linux-kernel - Re: [PATCH] Read THREAD_CPUTIME clock from other processes.

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Message-ID: <20110107193547.GA28634@redhat.com>
Date:	Fri, 7 Jan 2011 20:35:47 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Dario Faggioli <raistlin@...ux.it>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	torbenh <torbenh@....de>, john.stultz@...aro.org,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] Read THREAD_CPUTIME clock from other  processes.

On 01/07, Roland McGrath wrote:
>
> This can certainly be enhanced, but it opens some cans of worms about the
> security question.  It is probably still considered an unsafe information
> leak to let every process examine every other process's thread clocks.

Yes, I was worried about possible security issues too. But, it seems,
/proc/pid/task/tid/stat (do_task_stat) shows ->utime/stime anyway.
And /proc/schedstat shows sum_exec_runtime.

> I'll leave that judgement to security folks.

Agreed.

> As well as the information leak, it is most certainly a DoS attack vector
> to allow one process to set CPU timers an another process or its threads.

No, the suggested change doesn't go that far, afaics. It only modifies
check_clock: this affects clock_getres and clock_set (which does nothing),
and posix_cpu_clock_get: affects clock_gettime().

Oleg.

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