linux-kernel - Re: [PATCH] CPU online file permission

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Message-Id: <20070730165720.37780cc6.akpm@linux-foundation.org>
Date:	Mon, 30 Jul 2007 16:57:20 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ulrich Drepper <drepper@...hat.com>
Cc:	linux-kernel@...r.kernel.org, stable@...nel.org,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] CPU online file permission

On Sun, 29 Jul 2007 20:56:46 -0400
Ulrich Drepper <drepper@...hat.com> wrote:

> Is there a reason why the "online" file in the subdirectories for the CPUs
> in /sys/devices/system isn't world-readable?

No sane one which I can think of.  It seems that it originally sprang forth
from Rusty's keyboard in that form.

>  I cannot imagine it to be
> security relevant especially now that a getcpu() syscall can be used to
> determine what CPUa  thread runs on.
> 
> The file is useful to correctly implement the sysconf() function to return
> the number of online CPUs.  In the presence of hotplug we currently cannot
> provide this information.  The patch below should to it.
> 
> 
> Signed-off-by: Ulrich Drepper <drepper@...hat.com>
> 
> --- drivers/base/cpu.c	2007-02-20 12:01:31.000000000 -0800
> +++ drivers/base/cpu.c-new	2007-07-29 17:52:58.000000000 -0700
> @@ -53,7 +53,7 @@
>  		ret = count;
>  	return ret;
>  }
> -static SYSDEV_ATTR(online, 0600, show_online, store_online);
> +static SYSDEV_ATTR(online, 0644, show_online, store_online);
>  
>  static void __devinit register_cpu_control(struct cpu *cpu)
>  {

I'll pass this by the -stable guys too - I assume we'd like it fixed in
2.6.22 (or earlier) as well..

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