linux-kernel - Re: [RFC][PATCH 1/2 v2] proc: Relax /proc/<tid>/timerslack

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Date:	Fri, 15 Jul 2016 13:03:14 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Nick Kralevich <nnk@...gle.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Kees Cook <keescook@...omium.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Oren Laadan <orenl@...lrox.com>,
	Ruchi Kandoi <kandoiruchi@...gle.com>,
	Rom Lemarchand <romlem@...roid.com>,
	Todd Kjos <tkjos@...gle.com>, Colin Cross <ccross@...roid.com>,
	Dmitry Shmidt <dimitrysh@...gle.com>,
	Elliott Hughes <enh@...gle.com>,
	Android Kernel Team <kernel-team@...roid.com>,
	LSM List <linux-security-module@...r.kernel.org>,
	SELinux <selinux@...ho.nsa.gov>
Subject: Re: [RFC][PATCH 1/2 v2] proc: Relax /proc/<tid>/timerslack_ns
 capability requirements

On Fri, Jul 15, 2016 at 12:55 PM, Nick Kralevich <nnk@...gle.com> wrote:
> On Fri, Jul 15, 2016 at 10:24 AM, John Stultz <john.stultz@...aro.org> wrote:
>> +       if (!capable(CAP_SYS_NICE))
>> +               return -EPERM;
>> +
>>         p = get_proc_task(inode);
>>         if (!p)
>>                 return -ESRCH;
>
> The capable(CAP_SYS_NICE) permission check should be moved to this
> point, since it doesn't make sense to return EPERM if the task
> structure doesn't exist.

Ok. Will move it.

>> @@ -2300,22 +2300,21 @@ static int timerslack_ns_show(struct seq_file *m, void *v)
>>  {
>>         struct inode *inode = m->private;
>>         struct task_struct *p;
>> -       int err =  0;
>> +
>> +       if (!capable(CAP_SYS_NICE))
>> +               return -EPERM;
>
> This should also have a similar LSM check for reads. For the SELinux
> implementation, this can map to the PROCESS__GETSCHED permission.

Ok. I'll wire that in as well.

Would adding both selinux_task_get and set methods in the same patch
be ok? Or would folks prefer they be split into two?

Thanks for the feedback!
-john