Message-ID: <d72550d9690d563e4c43220111b39d2d55ea10ff.camel@linux.ibm.com>
Subject: Re: [PATCH v5 15/16] ima: Move dentries into ima_namespace
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     jejb@linux.ibm.com,
        Christian Brauner <christian.brauner@ubuntu.com>
Cc:     Stefan Berger <stefanb@linux.ibm.com>,
        linux-integrity@vger.kernel.org, serge@hallyn.com,
        containers@lists.linux.dev, dmitry.kasatkin@gmail.com,
        ebiederm@xmission.com, krzysztof.struczynski@huawei.com,
        roberto.sassu@huawei.com, mpeters@redhat.com, lhinds@redhat.com,
        lsturman@redhat.com, puiterwi@redhat.com, jamjoom@us.ibm.com,
        linux-kernel@vger.kernel.org, paul@paul-moore.com, rgb@redhat.com,
        linux-security-module@vger.kernel.org, jmorris@namei.org
Date:   Fri, 10 Dec 2021 07:54:44 -0500
In-Reply-To: <d321f676a5ba54ae1704f5e23f0b134e70dfea3f.camel@linux.ibm.com>
References: <20211208221818.1519628-1-stefanb@linux.ibm.com>
         <20211208221818.1519628-16-stefanb@linux.ibm.com>
         <20211209143428.ip6bwry5hqtee5vy@wittgenstein>
         <20211209143749.wk4agkynfqdzftbl@wittgenstein>
         <fb99af21f029b8072435e35731b919f4ec98f89d.camel@linux.ibm.com>
         <e2feaf2f6ac4bc82f328f94ca35d14cdc3ca79d1.camel@linux.ibm.com>
         <20211210114934.tacjnwryihrsx6ln@wittgenstein>
         <2587716d7d021c35e3b6ef22b6e30f44c2b3f98e.camel@linux.ibm.com>
         <d321f676a5ba54ae1704f5e23f0b134e70dfea3f.camel@linux.ibm.com>
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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