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From:   Steve Grubb <sgrubb@redhat.com>
To:     Paul Moore <paul@paul-moore.com>
Cc:     mlichvar@redhat.com, omosnace@redhat.com, tglx@linutronix.de,
        linux-audit@redhat.com, rgb@redhat.com, john.stultz@linaro.org,
        sboyd@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH ghak10 v4 0/2] audit: Log modifying adjtimex(2) calls
Date:   Fri, 24 Aug 2018 10:56:19 -0400
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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.

-Steve