linux-kernel - Re: [PATCH 3/4] capability: Create a new capability CAP

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Date:	Wed, 20 Mar 2013 14:50:59 +0000
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	James Morris <jmorris@...ei.org>,
	Casey Schaufler <casey@...aufler-ca.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-security-module@...r.kernel.org" 
	<linux-security-module@...r.kernel.org>,
	"zohar@...ux.vnet.ibm.com" <zohar@...ux.vnet.ibm.com>,
	"dmitry.kasatkin@...el.com" <dmitry.kasatkin@...el.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"ebiederm@...ssion.com" <ebiederm@...ssion.com>,
	"serge@...lyn.com" <serge@...lyn.com>,
	"morgan@...nel.org" <morgan@...nel.org>
Subject: Re: [PATCH 3/4] capability: Create a new capability CAP_SIGNED

On Wed, 2013-03-20 at 10:41 -0400, Vivek Goyal wrote:

> I am not sure why CAP_COMPROMISE_KERNEL(CAP_MODIFY_KERNEL) is any
> different. When secureboot is enabled, kernel will take away that
> capability from all the processes. So kernel became a decision maker
> too whether processes have CAP_COMPROMISE_KERNEL or not based on
> certain other factors like secureboot is enabled or not.

No, that's a limited case. Outside of that, it's an access control
capability in exactly the same way as CAP_SYS_RAWIO is. The easiest way
to think of this is probably whether it ever makes sense for an
arbitrary binary run as root to possess that capability. For
CAP_COMPROMISE_KERNEL the answer is yes - for CAP_SIGNED, the answer is
no.

Just have a flag somewhere in the process structure that indicates
whether it was signed. There's no need to use capabilities here.
-- 
Matthew Garrett | mjg59@...f.ucam.org