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Date:   Mon, 27 Aug 2018 23:42:38 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Miroslav Lichvar <mlichvar@redhat.com>
cc:     Ondrej Mosnacek <omosnace@redhat.com>,
        Richard Guy Briggs <rgb@redhat.com>,
        Linux-Audit Mailing List <linux-audit@redhat.com>,
        Linux kernel mailing list <linux-kernel@vger.kernel.org>,
        Stephen Boyd <sboyd@kernel.org>,
        John Stultz <john.stultz@linaro.org>
Subject: Re: [PATCH ghak10 v5 2/2] timekeeping/ntp: Audit clock/NTP params
 adjustments
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References: <20180824120001.20771-1-omosnace@redhat.com> <20180824120001.20771-3-omosnace@redhat.com> <20180824194703.h3mbuhrxzixmna4e@madcap2.tricolour.ca> <CAFqZXNvD_7psR+wM-GTXQ4bwK3w8=t7UnBidojB5XbmbE_K2oA@mail.gmail.com>
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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@redhat.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