linux-kernel - Re: [PATCH] X.509: Partially revert patch to add validation against IMA MOK keyring

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Date:	Wed, 06 Jan 2016 22:28:20 -0500
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	David Howells <dhowells@...hat.com>
Cc:	petkan@...-labs.com, jmorris@...ei.org,
	linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] X.509: Partially revert patch to add validation against
 IMA MOK keyring

On Wed, 2016-01-06 at 21:13 -0500, Mimi Zohar wrote:
> On Thu, 2016-01-07 at 00:34 +0000, David Howells wrote:
> > David Howells <dhowells@...hat.com> wrote:
> > 
> > > Partially revert commit 41c89b64d7184a780f12f2cccdabe65cb2408893:
> > > 
> > > 	Author: Petko Manolov <petkan@...-labs.com>
> > > 	Date:   Wed Dec 2 17:47:55 2015 +0200
> > > 	IMA: create machine owner and blacklist keyrings
> > > 
> > > The problem is that prep->trusted is a simple boolean and the additional
> > > x509_validate_trust() call doesn't therefore distinguish levels of
> > > trustedness, but is just OR'd with the result of validation against the
> > > system trusted keyring.
> > > 
> > > However, setting the trusted flag means that this key may be added to *any*
> > > trusted-only keyring - including the system trusted keyring.
> 
> Hm, I'm not able to add a key to the system keyring that is signed by a
> key on either the system or the IMA MOK keyrings.  The system keyring
> seems to be "locked".  A key that is signed by either a key on the
> system or the IMA MOK keyring can be added to the IMA keyring.
> 
> keyctl show %keyring:.system_keyring
> Keyring
>  973688077 ---lswrv      0     0  keyring: .system_keyring
>     
> evmctl import m1-cert-signed.der 973688077
> add_key failed
> errno: Permission denied (13)

The "KEY_USR_WRITE" permission is required in order to add keys to a
keyring.  This permission is specified for the IMA keyring, but not for
the system keyring, which explains why I could add a key to the IMA
keyring, but not the system keyring.

       system_trusted_keyring =
                keyring_alloc(".system_keyring",
                              KUIDT_INIT(0), KGIDT_INIT(0),
current_cred(),
                              ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
                              KEY_USR_VIEW | KEY_USR_READ |
KEY_USR_SEARCH),
                              KEY_ALLOC_NOT_IN_QUOTA, NULL);

       keyring[id] = keyring_alloc(keyring_name[id], KUIDT_INIT(0),
                                    KGIDT_INIT(0), cred,
                                    ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
                                     KEY_USR_VIEW | KEY_USR_READ |
                                     KEY_USR_WRITE | KEY_USR_SEARCH),
                                    KEY_ALLOC_NOT_IN_QUOTA, NULL);

The only keys added to the system keyring should be those listed in the
Kconfig SYSTEM_TRUSTED_KEYS specified file.
  
Mimi

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