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Date:   Fri, 12 Feb 2021 15:54:40 -0500
From:   Richard Guy Briggs <rgb@redhat.com>
To:     Phil Sutter <phil@nwl.cc>, Steve Grubb <sgrubb@redhat.com>,
        Linux-Audit Mailing List <linux-audit@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        netfilter-devel@vger.kernel.org, Paul Moore <paul@paul-moore.com>,
        Ondrej Mosnacek <omosnace@redhat.com>, fw@strlen.de,
        twoerner@redhat.com, Eric Paris <eparis@parisplace.org>,
        tgraf@infradead.org
Subject: Re: [PATCH ghak124 v3] audit: log nftables configuration change
 events
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On 2021-02-12 13:11, Phil Sutter wrote:
> Hi,
> 
> On Thu, Feb 11, 2021 at 04:02:55PM -0500, Steve Grubb wrote:
> > On Thursday, February 11, 2021 11:29:34 AM EST Paul Moore wrote:
> > > > If I'm not mistaken, iptables emits a single audit log per table, ipset
> > > > doesn't support audit at all. So I wonder how much audit logging is
> > > > required at all (for certification or whatever reason). How much
> > > > granularity is desired?
> >  
> >   <snip> 
> > 
> > > I believe the netfilter auditing was mostly a nice-to-have bit of
> > > functionality to help add to the completeness of the audit logs, but I
> > > could very easily be mistaken.  Richard put together those patches, he
> > > can probably provide the background/motivation for the effort.
> > 
> > There are certifications which levy requirements on information flow control. 
> > The firewall can decide if information should flow or be blocked. Information 
> > flow decisions need to be auditable - which we have with the audit target. 
> 
> In nftables, this is realized via 'log level audit' statement.
> Functionality should by all means be identical to that of xtables' AUDIT
> target.
> 
> > That then swings in requirements on the configuration of the information flow 
> > policy.
> > 
> > The requirements state a need to audit any management activity - meaning the 
> > creation, modification, and/or deletion of a "firewall ruleset". Because it 
> > talks constantly about a ruleset and then individual rules, I suspect only 1 
> > summary event is needed to say something happened, who did it, and the 
> > outcome. This would be in line with how selinux is treated: we have 1 summary 
> > event for loading/modifying/unloading selinux policy.
> 
> So the central element are firewall rules for audit purposes and
> NETFILTER_CFG notifications merely serve asserting changes to those
> rules are noticed by the auditing system. Looking at xtables again, this
> seems coherent: Any change causes the whole table blob to be replaced
> (while others stay in place). So table replace/create is the most common
> place for a change notification. In nftables, the most common one is
> generation dump - all tables are treated as elements of the same
> ruleset, not individually like in xtables.
> 
> Richard, assuming the above is correct, are you fine with reducing
> nftables auditing to a single notification per transaction then? I guess
> Florian sufficiently illustrated how this would be implemented.

Yes, that should be possible.

> > Hope this helps...
> 
> It does, thanks a lot for the information!
> 
> Thanks, Phil

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635