linux-kernel - Re: [PATCH ghak10 v5 1/2] audit: Add functions to log time adjustments

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Date:   Mon, 27 Aug 2018 12:38:09 -0400
From:   Steve Grubb <sgrubb@...hat.com>
To:     Ondrej Mosnacek <omosnace@...hat.com>
Cc:     Miroslav Lichvar <mlichvar@...hat.com>,
        Linux-Audit Mailing List <linux-audit@...hat.com>,
        Paul Moore <paul@...l-moore.com>,
        Richard Guy Briggs <rgb@...hat.com>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH ghak10 v5 1/2] audit: Add functions to log time adjustments

On Monday, August 27, 2018 5:13:17 AM EDT Ondrej Mosnacek wrote:
> On Mon, Aug 27, 2018 at 9:50 AM Miroslav Lichvar <mlichvar@...hat.com> 
wrote:
> > On Fri, Aug 24, 2018 at 02:00:00PM +0200, Ondrej Mosnacek wrote:
> > > This patch adds two auxiliary record types that will be used to
> > > annotate
> > > the adjtimex SYSCALL records with the NTP/timekeeping values that have
> > > been changed.
> > 
> > It seems the "adjust" function intentionally logs also calls/modes
> > that don't actually change anything. Can you please explain it a bit
> > in the message?
> > 
> > NTP/PTP daemons typically don't read the adjtimex values in a normal
> > operation and overwrite them on each update, even if they don't
> > change. If the audit function checked that oldval != newval, the
> > number of messages would be reduced and it might be easier to follow.
> 
> We actually want to log any attempt to change a value, as even an
> intention to set/change something could be a hint that the process is
> trying to do something bad (see discussion at [1]).

One of the problems is that these applications can flood the logs very 
quickly. An attempt to change is not needed unless it fails for permissions 
reasons. So, limiting to actual changes is probably a good thing.

-Steve

> There are valid
> arguments both for and against this choice, but we have to pick one in
> the end... Anyway, I should explain the reasoning in the commit
> message better, right now it just states the fact without explanation
> (in the second patch), thank you for pointing my attention to it.
> 
> [1] https://www.redhat.com/archives/linux-audit/2018-July/msg00061.html
> 
> --
> Ondrej Mosnacek <omosnace at redhat dot com>
> Associate Software Engineer, Security Technologies
> Red Hat, Inc.