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

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Message-ID: <20110228095133.GA4351@albatros>
Date:	Mon, 28 Feb 2011 12:51:33 +0300
From:	Vasiliy Kulikov <segoon@...nwall.com>
To:	Michael Tokarev <mjt@....msk.ru>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Michał Mirosław <mirqus@...il.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	David Miller <davem@...emloft.net>, 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 Mon, Feb 28, 2011 at 12:29 +0300, Michael Tokarev wrote:
> 27.02.2011 23:22, Arnd Bergmann wrote:
> > The backwards compatibility should mostly be for systems that today don't
> > use split capabilities, right?
> > 
> > The fallback could therefore rely on CAP_SYS_MODULE as well:
> > 
> > 	if (request_module("netdev-%s", name)) {
> > 		if (capable(CAP_SYS_MODULE))
> > 			request_module("%s", name);
> > 	}
> > 
> > Not 100% solution, but should solve the capability escalation nicely without
> > causing much pain.
> 
> To me this looks like the best solution so far - trivial and
> compatible.

Agreed, it's looks good.  But before the request_module() there is a check
for capabile(CAP_NET_ADMIN), IMO it's better to request either
CAP_NET_ADMIN or CAP_SYS_MODULE, not both of them.

	if (!dev) {
        if (capable(CAP_NET_ADMIN))
            request_module("netdev-%s", name))
        if (capable(CAP_SYS_MODULE) {
            if (!request_module("%s", name))
                WARN_ONE(1, "Loading kernel module for a network device"
" with CAP_SYS_MODULE (deprecated).  Use CAP_NET_ADMIN and alias"
" netdev-%s instead\n", name);
        }
    }

The only drawback is distributions/setups that already use
CAP_SYS_MODULE'less network scripts.

David, are you OK with this way?


Thanks,

-- 
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
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