linux-kernel - Re: [RFC][PATCH] timekeeping: Limit system time to prevent 32-bit time

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Message-ID: <20150416075450.GY32271@localhost>
Date:	Thu, 16 Apr 2015 09:54:50 +0200
From:	Miroslav Lichvar <mlichvar@...hat.com>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org, John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Prarit Bhargava <prarit@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [RFC][PATCH] timekeeping: Limit system time to prevent 32-bit
 time_t overflow

On Wed, Apr 15, 2015 at 10:31:54PM +0100, One Thousand Gnomes wrote:
> On Wed, 15 Apr 2015 17:41:28 +0200
> Miroslav Lichvar <mlichvar@...hat.com> wrote:
> > larger value. When the maximum is reached in normal time accumulation,
> > the clock will be stepped back by one week.
> 
> Which itself is open to exploits and dirty tricks and causes bizarre
> problems.

Any examples? I think it shouldn't be any worse than having system
clock with incorrect time and making a backward step, which is a well
understood problem.

> IMHO it doesn't actually improve the situation.

Do you have a 32-bit system for testing? Try "date -s @2147483600",
wait one minute and see if it's not worth preventing.

I think the power consumption alone is worth it. If there is some
widely used application/service in which the overflow triggers an
infinite loop making requests to a network service, maybe it could
prevent a DDoS attack.

-- 
Miroslav Lichvar
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