linux-kernel - Re: [RFC 1/1] ima: digital signature verification using asymmetric keys

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Message-ID: <1359489673.816.25.camel@falcor1.watson.ibm.com>
Date:	Tue, 29 Jan 2013 15:01:13 -0500
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>,
	dhowells@...hat.com, jmorris@...ei.org,
	linux-security-module@...r.kernel.org,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/1] ima: digital signature verification using asymmetric
 keys

On Tue, 2013-01-29 at 13:20 -0500, Vivek Goyal wrote:
> On Mon, Jan 28, 2013 at 08:48:55PM -0500, Mimi Zohar wrote:
> 
> [..]
> > > Hi Mimi,
> > > 
> > > By policy you mean ima rules here? So I can either enable default rules
> > > (tcb default rules for appraisal and measurement) by using kernel command
> > > line options or dynamically configure my own rules using /sysfs interface?
> > > 
> > > If yes, AFAIK, existing inputtable policies do not allow this selective
> > > mode where we do appraisal only on signed executable. That means I shall
> > > have to extend the way policies can be specified so that one specify
> > > that appraise only signed files?
> > 
> > We've just added the ability of defining the method for appraising a
> > file and defining rules in terms of the filesystem UUID.  Extending the
> > IMA policy shouldn't be a problem, but I'm not sure how you would go
> > about adding support for only appraising files with digital signatures.
> 
> Hi Mimi,
> 
> Can we add another field to ima_rule_entry, say .enforcement to control
> the behavior of .action. Possible values of .enforcement could be, say.
> 
> ALL
> SIGNED_ONLY
> 
> ALL will be default. And with .action= MEASURE, one could possibly use
> .enforcement=SIGNED_ONLY.

Other than the .action being '.action=APPRAISE', not 'MEASURE',
something like what you're suggesting, could work.  How about extending
the new 'appraise_type=' option?   The appraise_type enforces a
particular type (eg. hash, signature) of verification. 

option: appraise_type:= [imasig[,signed_only]]
eg. appraise_type=imasig,signed_only

thanks,

Mimi

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