linux-kernel - Re: [PATCH v5 15/16] ima: Move dentries into ima

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Date:   Fri, 10 Dec 2021 07:40:41 -0500
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>,
        Christian Brauner <christian.brauner@...ntu.com>
Cc:     Stefan Berger <stefanb@...ux.ibm.com>,
        linux-integrity@...r.kernel.org, serge@...lyn.com,
        containers@...ts.linux.dev, dmitry.kasatkin@...il.com,
        ebiederm@...ssion.com, krzysztof.struczynski@...wei.com,
        roberto.sassu@...wei.com, mpeters@...hat.com, lhinds@...hat.com,
        lsturman@...hat.com, puiterwi@...hat.com, jamjoom@...ibm.com,
        linux-kernel@...r.kernel.org, paul@...l-moore.com, rgb@...hat.com,
        linux-security-module@...r.kernel.org, jmorris@...ei.org
Subject: Re: [PATCH v5 15/16] ima: Move dentries into ima_namespace

On Fri, 2021-12-10 at 07:09 -0500, Mimi Zohar wrote:
> On Fri, 2021-12-10 at 12:49 +0100, Christian Brauner wrote:
> > > There's still the problem that if you write the policy, making
> > > the file disappear then unmount and remount securityfs it will
> > > come back.  My guess for fixing this is that we only stash the
> > > policy file reference, create it if NULL but then set the pointer
> > > to PTR_ERR(-EINVAL) or something and refuse to create it for that
> > > value.
> > 
> > Some sort of indicator that gets stashed in struct ima_ns that the
> > file does not get recreated on consecutive mounts. That shouldn't
> > be hard to fix.

Yes, Stefan said he was doing that.

> The policy file disappearing is for backwards compatibility, prior to
> being able to extend the custom policy.  For embedded usecases,
> allowing the policy to be written exactly once might makes sense.  Do
> we really want/need to continue to support removing the policy in
> namespaces?

The embedded world tends also to be a big consumer of namespaces, so if
this semantic is for them, likely it should remain in the namespaced
IMA.

But how necessary is the semantic?  If we got rid of it from the whole
of IMA, what would break? If we can't think of anything it could likely
be removed from both namespaced and non-namespaced IMA.

James