
 {
        struct nft_hash *priv = nft_expr_priv(expr);
        const void *data = &regs->data[priv->sreg];
+       u32 h;
 
-       regs->data[priv->dreg] =
-               reciprocal_scale(jhash(data, priv->len, priv->seed),
-                                priv->modulus);
+       h = reciprocal_scale(jhash(data, priv->len, priv->seed), priv->modulus);
+       regs->data[priv->dreg] = h + priv->offset;
 }
 
 static const struct nla_policy nft_hash_policy[NFTA_HASH_MAX + 1] = {
@@ -59,6 +60,9 @@ static int nft_hash_init(const struct nft_ctx *ctx,
            !tb[NFTA_HASH_MODULUS])
                return -EINVAL;
 
+       if (tb[NFTA_HASH_OFFSET])
+               priv->offset = ntohl(nla_get_be32(tb[NFTA_HASH_OFFSET]));
+
        priv->sreg = nft_parse_register(tb[NFTA_HASH_SREG]);
        priv->dreg = nft_parse_register(tb[NFTA_HASH_DREG]);
 
@@ -72,6 +76,9 @@ static int nft_hash_init(const struct nft_ctx *ctx,
        if (priv->modulus <= 1)
                return -ERANGE;
 
+       if (priv->offset + priv->modulus - 1 < U32_MAX)
+               return -EOVERFLOW;
+
        priv->seed = ntohl(nla_get_be32(tb[NFTA_HASH_SEED]));
 
        return nft_validate_register_load(priv->sreg, len) &&
@@ -94,7 +101,9 @@ static int nft_hash_dump(struct sk_buff *skb,
                goto nla_put_failure;
        if (nla_put_be32(skb, NFTA_HASH_SEED, htonl(priv->seed)))
                goto nla_put_failure;
-
+       if (priv->offset != 0)
+               if (nla_put_be32(skb, NFTA_HASH_OFFSET, htonl(priv->offset)))
+                       goto nla_put_failure;
        return 0;
 
 nla_put_failure: