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From:   Ondrej Mosnacek <omosnace@redhat.com>
Date:   Thu, 13 Sep 2018 15:58:32 +0200
Message-ID: <CAFqZXNtsjAt3ks7L=e24UVhx23bihz1MLN7gKihs=LFJDShutg@mail.gmail.com>
Subject: Re: [RFC PATCH ghak10 v4 0/2] audit: Log modifying adjtimex(2) calls
To:     Steve Grubb <sgrubb@redhat.com>
Cc:     Paul Moore <paul@paul-moore.com>,
        Miroslav Lichvar <mlichvar@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux-Audit Mailing List <linux-audit@redhat.com>,
        Richard Guy Briggs <rgb@redhat.com>,
        John Stultz <john.stultz@linaro.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Linux kernel mailing list <linux-kernel@vger.kernel.org>
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On Fri, Aug 24, 2018 at 4:56 PM Steve Grubb <sgrubb@redhat.com> wrote:
> On Wednesday, August 22, 2018 5:27:17 PM EDT Paul Moore wrote:
> > On Tue, Aug 21, 2018 at 3:21 AM Miroslav Lichvar <mlichvar@redhat.com>
> wrote:
> > > > On Mon, 20 Aug 2018, Ondrej Mosnacek wrote:
> > > > > @John or other timekeeping/NTP folks: We had a discussion on the
> > > > > audit
> > > > > ML on which of the internal timekeeping/NTP variables we should
> > > > > actually
> > > > > log changes for. We are only interested in variables that can
> > > > > (directly
> > > > > or indirectly) cause noticeable changes to the system clock, but
> > > > > since we
> > > > > have only limited understanding of the NTP code, we would like to ask
> > > > > you for advice on which variables are security relevant.
> > >
> > > I guess that mostly depends on whether you consider setting the clock
> > > to run faster or slower than real time to be an important event for
> > > the audit.
> > >
> > > > > - NTP value adjustments:
> > > > > - time_offset (probably important)
> > >
> > > This can adjust the clock by up to 0.5 seconds per call and also speed
> > > it up or slow down by up to about 0.05% (43 seconds per day).
> >
> > This seems worthwhile.
> >
> > > > > - time_freq (maybe not important?)
> > >
> > > This can speed up or slow down by up to about 0.05%.
> >
> > This too.
> >
> > > > > - time_status (likely important, can cause leap second injection)
> > >
> > > Yes, it can insert/delete leap seconds and it also enables/disables
> > > synchronization of the hardware real-time clock.
> >
> > This one as well.
> >
> > > > > - time_maxerror (maybe not important?)
> > > > > - time_esterror (maybe not important?)
> > >
> > > These two change the error estimates that are reported to applications
> > > using ntp_gettime()/adjtimex(). If an application was periodically
> > > checking that the clock is synchronized with some specified accuracy
> > > and setting the maxerror to a larger value would cause the application
> > > to abort, would it be an important event in the audit?
> >
> > Since these don't really affect the time, just the expected error, I'm
> > not sure this is important.
>
> I don't think so.

Sorry, just to make sure I understand it right - do you (also) not
think it is important or do you not think it is not important? :)

--
Ondrej Mosnacek <omosnace at redhat dot com>
Associate Software Engineer, Security Technologies
Red Hat, Inc.