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

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Message-ID: <d72550d9690d563e4c43220111b39d2d55ea10ff.camel@linux.ibm.com>
Date:   Fri, 10 Dec 2021 07:54:44 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     jejb@...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 07:40 -0500, James Bottomley wrote:
> 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.

Think of a simple device that loads a custom IMA policy, which never
changes once loaded.
> 
> 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.

The question isn't an issue of "breaking", but of leaking info.  If
this isn't a real concern, then the ability of removing the securityfs
isn't needed.

thanks,

Mimi