linux-kernel - Re: Migration to trusted keys: sealing user-provided key?

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Message-ID: <35960.1612199062@warthog.procyon.org.uk>
Date:   Mon, 01 Feb 2021 17:04:22 +0000
From:   David Howells <dhowells@...hat.com>
To:     Jan =?ISO-8859-1?Q?L=FCbbe?= 
        <jlu@...gutronix.de>
Cc:     dhowells@...hat.com, Mimi Zohar <zohar@...ux.ibm.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Ahmad Fatoum <a.fatoum@...gutronix.de>,
        James Bottomley <jejb@...ux.ibm.com>, keyrings@...r.kernel.org,
        Sumit Garg <sumit.garg@...aro.org>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, kernel@...gutronix.de
Subject: Re: Migration to trusted keys: sealing user-provided key?

Jan Lübbe <jlu@...gutronix.de> wrote:

> > > ... But at this point, you can still do 'keyctl read' on that key, exposing
> > > the key material to user space.
> > 
> > I wonder if it would help to provide a keyctl function to mark a key as being
> > permanently unreadable - so that it overrides the READ permission bit.
> > 
> > Alternatively, you can disable READ and SETATTR permission - but that then
> > prevents you from removing other perms if you want to :-/
> 
> That would mean using user type keys, right? Then we'd still have the core
> problem how a master key can be protected against simply reading it from
> flash/disk, as it would be unencrypted in this scenario.

It would apply to any type of key or keyring on which it was set.  It would
cause keyctl_read() on a flagged key to return EPERM.

David