linux-kernel - Re: [PATCH v3 2/2] modules:capabilities: add a per-task modules autoload restriction

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Date:   Fri, 5 May 2017 09:18:46 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Djalal Harouni <tixxdz@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Dongsu Park <dpark@...teo.net>,
        Casey Schaufler <casey@...aufler-ca.com>,
        James Morris <james.l.morris@...cle.com>,
        Paul Moore <paul@...l-moore.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>, Jessica Yu <jeyu@...hat.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        belakhdar abdeldjalil <zendyani@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v3 2/2] modules:capabilities: add a per-task modules
 autoload restriction

On Thu, May 4, 2017 at 6:07 AM, Djalal Harouni <tixxdz@...il.com> wrote:
> On Sat, Apr 22, 2017 at 2:17 PM, Djalal Harouni <tixxdz@...il.com> wrote:
>> On Sat, Apr 22, 2017 at 1:28 AM, Andy Lutomirski <luto@...capital.net> wrote:
> [...]
>>>
>>> My point is that all of these need some way to handle configuration
>>> and inheritance, and I don't think that a bunch of per-task prctls is
>>> the right way.  As just an example, saying that interactive users can
>>> autoload modules but other users can't, or that certain systemd
>>> services can, etc, might be nice.  Linus already complained that he
>>> (i.e. user "torvalds" or whatever) should be able to profile the
>>> kernel but that other uids should not be able to.
>>
>> Neat, maybe this could already be achieved with this interface and
>> systemd-logind,  "ModulesAutoloadUsers=andy" in logind.conf where
>> "andy" is the only logged-in user able to trigger and autoload kernel
>> modules. However maybe we should not restrict too much other bits or
>> functionality of the other users, please let me will follow up later
>> on it.
>>
>>> I personally like my implicit_rights idea, and it might be interesting
>>> to prototype it.
>>
>
> Andy following on the idea of per user settings, I'm curious did you
> manage to make some advance on how to store the user settings ? the
> user database format is old and not extensible, there was cgmanager or
> other libcgroup but for resources, and no simple thing for such
> restrictions example: "RestrictLinuxModules=user" that will prevent
> such users from making/loading extra Linux features/modules that are
> not already available...
>

I figured that user code would figure it out somehow.  Text config file?

There is another odd way it could be configured: just leave the inodes
around in /dev/rights with appropriate permissions.  Some startup
script could re-instantiate them with the same permissions (via a
syscall that does that atomically).