linux-kernel - Re: [PATCH] don't allow CAP_NET_ADMIN to load non-netdev kernel modules

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Date:	Fri, 25 Feb 2011 19:53:05 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	David Miller <davem@...emloft.net>
Cc:	segoon@...nwall.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, kuznet@....inr.ac.ru,
	pekkas@...core.fi, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net, eric.dumazet@...il.com, therbert@...gle.com,
	xiaosuo@...il.com, jesse@...ira.com, kees.cook@...onical.com,
	eugene@...hat.com, dan.j.rosenberg@...il.com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] don't allow CAP_NET_ADMIN to load non-netdev kernel
 modules

On Fri, 2011-02-25 at 11:43 -0800, David Miller wrote:
> From: Ben Hutchings <bhutchings@...arflare.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@...arflare.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.

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