linux-kernel - Re: [PATCH ghak10 v5 2/2] timekeeping/ntp: Audit clock/NTP params adjustments

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Message-ID: <alpine.DEB.2.21.1808272341370.1359@nanos.tec.linutronix.de>
Date:   Mon, 27 Aug 2018 23:42:38 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Miroslav Lichvar <mlichvar@...hat.com>
cc:     Ondrej Mosnacek <omosnace@...hat.com>,
        Richard Guy Briggs <rgb@...hat.com>,
        Linux-Audit Mailing List <linux-audit@...hat.com>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH ghak10 v5 2/2] timekeeping/ntp: Audit clock/NTP params
 adjustments

On Mon, 27 Aug 2018, Miroslav Lichvar wrote:

> On Mon, Aug 27, 2018 at 01:35:09PM +0200, Ondrej Mosnacek wrote:
> > On Fri, Aug 24, 2018 at 9:51 PM Richard Guy Briggs <rgb@...hat.com> wrote:
> > > It appears this time_tai use of "constant" is different than
> > > time_constant, the former not mentioned by Miroslav Lichvar.  What is it
> > > and is it important to log for security?  It sounds like it is
> > > important.
> 
> > The TAI offset is the offset of the clock from the International
> > Atomic Time, so basically the time zone offset. I suppose it can't
> > influence the audit timestamps, but changing timezones can still cause
> > all sorts of confusion throughout the system, so intuitively I would
> > say we should log it.
> 
> It's not related to timezones. ADJ_TAI sets the offset of the system
> TAI clock (CLOCK_TAI) relative to the standard UTC clock
> (CLOCK_REALTIME). CLOCK_TAI is rarely used by applications. Setting
> the TAI offset effectively injects a whole-second offset to the TAI
> time. 

Rarely used today, but with TSN it's going to get more usage in not so
distant future.

Thanks,

	tglx