Re: does nftables support string match?

[Florian Westphal <fw@strlen.de>]

Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> Cc'ing Florian,
> 
> On Wed, Sep 13, 2017 at 08:13:38PM +0800, Michael Chi wrote:
> > Hi experts,
> > 
> > We are using nftables instead of iptables, but after I have search all
> > the nftables documents I found, I don't find a corresponding match
> > that can match string in packet, like following in iptables:
> > iptables -A INPUT -m string --string 'badstring' -j DROP
> > 
> > Is such function supported by nftables?
> 
> I remember he's got a patch to add support for this, still to be
> upstreamed.

The decision at nfws was to not upstream this, iirc, due to the fact
that this mandates linear evaluation.  Instead we talked about adding
application offset.

> Moreover, I started on a patchset to add a new application layer
> offset that we discussed during NFWS:
> 
> https://workshop.netfilter.org/2017/wiki/images/8/8c/Nft-l7.pdf
> 
> So we can solve the existing limitation in iptables, since we start
> matching after IP header offset.

Right.  IIRC you also planned to add some way to describe the userspace
headers including ability to skip variable-sized content or search for
a start-marker so one could e.g. move to a particular offset and then
extract content.

This would allow to combine it with set lookups, and just have a set of
strings to do a lookup in.

Michael, what are you trying to match? dns lookups? tls sni hostname?