On 2020-01-26, at 12:12:51 +0100, Pablo Neira Ayuso wrote:
> I've been looking into (ab)using bitwise to implement add/sub. I would
> like to not add nft_arith for only this, and it seems to me much of
> your code can be reused.
>
> Do you think something like this would work?
Absolutely.
A couple of questions. What's the use-case? I find the combination of
applying the delta to every u32 and having a carry curious. Do you want
to support bigendian arithmetic (i.e., carrying to the left) as well?
I've suggested a couple of changes below.
J.
> Thanks.
>
> diff --git a/include/uapi/linux/netfilter/nf_tables.h
> b/include/uapi/linux/netfilter/nf_tables.h
> index 065218a20bb7..c4078359b6e4 100644
> --- a/include/uapi/linux/netfilter/nf_tables.h
> +++ b/include/uapi/linux/netfilter/nf_tables.h
> @@ -508,11 +508,15 @@ enum nft_immediate_attributes {
> * XOR boolean operations
> * @NFT_BITWISE_LSHIFT: left-shift operation
> * @NFT_BITWISE_RSHIFT: right-shift operation
> + * @NFT_BITWISE_ADD: add operation
> + * @NFT_BITWISE_SUB: subtract operation
> */
> enum nft_bitwise_ops {
> NFT_BITWISE_BOOL,
> NFT_BITWISE_LSHIFT,
> NFT_BITWISE_RSHIFT,
> + NFT_BITWISE_ADD,
> + NFT_BITWISE_SUB,
> };
>
> /**
> diff --git a/net/netfilter/nft_bitwise.c b/net/netfilter/nft_bitwise.c
> index 0ed2281f03be..fd0cd2b4722a 100644
> --- a/net/netfilter/nft_bitwise.c
> +++ b/net/netfilter/nft_bitwise.c
> @@ -60,6 +60,38 @@ static void nft_bitwise_eval_rshift(u32 *dst, const
> u32 *src,
> }
> }
>
> +static void nft_bitwise_eval_add(u32 *dst, const u32 *src,
> + const struct nft_bitwise *priv)
> +{
> + u32 delta = priv->data.data[0];
> + unsigned int i, words;
> + u32 tmp = 0;
> +
> + words = DIV_ROUND_UP(priv->len, sizeof(u32));
> + for (i = 0; i < words; i++) {
> + tmp = src[i];
> + dst[i] = src[i] + delta;
> + if (dst[i] < tmp && i + 1 < words)
> + dst[i + 1]++;
> + }
> +}
for (i = 0; i < words; i++) {
dst[i] = src[i] + delta + tmp;
tmp = dst[i] < src[i] ? 1 : 0;
}
> +static void nft_bitwise_eval_sub(u32 *dst, const u32 *src,
> + const struct nft_bitwise *priv)
> +{
> + u32 delta = priv->data.data[0];
> + unsigned int i, words;
> + u32 tmp = 0;
> +
> + words = DIV_ROUND_UP(priv->len, sizeof(u32));
> + for (i = 0; i < words; i++) {
> + tmp = src[i];
> + dst[i] = src[i] - delta;
> + if (dst[i] > tmp && i + 1 < words)
> + dst[i + 1]--;
> + }
> +}
for (i = 0; i < words; i++) {
dst[i] = src[i] - delta - tmp;
tmp = dst[i] > src[i] ? 1 : 0;
}
> void nft_bitwise_eval(const struct nft_expr *expr,
> struct nft_regs *regs, const struct nft_pktinfo *pkt)
> {
> @@ -77,6 +109,12 @@ void nft_bitwise_eval(const struct nft_expr *expr,
> case NFT_BITWISE_RSHIFT:
> nft_bitwise_eval_rshift(dst, src, priv);
> break;
> + case NFT_BITWISE_ADD:
> + nft_bitwise_eval_add(dst, src, priv);
> + break;
> + case NFT_BITWISE_SUB:
> + nft_bitwise_eval_sub(dst, src, priv);
> + break;
> }
> }
>
> @@ -129,8 +167,8 @@ static int nft_bitwise_init_bool(struct
> nft_bitwise *priv,
> return err;
> }
>
> -static int nft_bitwise_init_shift(struct nft_bitwise *priv,
> - const struct nlattr *const tb[])
> +static int nft_bitwise_init_data(struct nft_bitwise *priv,
> + const struct nlattr *const tb[])
> {
> struct nft_data_desc d;
> int err;
> @@ -191,6 +229,8 @@ static int nft_bitwise_init(const struct nft_ctx
> *ctx,
> case NFT_BITWISE_BOOL:
> case NFT_BITWISE_LSHIFT:
> case NFT_BITWISE_RSHIFT:
> + case NFT_BITWISE_ADD:
> + case NFT_BITWISE_SUB:
> break;
> default:
> return -EOPNOTSUPP;
> @@ -205,7 +245,9 @@ static int nft_bitwise_init(const struct nft_ctx
> *ctx,
> break;
> case NFT_BITWISE_LSHIFT:
> case NFT_BITWISE_RSHIFT:
> - err = nft_bitwise_init_shift(priv, tb);
> + case NFT_BITWISE_ADD:
> + case NFT_BITWISE_SUB:
> + err = nft_bitwise_init_data(priv, tb);
> break;
> }
>
> @@ -226,8 +268,8 @@ static int nft_bitwise_dump_bool(struct sk_buff
> *skb,
> return 0;
> }
>
> -static int nft_bitwise_dump_shift(struct sk_buff *skb,
> - const struct nft_bitwise *priv)
> +static int nft_bitwise_dump_data(struct sk_buff *skb,
> + const struct nft_bitwise *priv)
> {
> if (nft_data_dump(skb, NFTA_BITWISE_DATA, &priv->data,
> NFT_DATA_VALUE, sizeof(u32)) < 0)
> @@ -255,7 +297,9 @@ static int nft_bitwise_dump(struct sk_buff *skb,
> const struct nft_expr *expr)
> break;
> case NFT_BITWISE_LSHIFT:
> case NFT_BITWISE_RSHIFT:
> - err = nft_bitwise_dump_shift(skb, priv);
> + case NFT_BITWISE_ADD:
> + case NFT_BITWISE_SUB:
> + err = nft_bitwise_dump_data(skb, priv);
> break;
> }
>
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