Re: [PATCH nftables 8/8] test: py: add tests for shifted nat port-ranges

[Florian Westphal <fw@strlen.de>]

Pablo Neira Ayuso <pablo@netfilter.org> wrote:

Circling back to this.

> On Fri, Mar 24, 2023 at 11:59:04PM +0100, Florian Westphal wrote:
> > Jeremy Sowden <jeremy@azazel.net> wrote:
> > > +ip daddr 10.0.0.1 tcp dport 55900-55910 dnat ip to 192.168.127.1:5900-5910/55900;ok
> > > +ip6 daddr 10::1 tcp dport 55900-55910 dnat ip6 to [::c0:a8:7f:1]:5900-5910/55900;ok
> > 
> > This syntax is horrible (yes, I know, xtables fault).
> > 
> > Do you think this series could be changed to grab the offset register from the
> > left edge of the range rather than requiring the user to specify it a
> > second time?  Something like:
> > 
> > ip daddr 10.0.0.1 tcp dport 55900-55910 dnat ip to 192.168.127.1:5900-5910
> > 
> > I'm open to other suggestions of course.
> 
> To allow to mix this with maps, I think the best approach is to add a
> new flag (port-shift) and then allow the user to specify the
> port-shift 'delta'.
> 
> ip daddr 10.0.0.1 tcp dport 55900-55910 dnat ip to ip saddr map { \
>         192.168.127.0-129.168.127.128 : 1.2.3.4 . -55000 } port-shift
> 
> where -55000 means, subtract -55000 to the tcp dport in the packet, it
> is an incremental update.
> 
> This requires a kernel patch to add the new port-shift flag.

Where is this new port-shift flag needed?  NAT engine?
I'm a bit confused, are you proposing new/different syntax for Jeremys
kernel-patchset or something else?

AFAICS, for what you want do to, Jeremys kernel patches should
already work as-is?

Just to be clear again, I have no objects to the kernel patches
that Jeremy proposed.  I just dislike the iptables-inspired userspace
syntax with a need to explicitly state the left edge of the range.

> It should be possible to add a new netlink attribute
> 
> NFTA_NAT_REG_PROTO_SHIFT
> 
> which allows for -2^16 .. +2^16 to express the (positive/negative)
> delta offset.

Isn't that essentially what Jeremys patchset is already doing, i.e.
adding a new register to store the offset?

You can't use an immediate, else maps with different deltas don't work.

> Parser would need to be taught to deal with negative and positive
> offset, we probably need a new special type for named maps too
> (port-shift).

You mean a pseudotype to work with 'typeof'? We alreay do this for
verdicts so this should work.