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

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Message-Id: <20110107195016.2334940467@magilla.sf.frob.com>
Date:	Fri,  7 Jan 2011 11:50:16 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...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.

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

This is constrained by ptrace_may_access(task, PTRACE_MODE_READ).

> And /proc/schedstat shows sum_exec_runtime.

This probably should be constrained in exactly the same ways as .../stat is.

I think the constraints on /proc/.../stat reflect the most considered
judgement of the security folks.  I suspect that the lack of constraint on
/proc/.../schedstat reflects the scheduler folks just having failed to
consider the same issues.  IMHO all access to the equivalent kinds of
information should have the same security constraints.

> 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().

That's good, but it should be mentioned so that next year someone doesn't
come back with a "there's no reason you shouldn't be able to" and go
unchallenged.

Thanks,
Roland
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