[PATCH] netfilter: nft_hash: Add hash offset value

[Laura Garcia Liebana]

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 sum 100

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

Signed-off-by: Laura Garcia Liebana <nev...@gmail.com>
---
 include/uapi/linux/netfilter/nf_tables.h |  2 ++
 net/netfilter/nft_hash.c                 | 13 +++++++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/netfilter/nf_tables.h 
b/include/uapi/linux/netfilter/nf_tables.h
index 4dbeeed..8026684 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -764,6 +764,7 @@ 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_SUM: Hash offset value (NLA_U32)
  */
 enum nft_hash_attributes {
        NFTA_HASH_UNSPEC,
@@ -772,6 +773,7 @@ enum nft_hash_attributes {
        NFTA_HASH_LEN,
        NFTA_HASH_MODULUS,
        NFTA_HASH_SEED,
+       NFTA_HASH_SUM,
        __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 b7e3b40..8ab04d9 100644
--- 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                     sum;
 };
 
 static void nft_hash_eval(const struct nft_expr *expr,
@@ -35,7 +36,7 @@ static void nft_hash_eval(const struct nft_expr *expr,
 
        h = reciprocal_scale(jhash(data, priv->len, priv->seed), priv->modulus);
 
-       regs->data[priv->dreg] = h;
+       regs->data[priv->dreg] = priv->sum + h;
 }
 
 const struct nla_policy nft_hash_policy[NFTA_HASH_MAX + 1] = {
@@ -44,6 +45,7 @@ const struct nla_policy nft_hash_policy[NFTA_HASH_MAX + 1] = {
        [NFTA_HASH_LEN]                 = { .type = NLA_U32 },
        [NFTA_HASH_MODULUS]             = { .type = NLA_U32 },
        [NFTA_HASH_SEED]                = { .type = NLA_U32 },
+       [NFTA_HASH_SUM]                 = { .type = NLA_U32 },
 };
 
 static int nft_hash_init(const struct nft_ctx *ctx,
@@ -60,6 +62,11 @@ static int nft_hash_init(const struct nft_ctx *ctx,
            !tb[NFTA_HASH_MODULUS])
                return -EINVAL;
 
+       if (tb[NFTA_HASH_SUM])
+               priv->sum = ntohl(nla_get_be32(tb[NFTA_HASH_SUM]));
+       else
+               priv->sum = 0;
+
        priv->sreg = nft_parse_register(tb[NFTA_HASH_SREG]);
        if (priv->sreg < 0)
                return -ERANGE;
@@ -99,7 +106,9 @@ static int nft_hash_dump(struct sk_buff *skb,
                goto nla_put_failure;
        if (nft_dump_register(skb, NFTA_HASH_SEED, priv->seed))
                goto nla_put_failure;
-
+       if (priv->sum != 0)
+               if (nft_dump_register(skb, NFTA_HASH_SUM, priv->sum))
+                       goto nla_put_failure;
        return 0;
 
 nla_put_failure:
-- 
2.8.1

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