linux-kernel - Re: [PATCH 10/8] modsign: Allow password to be specified for signing key

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Date:	Tue, 19 May 2015 19:34:27 +0300
From:	Petko Manolov <petkan@...-labs.com>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	dhowells@...hat.com, rusty@...tcorp.com.au, mmarek@...e.cz,
	mjg59@...f.ucam.org, keyrings@...ux-nfs.org,
	dmitry.kasatkin@...il.com, mcgrof@...e.com,
	linux-kernel@...r.kernel.org, seth.forshee@...onical.com,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH 10/8] modsign: Allow password to be specified for signing
 key

On 15-05-19 17:15:12, David Woodhouse wrote:
> On Tue, 2015-05-19 at 18:50 +0300, Petko Manolov wrote:
> > On 15-05-19 15:45:58, David Woodhouse wrote:
> > > We don't want this in the Kconfig since it might then get exposed in
> > > /proc/config.gz. So make it a parameter to Kbuild instead. This also
> > > means we don't have to jump through hoops to strip quotes from it, as
> > > we would if it was a config option.
> > 
> > If it were on a network-less, secure sign/build server i'd say it is OK.  
> > 
> > However, exposing your private key's password in an environment variable on a 
> > regular Linux box is a bit fishy.
> 
> I don't quite understand the objection.
> 
> If you want the modules to be signed with an external key of your
> choice, then for the duration of the 'make modules_sign' run (or 'make
> modules_install if CONFIG_MODULE_SIG_ALL=y) surely the password has to
> be available *somehow*? 
> 
> You are, of course, free to sign the modules by invoking sign-file
> directly. In which case you *still* need to provide it with the password
> for the key somehow, if there is one.
> 
> Mimi quite rightly pointed out that my original mechanism for this, a
> CONFIG_MODULE_SIG_KEY_PASSWORD option, was inadvertently exposing it
> more than was necessary.
> 
> As it is now, you *only* need it in the environment for the duration of
> the operations that actually *use* it.

As with everything there is bad and good side to your proposal.

bad:
  - password in environment variable _could_ be very dangerous;
  - someone is bound to misuse this feature sooner or later;

good:
  - the actual risk is mitigated as the key is very short-lived;
  - the feature is going to be used by a small number of people;
  - does not break automated builds, maybe;
  - there is an alternative for those who want more secure approach;

> Do you have a better suggestion?

*better* is a matter of prospective.  Security and convenience are at the wrong 
side of the spectrum relative to each other. :)

Don't get me wrong, your patch is perhaps the lesser evil.  I just wanted to 
bring up my concerns.


cheers,
Petko
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