From: John Stultz <john.stultz@linaro.org>
To: Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Arjan van de Ven <arjan@linux.intel.com>
Cc: lkml <linux-kernel@vger.kernel.org>,
John Stultz <john.stultz@linaro.org>,
Oren Laadan <orenl@cellrox.com>,
Ruchi Kandoi <kandoiruchi@google.com>,
Rom Lemarchand <romlem@android.com>,
Kees Cook <keescook@chromium.org>,
Android Kernel Team <kernel-team@android.com>,
Todd Kjos <tkjos@google.com>, Colin Cross <ccross@android.com>,
Nick Kralevich <nnk@google.com>,
Dmitry Shmidt <dimitrysh@google.com>,
Elliott Hughes <enh@google.com>
Subject: Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface
Date: Wed, 13 Jul 2016 16:47:15 -0700 [thread overview]
Message-ID: <CALAqxLUsJ8Aph76mJ9xZWry56xvL8wKy+HVbgh=NQ-fimFUtJg@mail.gmail.com> (raw)
In-Reply-To: <1455671191-32105-3-git-send-email-john.stultz@linaro.org>
On Tue, Feb 16, 2016 at 5:06 PM, John Stultz <john.stultz@linaro.org> wrote:
> This patch provides a proc/PID/timerslack_ns interface which
> exposes a task's timerslack value in nanoseconds and allows it
> to be changed.
>
> This allows power/performance management software to set timer
> slack for other threads according to its policy for the thread
> (such as when the thread is designated foreground vs. background
> activity)
>
> If the value written is non-zero, slack is set to that value.
> Otherwise sets it to the default for the thread.
>
> This interface checks that the calling task has permissions to
> to use PTRACE_MODE_ATTACH_FSCREDS on the target task, so that we
> can ensure arbitrary apps do not change the timer slack for other
> apps.
Sigh.
So I wanted to pull this thread up again, because when I originally
proposed upstreaming the PR_SET_TIMERSLACK_PID feature from the AOSP
common.git tree, the first objection from Arjan was that it only
required CAP_SYS_NICE:
http://lkml.iu.edu/hypermail/linux/kernel/1506.3/01491.html
And reasonably, setting timerslack to very large values does have the
potential to effect applications much further then what a task could
do previously with CAP_SYS_NICE.
CAP_SYS_PTRACE was suggested instead, as that allows applications to
manipulate other tasks more drastically.
(At the time, I checked with some of the Android developers, and got
no objection to changing to use this capability.)
However, after submitting the changes to Android required to support
the upstreamed /proc/<tid>/timerslack_ns interface, I've gotten some
objections with adding CAP_SYS_PTRACE to the system_server, as this
would allow the system_server to be able to inspect and modify memory
on any task in the system. This gives the system_server privileged to
effect applications much further then what it could do previously.
So I worry I'm a bit stuck here. For general systems, CAP_SYS_NICE is
too low a level of privilege to set a tasks timerslack, but
apparently CAP_SYS_PTRACE is too high a privilege for Android's
system_server to require just to set a tasks timerslack value.
So I wanted to ask again if we might consider backing this down to
CAP_SYS_NICE, or if we can instead introduce a new CAP_SYS_TIMERSLACK
or something to provide the needed in-between capability level.
Thoughts?
thanks
-john
next prev parent reply other threads:[~2016-07-13 23:47 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-17 1:06 [PATCH 0/2] Extend timer_slack_ns to u64 on 32bit systems & add /proc/<pid>/timerslack_ns John Stultz
2016-02-17 1:06 ` [PATCH 1/2] timer: Convert timer_slack_ns from unsigned long to u64 John Stultz
2016-02-17 1:06 ` [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface John Stultz
2016-02-17 19:35 ` Andrew Morton
2016-02-17 20:09 ` Kees Cook
2016-02-17 20:18 ` Andrew Morton
2016-02-17 20:51 ` John Stultz
2016-02-17 21:07 ` Andrew Morton
2016-02-17 22:29 ` John Stultz
2016-02-17 22:45 ` Kees Cook
2016-02-17 22:51 ` John Stultz
2016-02-17 22:53 ` Andrew Morton
2016-02-17 20:49 ` John Stultz
2016-02-18 5:59 ` [PATCH] proc: /proc/<pid>/timerslack_ns permissions fixes John Stultz
2016-02-18 17:52 ` Kees Cook
2016-07-13 23:47 ` John Stultz [this message]
2016-07-14 3:39 ` [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface Kees Cook
2016-07-14 5:29 ` Arjan van de Ven
2016-07-14 12:48 ` Serge E. Hallyn
2016-07-14 13:42 ` Arjan van de Ven
2016-07-14 16:01 ` John Stultz
2016-07-14 16:09 ` John Stultz
2016-07-14 17:45 ` Kees Cook
2016-07-14 17:48 ` Arjan van de Ven
2016-07-14 17:49 ` Serge E. Hallyn
2016-07-14 17:56 ` Kees Cook
2016-07-14 20:21 ` Serge E. Hallyn
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