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From: Paul Moore <paul@paul-moore.com>
Date: Wed, 17 Aug 2016 17:21:33 -0400
Message-ID: <CAHC9VhR8FUsPjt8KgW8Ub9Z5E4yXGesJ9314Z5hjH_QtR3kORw@mail.gmail.com>
Subject: Re: [PATCH 2/2 v4] proc: Add LSM hook checks to /proc/<tid>/timerslack_ns
To: John Stultz <john.stultz@linaro.org>
Cc: lkml <linux-kernel@vger.kernel.org>, Kees Cook <keescook@chromium.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Oren Laadan <orenl@cellrox.com>, Ruchi Kandoi <kandoiruchi@google.com>,
        Rom Lemarchand <romlem@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>,
        James Morris <jmorris@namei.org>,
        Android Kernel Team <kernel-team@android.com>,
        linux-security-module@vger.kernel.org, selinux@tycho.nsa.gov
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On Thu, Jul 21, 2016 at 4:24 PM, John Stultz <john.stultz@linaro.org> wrote:
> As requested, this patch checks the existing LSM hooks
> task_getscheduler/task_setscheduler when reading or modifying
> the task's timerslack value.
>
> Previous versions added new get/settimerslack LSM hooks, but
> since they checked the same PROCESS__SET/GETSCHED values as
> existing hooks, it was suggested we just use the existing ones.
>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: "Serge E. Hallyn" <serge@hallyn.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> CC: Arjan van de Ven <arjan@linux.intel.com>
> Cc: Oren Laadan <orenl@cellrox.com>
> Cc: Ruchi Kandoi <kandoiruchi@google.com>
> Cc: Rom Lemarchand <romlem@android.com>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Colin Cross <ccross@android.com>
> Cc: Nick Kralevich <nnk@google.com>
> Cc: Dmitry Shmidt <dimitrysh@google.com>
> Cc: Elliott Hughes <enh@google.com>
> Cc: James Morris <jmorris@namei.org>
> Cc: Android Kernel Team <kernel-team@android.com>
> Cc: linux-security-module@vger.kernel.org
> Cc: selinux@tycho.nsa.gov
> Signed-off-by: John Stultz <john.stultz@linaro.org>
> ---
> v2:
>  * Initial swing at adding settimerslack LSM hook
> v3:
>  * Fix current/p switchup bug noted by NickK
>  * Add gettimerslack hook suggested by NickK
> v4:
>  * Dropped adding get/settimerslack LSM hooks, and
>    just reuse the get/setscheduler ones.
>
>  fs/proc/base.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)

For some reason I'm having a hard time finding patch 1/2 in the
patchset, but this patch looks reasonable to me.  We already have some
LSM checking via the ptrace_may_access() call, but this adds some
additional granularity which could be a good thing.

Acked-by: Paul Moore <paul@paul-moore.com>

> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index c94abae..02f8389 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2286,6 +2286,12 @@ static ssize_t timerslack_ns_write(struct file *file, const char __user *buf,
>                 goto out;
>         }
>
> +       err = security_task_setscheduler(p);
> +       if (err) {
> +               count = err;
> +               goto out;
> +       }
> +
>         task_lock(p);
>         if (slack_ns == 0)
>                 p->timer_slack_ns = p->default_timer_slack_ns;
> @@ -2314,6 +2320,10 @@ static int timerslack_ns_show(struct seq_file *m, void *v)
>                 goto out;
>         }
>
> +       err = security_task_getscheduler(p);
> +       if (err)
> +               goto out;
> +
>         task_lock(p);
>         seq_printf(m, "%llu\n", p->timer_slack_ns);
>         task_unlock(p);
> --
> 1.9.1
>
> --
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-- 
paul moore
www.paul-moore.com