linux-kernel - Re: [kernel-hardening] Re: [PATCH v3 1/2] modules:capabilities: automatic module loading restriction

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Date:   Thu, 20 Apr 2017 16:02:23 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     Djalal Harouni <tixxdz@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Serge E. Hallyn" <serge@...lyn.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>, Zendyani <zendyani@...il.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [kernel-hardening] Re: [PATCH v3 1/2] modules:capabilities:
 automatic module loading restriction

On Thu, 2017-04-20 at 14:44 +0200, Djalal Harouni wrote:
> > On Thu, Apr 20, 2017 at 4:22 AM, Ben Hutchings <ben@...adent.org.uk> wrote:
> > On Thu, 2017-04-20 at 00:20 +0200, Djalal Harouni wrote:
> > [...]
> > > +modules_autoload:
> > > +
> > > +A sysctl to control if modules auto-load feature is allowed or not.
> > > +This sysctl complements "modules_disabled" which is for all module
> > > +operations where this flag applies only to automatic module loading.
> > > +Automatic module loading happens when programs request a kernel feature
> > > +that is implemented by an unloaded module, the kernel automatically
> > > +runs the program pointed by "modprobe" sysctl in order to load the
> > > +corresponding module.
> > > +
> > > +When modules_autoload is set to (0), the default, there are no
> > > +restrictions.
> > > +
> > > +When modules_autoload is set to (1), processes must have CAP_SYS_MODULE
> > > +to be able to trigger a module auto-load operation, or CAP_NET_ADMIN
> > > +for modules with a 'netdev-%s' alias.
> > > +
> > > +When modules_autoload is set to (2), automatic module loading is
> > > +disabled for all. Once set, this value can not be changed.
> > 
> > I would expect a parameter 'modules_autoload' to be a boolean, so this
> > behaviour would be surprising.
> > 
> > What is the point of mode 2?  Why would someone want to set
> > modules_disabled=0 and modules_autoload=2?
> 
> modules_disabled is too restrictive and once set it can't be changed,
> maybe that's why not all users use it.
> 
> With modules_disabled=0 and modules_autoload=2
[...]

Hmm, OK.  How about naming this modules_autoload_mode, then, so that
it's obviously not a boolean?

Ben.

-- 
Ben Hutchings
It is easier to change the specification to fit the program than vice
versa.


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