linux-kernel - Re: [RFC 2/2] initramfs with digital signature protection

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Date:	Wed, 10 Apr 2013 17:05:22 -0400
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Josh Boyer <jwboyer@...il.com>,
	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/2] initramfs with digital signature protection

On Wed, 2013-04-10 at 15:42 -0400, Vivek Goyal wrote:
> On Tue, Apr 09, 2013 at 11:07:10PM -0400, Mimi Zohar wrote:
> 
> [..]
> > The module keyring is a special case.  Loading these keys from the
> > kernel and, presumably, locking the keyring is probably fine.  In the
> > case of IMA, however, files will be signed by any number of package
> > owners.  If the _ima keyring is locked by the kernel, how would you add
> > these other keys?
> 
> Who are package owners here. IOW, in typical IMA setup, where are the keys
> and when are these keys loaded in ima keyring?

Suppose I install third party packages not signed by the distro, but by
the package owner (eg. google, rpmfusion, ...).  Not only does the
package signature need to be verified on installation, but the files
need to be installed with signatures.  For IMA to enforce file
integrity, the package owner's public key needs to be added to the _ima
keyring.

> If we trust root and keys can be loaded any time later, then signed
> initramfs will not solve the problem either.

Locking the keyring in the kernel will limit the set of permitted keys
to only those specified in UEFI db or builtin.  Locking the keyring in
the "early" initramfs, will allow the system owner, whose key is in the
UEFI db, to specify additional keys, such as those for third party
packages.  Not all public keys belong in the UEFI db.

Mimi

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