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Message-ID: <CALCETrV0zb-Sm=L1CG6z9uQc1W+Wh2KTpAx5vUm8pcn+-qmsFg@mail.gmail.com>
Date: Wed, 20 May 2015 09:41:21 -0700
From: Andy Lutomirski <luto@...capital.net>
To: Andy Lutomirski <luto@...capital.net>,
David Howells <dhowells@...hat.com>,
Andy Lutomirski <luto@...nel.org>,
Rusty Russell <rusty@...tcorp.com.au>,
Michal Marek <mmarek@...e.cz>,
Matthew Garrett <mjg59@...f.ucam.org>, keyrings@...ux-nfs.org,
Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
Luis Rodriguez <mcgrof@...e.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Seth Forshee <seth.forshee@...onical.com>,
LSM List <linux-security-module@...r.kernel.org>,
David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 0/8] MODSIGN: Use PKCS#7 for module signatures [ver #4]
On Wed, May 20, 2015 at 9:21 AM, Petko Manolov <petkan@...-labs.com> wrote:
> On 15-05-20 08:56:21, Andy Lutomirski wrote:
>>
>> Would it make more sense to permit X.509 chains to be loaded into the keyring
>> instead if we actually need that feature? IOW, let userspace (or early
>> initramfs stuff) extend our keyring trust to intermediate certs that validly
>> chain to already-trusted things? I think that a reasonable design goal would
>> be that everything overcomplicated that's involved should be optional, and
>> moving toward embedding PKCS#7 signatures in the modules themselves does the
>> other direction?
>
> This is similar to what i am doing right now - create CA hierarchy so we can
> have something like:
>
> +-> KeyB
> |
> RootCA ---> CertA ---> CertB ---> CertC ---> KeyC
> |
> +-> CertA' ---> KeyA"
>
> The RootCA may be the one whose private key was used to sign the modules and all
> downstream certificates are either directly signed by it or one of the others.
> Not all of the infrastructure is in the mainline kernel, but this can easily be
> rectified.
Right. I guess that I can imagine some uses for this, but I don't see
why those intermediate certs would be embedded with the signatures
being verified as opposed to being loaded beforehand.
>
> Now, as Mimi pointed out this scheme is flawed and should be used with care if
> at all. Revoking certificates is always a PITA. Being valid for one year only
> adds to the fun.
>
Valid for only one year is worse than that. We might be verifying the
signature on our clock driver :) I think that, at best, we could
reject certificates that expired before the running kernel was built.
>
> Petko
--
Andy Lutomirski
AMA Capital Management, LLC
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