Re: [PATCH] netfilter: nf_tables: check if payload offset is a power of 2

[Patrick McHardy <kaber@trash.net>]

On Sun, Feb 16, 2014 at 12:54:40PM +0100, Nikolay Aleksandrov wrote:
> Add a check if payload's offset is a power of 2 when selecting ops.
> The fast ops were meant for well aligned offsets, also this fixes a
> small bug when using unaligned offset and length of 3 which causes
> only 1 byte to be loaded because the fast ops are chosen.
> 
> Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
> ---
> I broke the line since it was >80 chars.
> This patch applies to Dave's -net tree.
> 
>  net/netfilter/nft_payload.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c
> index a2aeb31..15a3dcb 100644
> --- a/net/netfilter/nft_payload.c
> +++ b/net/netfilter/nft_payload.c
> @@ -135,7 +135,9 @@ nft_payload_select_ops(const struct nft_ctx *ctx,
>  	if (len == 0 || len > FIELD_SIZEOF(struct nft_data, data))
>  		return ERR_PTR(-EINVAL);
>  
> -	if (len <= 4 && IS_ALIGNED(offset, len) && base != NFT_PAYLOAD_LL_HEADER)
> +	if (len <= 4 && IS_ALIGNED(offset, len) &&
> +	    base != NFT_PAYLOAD_LL_HEADER &&
> +	    !(offset & (offset - 1)))

Small cosmetic note: we have is_power_of_2(), which does exactly this.

Also I think the more logical order would be:

len <= 4 && is_power_of_2 && IS_ALIGNED && base ...

>  		return &nft_payload_fast_ops;
>  	else
>  		return &nft_payload_ops;
> -- 
> 1.8.4.2