linux-kernel - Re: [RFC PATCH v3 00/13] Clavis LSM

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Message-ID: <b464675506fa8d7ccef737d3bcddd0ec26b9b2c3.camel@linux.ibm.com>
Date: Tue, 04 Mar 2025 21:20:15 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Paul Moore <paul@...l-moore.com>
Cc: Eric Snowberg <eric.snowberg@...cle.com>,
        David Howells
 <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        "open
 list:SECURITY SUBSYSTEM" <linux-security-module@...r.kernel.org>,
        David
 Woodhouse <dwmw2@...radead.org>,
        "herbert@...dor.apana.org.au"
 <herbert@...dor.apana.org.au>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Ard Biesheuvel <ardb@...nel.org>, James Morris <jmorris@...ei.org>,
        "Serge
 E. Hallyn" <serge@...lyn.com>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        Mickaël Salaün <mic@...ikod.net>,
        "casey@...aufler-ca.com" <casey@...aufler-ca.com>,
        Stefan Berger
 <stefanb@...ux.ibm.com>,
        "ebiggers@...nel.org" <ebiggers@...nel.org>,
        Randy
 Dunlap <rdunlap@...radead.org>,
        open list <linux-kernel@...r.kernel.org>,
        "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>
Subject: Re: [RFC PATCH v3 00/13] Clavis LSM

On Tue, 2025-03-04 at 21:09 -0500, Paul Moore wrote:
> On Tue, Mar 4, 2025 at 8:50 PM Mimi Zohar <zohar@...ux.ibm.com> wrote:
> > On Tue, 2025-03-04 at 19:19 -0500, Paul Moore wrote:
> > > On Tue, Mar 4, 2025 at 7:54 AM Mimi Zohar <zohar@...ux.ibm.com> wrote:
> > > > On Mon, 2025-03-03 at 17:38 -0500, Paul Moore wrote:
> > > > > On Fri, Feb 28, 2025 at 12:19 PM Mimi Zohar <zohar@...ux.ibm.com> wrote:
> > > > > > On Fri, 2025-02-28 at 11:14 -0500, Paul Moore wrote:
> > > > > > > On Fri, Feb 28, 2025 at 9:09 AM Mimi Zohar <zohar@...ux.ibm.com> wrote:
> > > > > > > > On Thu, 2025-02-27 at 17:22 -0500, Paul Moore wrote:
> > > > > 
> > > > > ...
> > > > > 
> > > > > > Ok, let's go through different scenarios to see if it would scale.
> > > > > > 
> > > > > > Scenario 1: Mostly distro signed userspace applications, minimum number of
> > > > > > developer, customer, 3rd party applications.
> > > > > > 
> > > > > > Scenario 2: Multiple developer, customer, 3rd party applications, signed by the
> > > > > > same party.
> > > > > > 
> > > > > > Scenario 3: extreme case - every application signed by different party.
> > > > > > 
> > > > > > With the minimum case, there would probably be a default key or sets of
> > > > > > permissible keys.  In the extreme case, the number of keyrings would be
> > > > > > equivalent to the number of application/software packages.
> > > > > 
> > > > > Perhaps we're not understanding each other, but my understanding of
> > > > > the above three scenarios is that they are all examples of signed
> > > > > applications where something (likely something in the kernel like IMA)
> > > > > verifies the signature on the application.  While there are going to
> > > > > be differing numbers of keys in each of the three scenarios, I believe
> > > > > they would all be on/linked-to the same usage oriented keyring as they
> > > > > all share the same usage: application signatures.
> > > > 
> > > > Yes they're all verifying file signatures, but the software packages are from
> > > > different sources (e.g. distro, chrome), signed by different keys.
> > > 
> > > Yep.
> > > 
> > > > Only a
> > > > particular key should be used to verify the file signatures for a particular
> > > > application.
> > > 
> > > That's definitely one access control policy, but I can also envision a
> > > scenario where I have just one keyring for application signatures with
> > > multiple keys from multiple vendors.
> > 
> > Having a single keyring with keys from multiple software vendors is the status
> > quo.
> 
> A single keyring with keys from multiple vendors does happen today
> yes, but there is no separation based on how those keys are used, e.g.
> separate application signature and kernel module signature keyrings.

As soon as you add multiple vendors keys on the kernel module signature keyring,
you'll need finer grained access control.

Mimi