Re: [nf-next PATCH v2] netfilter: nf_tables: Introduce NFTA_RULE_ACTUAL_EXPR

[Phil Sutter <phil@nwl.cc>]

On Thu, Apr 27, 2023 at 01:01:55PM +0200, Pablo Neira Ayuso wrote:
> On Thu, Apr 27, 2023 at 12:57:30PM +0200, Phil Sutter wrote:
> > Hi Pablo,
> > 
> > On Wed, Apr 26, 2023 at 09:58:44PM +0200, Pablo Neira Ayuso wrote:
> > [...]
> > > My proposal:
> > 
> > Thanks for returning to this. Your approach requires to define a minimum
> > version from which on forward-compat is guaranteed. I was trying to
> > avoid this requirement though so things would work for "unknown user
> > space".
> 
> You also require a kernel that supports your approach.

Sure. But in the described use-case, anything but old user space (i.e.,
container content) is under control.

> > Currently, the only offending extension is ebt_among since it doesn't
> > exist (and never did) in non-native form. If I implement among extension
> > parsing (even in non-functional form), my original approach would work.
> > This also means having a minimum version for full compat, but it affects
> > ebtables (actually, use of ebt_among) only.
> 
> Yes, but this is fully user data, kernel really does not need to do
> anything with this alternative representation, which is what I do not
> like from you proposal.

OK.

> I really think userdata is the place to deal with this.

Having to touch old user space is not a good solution for the given
use-case. If kernel modification is a no-go, I'd rather introduce a
"compat mode" in iptables-nft which causes rule creation in the most
compatible form. This might impact run-time performance but is much
simpler to implement and maintain.

Cheers, Phil