linux-kernel - Re: [PATCH 00/12] One more attempt at useful kernel lockdown

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Date:	Mon, 9 Sep 2013 23:02:05 +0000
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	David Lang <david@...g.hm>
CC:	"Valdis.Kletnieks@...edu" <Valdis.Kletnieks@...edu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"keescook@...omium.org" <keescook@...omium.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"jmorris@...ei.org" <jmorris@...ei.org>,
	"linux-security-module@...r.kernel.org" 
	<linux-security-module@...r.kernel.org>
Subject: Re: [PATCH 00/12] One more attempt at useful kernel lockdown

On Mon, 2013-09-09 at 11:25 -0700, David Lang wrote:

> 1 lock down modules
> 2 lock down kexec

Having thought about this, the answer is no. It presents exactly the
same problem as capabilities do - the set can never be meaningfully
extended. If an application sets only the bits it knows about, and if a
new security-sensitive feature is added to the kernel, the feature will
be left enabled and the system will be insecure. Alternatively, if an
application sets all the bits regardless of whether it knows them or
not, it may enable a lockdown feature that it otherwise required.

The only way this is useful is if all the bits are semantically
equivalent, and in that case there's no point in having anything other
than a single bit. Users who want a more fine-grained interface should
use one of the existing mechanisms for doing so - leave the kernel open
and impose the security policy from userspace using either capabilities
or selinux.

-- 
Matthew Garrett <matthew.garrett@...ula.com>