Re: [PATCH nf-next v4 00/10] netfilter: nft_bitwise: shift support

[Jeremy Sowden <jeremy@azazel.net>]

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On 2020-01-16, at 13:09:25 +0100, Pablo Neira Ayuso wrote:
> On Thu, Jan 16, 2020 at 11:41:53AM +0000, Jeremy Sowden wrote:
> > On 2020-01-16, at 12:22:47 +0100, Pablo Neira Ayuso wrote:
> > > On Thu, Jan 16, 2020 at 08:51:33AM +0000, Jeremy Sowden wrote:
> > > > On 2020-01-15, at 21:32:06 +0000, Jeremy Sowden wrote:
> > > > > The connmark xtables extension supports bit-shifts.  Add support
> > > > > for shifts to nft_bitwise in order to allow nftables to do
> > > > > likewise, e.g.:
> > > > >
> > > > >   nft add rule t c oif lo ct mark set meta mark << 8 | 0xab
> > > > >   nft add rule t c iif lo meta mark & 0xff 0xab ct mark set meta mark >> 8
> > > > >
> > > > > Changes since v3:
> > > > >
> > > > >   * the length of shift values sent by nft may be less than
> > > > >   sizeof(u32).
> > > >
> > > > Actually, having thought about this some more, I believe I had it
> > > > right in v3.  The difference between v3 and v4 is this:
> > > >
> > > >   @@ -146,7 +146,7 @@ static int nft_bitwise_init_shift(struct nft_bitwise *priv,
> > > >                               tb[NFTA_BITWISE_DATA]);
> > > >           if (err < 0)
> > > >                   return err;
> > > >   -       if (d.type != NFT_DATA_VALUE || d.len != sizeof(u32) ||
> > > >   +       if (d.type != NFT_DATA_VALUE || d.len > sizeof(u32) ||
> > > >               priv->data.data[0] >= BITS_PER_TYPE(u32)) {
> > >
> > > Why restrict this to 32-bits?
> >
> > Because of how I implemented the shifts.  Here's the current rshift:
> >
> >   static void nft_bitwise_eval_rshift(u32 *dst, const u32 *src,
> >                                       const struct nft_bitwise *priv)
> >   {
> >           u32 shift = priv->data.data[0];
> >           unsigned int i;
> >           u32 carry = 0;
> >
> >           for (i = 0; i < DIV_ROUND_UP(priv->len, sizeof(u32)); i++) {
> >                   dst[i] = carry | (src[i] >> shift);
> >                   carry = src[i] << (BITS_PER_TYPE(u32) - shift);
> >           }
> >   }
> >
> > In order to support larger shifts, it would need to look something
> > like:
>
> No need for larger shift indeed, no need for this.
>
> I just wanted to make sure NFTA_BITWISE_DATA can be reused later on in
> future new operation that might require larger data.
>
> All good then, I'll review v3, OK?

Yup. :)

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