linux-kernel - Re: [RFC PATCH 11/12] certs: Add a secondary system keyring that can be added to dynamically [ver #2]

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Date:	Tue, 08 Mar 2016 15:32:14 +0000
From:	David Howells <dhowells@...hat.com>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:	dhowells@...hat.com, linux-security-module@...r.kernel.org,
	keyrings@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 11/12] certs: Add a secondary system keyring that can be added to dynamically [ver #2]

Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:

> > The problem boils down to a difficulty in concocting a name that describes a
> > complex situation that may change depending on the configuration.  I can make
> > it "restrict_link_by_any_system_trusted" if you'd prefer.
> > 
> > That's why I want "system trusted keyrings" to refer to the builtin and the
> > secondary - *and* an extra UEFI keyring if we grow one of those.  It's a
> > collection of related keyrings.
> 
> Sigh, this is the same discussion we've had for years.

No, it isn't.

> The UEFI keys should not be trusted to validate the certificates being added
> to the IMA keyring.

A machine-security (e.g. UEFI) keyring will conceivably live in
certs/system_keyring.c and only be enabled if CONFIG_SYSTEM_TRUSTED_KEYRINGS=y
and, say, CONFIG_MACHINE_TRUSTED_KEYRING=y.  I didn't say that IMA necessarily
has to use it.

What we need to do is define a set of functions allow IMA to get the
restrictions it wants, depending on configuration.  In the code I currently
have, I think we have those:

	restrict_link_reject
	restrict_link_by_builtin_trusted
	restrict_link_by_system_trusted

If you really want, I can add a restrict_link_for_ima in there, but I'd rather
not if IMA can use whichever of the above three most suits it.  How about:

	restrict_link_reject
	restrict_link_by_builtin_trusted
	restrict_link_by_builtin_or_secondary_trusted

> Neither should the keys on the secondary keyring, unless specifically IMA
> Kconfig enabled, be used to validate the certificates being added to the IMA
> keyring.

Yes.

David