linux-kernel - Re: [RFC PATCH ghak10 v4 0/2] audit: Log modifying adjtimex(2) calls

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Date:   Thu, 13 Sep 2018 10:07:54 -0400
From:   Steve Grubb <sgrubb@...hat.com>
To:     Ondrej Mosnacek <omosnace@...hat.com>
Cc:     Paul Moore <paul@...l-moore.com>,
        Miroslav Lichvar <mlichvar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux-Audit Mailing List <linux-audit@...hat.com>,
        Richard Guy Briggs <rgb@...hat.com>,
        John Stultz <john.stultz@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH ghak10 v4 0/2] audit: Log modifying adjtimex(2) calls

On Thursday, September 13, 2018 9:58:32 AM EDT Ondrej Mosnacek wrote:
> On Fri, Aug 24, 2018 at 4:56 PM Steve Grubb <sgrubb@...hat.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@...hat.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? :)

I do not think its important to record the errors since the exit code tells 
us there's a problem. IOW, I'm agreeing with Paul.

-Steve