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From: Richard Cochran <richardcochran@gmail.com>
To: John Stultz <john.stultz@linaro.org>
Cc: lkml <linux-kernel@vger.kernel.org>,
	Vegard Nossum <vegard.nossum@oracle.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>,
	Prarit Bhargava <prarit@redhat.com>
Subject: Re: [PATCH 4/6] time: Avoid undefined behaviour in timespec64_add_safe()
Date: Thu, 1 Sep 2016 10:02:55 +0200	[thread overview]
Message-ID: <20160901080255.GA2386@localhost.localdomain> (raw)
In-Reply-To: <1472680222-21060-5-git-send-email-john.stultz@linaro.org>

On Wed, Aug 31, 2016 at 02:50:20PM -0700, John Stultz wrote:
>     UBSAN: Undefined behaviour in kernel/time/time.c:783:2
>     signed integer overflow:
>     5273 + 9223372036854771711 cannot be represented in type 'long int'

...

> Line 783 is this:
> 
> 783         set_normalized_timespec64(&res, lhs.tv_sec + rhs.tv_sec,
> 784                         lhs.tv_nsec + rhs.tv_nsec);

...

> Note that this is not currently a huge concern since the kernel should be
> built with -fno-strict-overflow by default, but could be a problem in the
> future, a problem with older compilers, or other compilers than gcc.

Is this really a concern at all?  The value 9223372036854771711 is a
huge number of seconds.

Thanks,
Richard

  reply	other threads:[~2016-09-01  8:04 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-31 21:50 [GIT PULL][PATCH 0/6] 4.9 timekeeping changes for tip/timers/core John Stultz
2016-08-31 21:50 ` [PATCH 1/6] hrtimer: Spelling fixes John Stultz
2016-08-31 21:50 ` [PATCH 2/6] clocksource: Defer override invalidation unless clock is unstable John Stultz
2016-08-31 21:50 ` [PATCH 3/6] timekeeping: Prints the amounts of time spent during suspend John Stultz
2016-08-31 21:50 ` [PATCH 4/6] time: Avoid undefined behaviour in timespec64_add_safe() John Stultz
2016-09-01  8:02   ` Richard Cochran [this message]
2016-09-01  9:37     ` Vegard Nossum
2016-08-31 21:50 ` [PATCH 5/6] time: Avoid undefined behaviour in ktime_add_safe() John Stultz
2016-08-31 21:50 ` [PATCH 6/6] time: alarmtimer: Add tracepoints for alarmtimers John Stultz

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