From: Andrew Morton <akpm@linux-foundation.org>
To: John Stultz <john.stultz@linaro.org>
Cc: Kees Cook <keescook@chromium.org>,
Thomas Gleixner <tglx@linutronix.de>,
Arjan van de Ven <arjan@linux.intel.com>,
lkml <linux-kernel@vger.kernel.org>,
Oren Laadan <orenl@cellrox.com>,
Ruchi Kandoi <kandoiruchi@google.com>,
Rom Lemarchand <romlem@android.com>,
Android Kernel Team <kernel-team@android.com>
Subject: Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface
Date: Wed, 17 Feb 2016 14:53:37 -0800 [thread overview]
Message-ID: <20160217145337.9f640ce0.akpm@linux-foundation.org> (raw)
In-Reply-To: <CALAqxLVHBjPrfn8fK5W2ER7gkfMB2QoTthPAie9iQYaB-CdYfg@mail.gmail.com>
On Wed, 17 Feb 2016 14:29:29 -0800 John Stultz <john.stultz@linaro.org> wrote:
> On Wed, Feb 17, 2016 at 12:18 PM, Andrew Morton
> <akpm@linux-foundation.org> wrote:
> > On Wed, 17 Feb 2016 12:09:08 -0800 Kees Cook <keescook@chromium.org> wrote:
> >> On Wed, Feb 17, 2016 at 11:35 AM, Andrew Morton
> >> > The procfs file's permissions are 0644, yes? So a process's
> >> > timer_slack is world-readable? hm.
> >>
> >> This should be 600, IMO.
> >
> > Sounds safer.
>
> So I've gone ahead and addressed this and the other feedback you had.
> But this bit made me realize that I may have missed a key aspect to
> the interface that Android needs.
>
> In particular, the whole point here is to allow a controlling task to
> modify other tasks' timerslack to limit background tasks' power usage
> (and to modify them back to normal when the background tasks become
> foreground tasks). Note that on android different tasks run as
> different users.
>
> Currently, the controlling process has minimally elevated privileges
> (CAP_SYS_NICE). The initial review suggested those privileges should
> be higher (PTRACE_MODE_ATTACH), which I've implemented. However, I'm
> realizing that by moving to the proc interface, the filesystem
> permissions here put yet another barrier in the way.
>
> While the 600 permissions makes initial sense, it does limit these
> controlling tasks with extra privileges (though not root) from
> modifying the timerslack, since they cannot open the file to begin
> with.
>
> So.... Does world writable (plus the PTRACE_MODE_ATTACH_FSCREDS check)
> make more sense here? Or is there a better way for a system to tweak
> the default permissions for procfs entries? (And if so, does that
> render the PTRACE_MODE_ATTACH... check unnecessary?).
I can't immediately think of a problem with it. Could we check
PTRACE_MODE_ATTACH_FSCREDS in open() to prevent bad guys from reading
our timerslack?
next prev parent reply other threads:[~2016-02-17 22:47 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 [this message]
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 ` [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface John Stultz
2016-07-14 3:39 ` 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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