linux-kernel - Re: [PATCH] time: Improve sanity checking of timekeeping inputs

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Date:	Wed, 15 Aug 2012 07:39:19 -0400
From:	Josh Boyer <jwboyer@...il.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Prarit Bhargava <prarit@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Zhouping Liu <zliu@...hat.com>, CAI Qian <caiqian@...hat.com>,
	Sasha Levin <levinsasha928@...il.com>, stable@...r.kernel.org
Subject: Re: [PATCH] time: Improve sanity checking of timekeeping inputs

On Wed, Aug 8, 2012 at 3:36 PM, John Stultz <john.stultz@...aro.org> wrote:
> Thomas, Ingo,
>         Here's a fix against tip/timers/urgent that addresses
> timekeeping edge cases detected by both a bad BIOS and system
> fuzzing w/ trinity. Thanks to Sasha Levin and CAI Qian for
> finding and reporting these!
>
> Let me know if you have any tweaks you want to see.
>
> thanks
> -john
>
> Unexpected behavior could occur if the time is set to
> a value large enough to overflow a 64bit ktime_t
> (which is something larger then the year 2262).
>
> Also unexpected behavior could occur if large negative
> offsets are injected via adjtimex.
>
> So this patch improves the sanity check timekeeping inputs
> by improving the timespec_valid() check, and then makes better
> use of timespec_valid() to make sure we don't set the time to
> an invalid negative value or one that overflows ktime_t.
>
> Note: This does not protect from setting the time close to
> overflowing ktime_t and then letting natural accumulation
> cause the overflow.
>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Prarit Bhargava <prarit@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Zhouping Liu <zliu@...hat.com>
> Cc: CAI Qian <caiqian@...hat.com>
> Cc: Sasha Levin <levinsasha928@...il.com>
> Cc: stable@...r.kernel.org
> Reported-by: CAI Qian <caiqian@...hat.com>
> Reported-by: Sasha Levin <levinsasha928@...il.com>
> Signed-off-by: John Stultz <john.stultz@...aro.org>
> ---
>  include/linux/ktime.h     |    7 -------
>  include/linux/time.h      |   22 ++++++++++++++++++++--
>  kernel/time/timekeeping.c |   26 ++++++++++++++++++++++++--
>  3 files changed, 44 insertions(+), 11 deletions(-)

This patch fixes a boot regression on machines with crappy BIOS.  Is
this going to get committed soon?

https://bugzilla.redhat.com/show_bug.cgi?id=844249

josh
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