On Mon, Apr 23, 2018 at 12:48:07PM +0200, Laura Garcia Liebana wrote:
> The modulus in the hash function was limited to > 1 as initially
> there was no sense to create a hashing of just one element.
>
> Nevertheless, there are certain cases specially for load balancing
> where this case needs to be addressed.
>
> This patch fixes the following error.
>
> Error: Could not process rule: Numerical result out of range
> add rule ip nftlb lb01 dnat to jhash ip saddr mod 1 map { 0: 192.168.0.10 }
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> The solution comes to force the hash to 0 when the modulus is 1.
Applied, but see comment below.
> Signed-off-by: Laura Garcia Liebana <[email protected]>
> ---
> net/netfilter/nft_hash.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/net/netfilter/nft_hash.c b/net/netfilter/nft_hash.c
> index 24f2f7567ddb..1c4f791552d0 100644
> --- a/net/netfilter/nft_hash.c
> +++ b/net/netfilter/nft_hash.c
> @@ -53,7 +53,11 @@ static void nft_symhash_eval(const struct nft_expr *expr,
> struct sk_buff *skb = pkt->skb;
> u32 h;
>
> - h = reciprocal_scale(__skb_get_hash_symmetric(skb), priv->modulus);
> + if (priv->modulus)
> + h = reciprocal_scale(__skb_get_hash_symmetric(skb),
> + priv->modulus);
> + else
> + h = 0;
I have left this chunk behind, this looks like an early optimization
to me. For the case where we only have one single element in the map,
reciprocal_scale will return zero for this, so no need for the extra
branch.
> regs->data[priv->dreg] = h + priv->offset;
> }
> @@ -97,7 +101,7 @@ static int nft_jhash_init(const struct nft_ctx *ctx,
> priv->len = len;
>
> priv->modulus = ntohl(nla_get_be32(tb[NFTA_HASH_MODULUS]));
> - if (priv->modulus <= 1)
> + if (priv->modulus < 1)
> return -ERANGE;
>
> if (priv->offset + priv->modulus - 1 < priv->offset)
> --
> 2.11.0
>
> --
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