linux-kernel - Re: [PATCH] kernel/time: Make /proc/timer

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Date:	Thu, 18 Nov 2010 09:12:41 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Marcus Meissner <meissner@...e.de>, rusty@...tcorp.com.au,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel/time: Make /proc/timer_list mode 0400


* Thomas Gleixner <tglx@...utronix.de> wrote:

> On Wed, 17 Nov 2010, Andrew Morton wrote:
> 
> > On Wed, 17 Nov 2010 18:18:32 +0100
> > Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > 
> > > On Wed, 2010-11-17 at 18:08 +0100, Marcus Meissner wrote:
> > > > Hi,
> > > > 
> > > > /proc/timer_list contains kernel addresses, like e.g.:
> > > >  #0: <c000000001404158>, tick_sched_timer, S:01, .tick_nohz_restart_sched_tick, swapper/0
> > > >  ...
> > > > 
> > > > Avoid leaking them to user space to make writing kernel exploits a bit harder.
> > > > 
> > > > (I currently cannot think of a userland tool that uses this, this is
> > > > likely pretty much root-only.)
> > > 
> > > iirc powertop parses this..
> > 
> > I bet it doesn't look at the kernel address (why was that added in the
> > first place, anyway?)
> > 
> > I'd suggest that the risk of breakage would be much less if we left the
> > file permissions alone and arranged for those addresses to be
> > 0000000000000000 for non-root readers.
> 
> You beat me to it. Having the full information is quite helpful at
> times.

We should do something like:

	if (!capable(CAP_SYS_ADMIN))
		print_ptr = NULL;

	sprintf(s, "%p", print_ptr);

Thanks,

	Ingo
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