Re: [PATCH nft 0/8] mptcp subtype option match support

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Fri, Nov 19, 2021 at 04:28:39PM +0100, Florian Westphal wrote:
> This series adds 'tcp option mptcp subtype' matching to nft.

LGTM.

> Because the subtype is only 4 bits in size the exthdr
> delinearization needs a fixup to remove the binop added by the
> evaluation step.

By the bitwise operation to take the 4 bits you can infer this refers to
mptcp, but it might be good to store in the rule userdata area that this
expression refers to mptcp as a suggestion to userspace when
delinearizing the rule. I wanted to look into this for a different
usecase.

> One remaining usablility problem is the lack of mnemonics for the
> subtype, i.e. something like:
> 
> static const struct symbol_table mptcp_subtype_tbl = {
>        .base           = BASE_DECIMAL,
>        .symbols        = {
>                SYMBOL("mp-capable",    0),
>                SYMBOL("mp-join",       1),
>                SYMBOL("dss",           2),
>                SYMBOL("add-addr",      3),
>                SYMBOL("remove-addr",   4),
>                SYMBOL("mp-prio",       5),
>                SYMBOL("mp-fail",       6),
>                SYMBOL("mp-fastclose",  7),
>                SYMBOL("mp-tcprst",     8),
>                SYMBOL_LIST_END
>        },
> 
> ... but this would need addition of yet another data type.
>
> Use of implicit/context-dependent symbol table would
> be preferrable, I will look into this next.

Could you develop your idea?

Thanks.