linux-kernel - Re: [tip:timers/core] ntp: Fix integer overflow when setting time

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Date:	Fri, 16 Mar 2012 10:48:02 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	mingo@...hat.com, levinsasha928@...il.com,
	linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:timers/core] ntp: Fix integer overflow when setting time

On Thu, 15 Mar 2012, H. Peter Anvin wrote:

> On 03/15/2012 02:53 PM, tip-bot for Sasha Levin wrote:
> > Commit-ID:  a078c6d0e6288fad6d83fb6d5edd91ddb7b6ab33
> > Gitweb:     http://git.kernel.org/tip/a078c6d0e6288fad6d83fb6d5edd91ddb7b6ab33
> > Author:     Sasha Levin <levinsasha928@...il.com>
> > AuthorDate: Thu, 15 Mar 2012 12:36:14 -0400
> > Committer:  Thomas Gleixner <tglx@...utronix.de>
> > CommitDate: Thu, 15 Mar 2012 21:41:34 +0100
> > 
> > ntp: Fix integer overflow when setting time
> > 
> > 'long secs' is passed as divisor to div_s64, which accepts a 32bit
> > divisor. On 64bit machines that value is trimmed back from 8 bytes
> > back to 4, causing a divide by zero when the number is bigger than
> > (1 << 32) - 1 and all 32 lower bits are 0.
> > 
> > Use div64_long() instead.
> > 
> 
> Perhaps we should use the same kind of multiply-and-shift tricks we're
> doing for jiffies conversion?  If nothing else it ought to perform better.

It's not a hotpath where performance matters, but divide by zero does :)
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