Subject: Re: [PATCH] don't allow CAP_NET_ADMIN to load non-netdev kernel
 modules
From: Ben Hutchings <bhutchings@solarflare.com>
To: David Miller <davem@davemloft.net>
Cc: segoon@openwall.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        kuznet@ms2.inr.ac.ru, pekkas@netcore.fi, jmorris@namei.org,
        yoshfuji@linux-ipv6.org, kaber@trash.net, eric.dumazet@gmail.com,
        therbert@google.com, xiaosuo@gmail.com, jesse@nicira.com,
        kees.cook@canonical.com, eugene@redhat.com, dan.j.rosenberg@gmail.com,
        akpm@linux-foundation.org
In-Reply-To: <20110225.114351.28809001.davem@davemloft.net>
References: <1298660879.2554.23.camel@bwh-desktop>
	 <20110225.111606.115927805.davem@davemloft.net>
	 <1298662216.2554.33.camel@bwh-desktop>
	 <20110225.114351.28809001.davem@davemloft.net>
Content-Type: text/plain; charset="UTF-8"
Organization: Solarflare Communications
Date: Fri, 25 Feb 2011 19:53:05 +0000
Message-ID: <1298663585.2554.39.camel@bwh-desktop>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2017
Lines: 50

On Fri, 2011-02-25 at 11:43 -0800, David Miller wrote:
> From: Ben Hutchings <bhutchings@solarflare.com>
> Date: Fri, 25 Feb 2011 19:30:16 +0000
> 
> > On Fri, 2011-02-25 at 11:16 -0800, David Miller wrote:
> >> From: Ben Hutchings <bhutchings@solarflare.com>
> >> Date: Fri, 25 Feb 2011 19:07:59 +0000
> >> 
> >> > You realise that module loading doesn't actually run in the context of
> >> > request_module(), right?
> >> 
> >> Why is that a barrier?  We could simply pass a capability mask into
> >> request_module if necessary.
> >> 
> >> It's an implementation detail, and not a deterrant to my suggested
> >> scheme.
> > 
> > It's not an implementation detail.  modprobe currently runs with full
> > capabilities; your proposal requires its capabilities to be limited to
> > those of the capabilities of the process that triggered the
> > request_module() (plus, presumably, CAP_SYS_MODULE).
> 
> The idea was that the kernel will be the entity that will inspect the
> elf sections and validate the capability bits, not the userspace
> module loader.

Yes, I understand that.

> Surely we if we can pass an arbitrary string out to the loading
> process as part of the module loading context, we can pass along
> capability bits as well.

If you want insert_module() to be able to deny loading some modules
based on the capabilities of the process calling request_module() then
you either have to *reduce* the capabilities given to modprobe or create
some extra process state, separate from the usual capability state,
specifically for this purpose.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/