linux-kernel - Re: kernel/time/ntp.c: Possible off-by-one error in TAI range check?

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Message-ID: <CAFqZXNuqWGNwUTUxWjZRmx4PFL2zsRRo6fu+ZXZwaQAMvuf1kQ@mail.gmail.com>
Date:   Mon, 15 Apr 2019 10:02:54 +0200
From:   Ondrej Mosnacek <omosnace@...hat.com>
To:     Roman Zippel <zippel@...ux-m68k.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <john.stultz@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: kernel/time/ntp.c: Possible off-by-one error in TAI range check?

On Mon, Apr 8, 2019 at 10:47 AM Ondrej Mosnacek <omosnace@...hat.com> wrote:
> Hello,
>
> while writing tests for clock adjustment auditing [1] [2], I stumbled
> upon a strange behavior of adjtimex(2) when setting the TAI offset...
>
> Commit 153b5d054ac2 ("ntp: support for TAI") added a possibility to
> change the TAI offset from userspace via adjtimex(2). The code checks
> if the input value (txc->constant) is greater than 0 and if it is not,
> then it doesn't modify the value. Ignoring the fact that this check
> should probably be in timekeeping_validate_timex() and cause -EINVAL
> to be returned when false, I find it strange that the check doesn't
> allow to set the value to 0, which seems to be the default value...
>
> Was this behavior intended or should the code actually check for
> txc->constant >= 0 instead of txc->constant > 0?

Ping?

>
> Thanks,
>
> [1] https://github.com/linux-audit/audit-kernel/issues/10
> [2] https://github.com/linux-audit/audit-kernel/wiki/RFE-More-detailed-auditing-of-changes-to-system-clock
>
> --
> Ondrej Mosnacek <omosnace at redhat dot com>
> Software Engineer, Security Technologies
> Red Hat, Inc.

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