linux-kernel - Re: [PATCH] mm: Fix dirty_bytes/dirty_background

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Message-ID: <alpine.LNX.2.00.0902011036470.6140@titan.stealer.net>
Date:	Sun, 1 Feb 2009 11:22:40 +0100 (CET)
From:	Sven Wegener <sven.wegener@...aler.net>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Chinner <david@...morbit.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Fix dirty_bytes/dirty_background_bytes sysctls on
 64bit arches

On Sun, 1 Feb 2009, Peter Zijlstra wrote:

> On Sun, 2009-02-01 at 02:22 +0100, Sven Wegener wrote:
> > We need to pass an unsigned long as the minimum, because it gets casted
> > to an unsigned long in the sysctl handler. If we pass an int, we'll
> > access four more bytes on 64bit arches, resulting in a random minimum
> > value.
> 
> If that's so, how can any of those other limit values still be good?

The problem here is that we use proc_doulongvec_minmax(), which expects an 
unsigned long. Most other sysctls use the dointvec versions and are safe, 
as long as they pass an int. If they pass a char or a short, they're 
subject to the same problem.

The other sysctls in sysctl.c that use proc_doulongvec_minmax() don't pass 
a min/max value. The others in the kernel I checked do the same or pass a 
proper unsigned long.

Sven
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