Re: [PATCH v4 2/2] procfs/tasks: add a simple per-task procfs hidepid= field

From: Andy Lutomirski
Date: Mon Feb 13 2017 - 14:02:13 EST

On Fri, Feb 10, 2017 at 3:44 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Wed, Jan 18, 2017 at 3:35 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>> On Wed, Jan 18, 2017 at 2:50 PM, Djalal Harouni <tixxdz@xxxxxxxxx> wrote:
>>> Andy I don't follow here, no_new_privs is never cleared right ? I
>>> can't see the corresponding clear bit code for it.
>> I believe that unsharing userns clears no_new_privs.
> Seriously? That's kind of ... weird. I mean, I guess you're
> priv-confined in a way, but that seems fragile.

I appear to have made this up. Either I genuinely pulled it out of
thin air or it was discussed and not done.

$ setpriv --nnp unshare -Ur cat /proc/self/status |grep NoNewPrivs
NoNewPrivs: 1

If it were to be done, it ought to be quite safe except for possible LSM issues.