linux-kernel - Re: [PATCH ghak124 v3] audit: log nftables configuration change events

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Date:   Fri, 12 Feb 2021 13:11:12 +0100
From:   Phil Sutter <phil@....cc>
To:     Steve Grubb <sgrubb@...hat.com>
Cc:     Richard Guy Briggs <rgb@...hat.com>,
        Linux-Audit Mailing List <linux-audit@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        netfilter-devel@...r.kernel.org, Paul Moore <paul@...l-moore.com>,
        Ondrej Mosnacek <omosnace@...hat.com>, fw@...len.de,
        twoerner@...hat.com, Eric Paris <eparis@...isplace.org>,
        tgraf@...radead.org
Subject: Re: [PATCH ghak124 v3] audit: log nftables configuration change
 events

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.

> Hope this helps...

It does, thanks a lot for the information!

Thanks, Phil