linux-kernel - Re: [PATCH] prevent timespec/timeval to ktime

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Date:	Thu, 31 Aug 2006 00:05:02 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Frank v Waveren <fvw@....cx>
Cc:	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] prevent timespec/timeval to ktime_t overflow

On Wed, 2006-08-30 at 23:44 +0200, Frank v Waveren wrote:
> On Wed, Aug 30, 2006 at 10:44:28AM +0200, Thomas Gleixner wrote:
> > Frank v. Waveren pointed out that on 64bit machines the timespec to
> > ktime_t conversion might overflow. This is also true for timeval to
> > ktime_t conversions. This breaks a "sleep inf" on 64bit machines.
> ...
> > Check the seconds argument to the conversion and limit it to the maximum
> > time which can be represented by ktime_t.
> 
> It's a solution, and it more or less fixes things without any changes
> to userspace, which is nice. I still prefer my patch in
> <20060827083438.GA6931@....cx> though, possibly with modifications so
> it doesn't affect all timespec users but only nanosleep (we'd have to
> check if the other timespec users aren't converting to ktime_t). 
> 
> With this patch, we sleep shorter than specified, and don't signal
> this in any way. Returning EINVAL for anything except negative tv_sec
> or invalid tv_nsec breaks the spec too, but I prefer errors to
> silently sleeping too short.

I really don't care whether we sleep 100 or 5000 years in the case of
"sleep MAX_LONG"

> I'll grant this is more of an aesthetic point than something that'll
> cause real-world problems (300 years is a long time for any sleep),
> but if things break I like them to do so as loudly as possible, as a
> general rule.

One thing you ignore is that your patch does not cure the introduced
user space breakage, it just replaces the overflow caused very short
sleep by a return -EINVAL, which is breaking existing userspace in a
different way. We have to preserve user space interfaces even when they
violate your aesthetic well-being.

	tglx


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