linux-kernel - Re: [RFC PATCH 12/12] IMA: Use the the system trusted keyrings instead of .ima

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Message-ID: <20160308163758.GA4934@localhost>
Date:	Tue, 8 Mar 2016 18:37:58 +0200
From:	Petko Manolov <petkan@...-labs.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 12/12] IMA: Use the the system trusted keyrings
 instead of .ima_mok [ver #2]

On 16-03-08 16:07:00, David Howells wrote:
> Petko Manolov <petkan@...-labs.com> wrote:
> 
> > > How about I change it to a choice-type item, with the following options:
> > > 
> > >  (1) No addition.
> > > 
> > >  (2) Addition restricted by built-in keyring.
> > > 
> > >  (3) Addition restricted by secondary keyring + built-in keyring.
> > > 
> > > where the second and third options then depend on the appropriate keyrings 
> > > being enabled.
> > 
> > I would suggest leaving (1) and (3).  Since secondary keyring only accepts
> > keys signed by certificate in the system keyring I think (2) is redundant.
> > It adds extra complexity (Kconfig is vague enough already) while it doesn't
> > increase the overall security by much.
> 
> If I remove option (2), that would mean that if you want to allow keys to be 
> added to .ima if they're signed by the built-in keyring, then you also allow 
> keys to be added to .ima if they're signed by the secondary keyring if 
> enabled.

Exactly.  The primary difference between the built-in and secondary keyring is 
that the latter is R/W.  Chances are the user want either no addition or need 
dynamic key add/remove.

I don't have strong opinions against (2).  This is more of a discussion whether 
we should sacrifice in favor of simplicity or flexibility.

> Remember - these keyrings aren't necessarily restricted to IMA.

I am well aware of that.  At some point (perhaps not now) i'd like to discuss 
allowing kernel module loading based on keys in the secondary keyring.  It is a 
niche feature for those machines that have uptime measured in years.  I 
certainly don't expect it to be something the regular desktop or embedded users 
need.

Another issue that we left unresolved is the system-wide blacklist keyring.  It 
is at the same hierarchy level as the secondary keyring and serves a similar 
purpose although in opposite direction.

		Petko