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

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Message-ID: <CALCETrWNY9Ea=3dKksFJjizoH5eZbVOFWFnWoJrCRwP0R1QWHg@mail.gmail.com>
Date:   Mon, 13 Feb 2017 11:01:44 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Kees Cook <keescook@...omium.org>
Cc:     Djalal Harouni <tixxdz@...il.com>,
        Linux API <linux-api@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Lafcadio Wluiki <wluikil@...il.com>
Subject: Re: [PATCH v4 2/2] procfs/tasks: add a simple per-task procfs
 hidepid= field

On Fri, Feb 10, 2017 at 3:44 PM, Kees Cook <keescook@...omium.org> wrote:
> On Wed, Jan 18, 2017 at 3:35 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> On Wed, Jan 18, 2017 at 2:50 PM, Djalal Harouni <tixxdz@...il.com> 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.

--Andy