linux-kernel - Re: [PATCH v9 10/23] ima: Move IMA securityfs files into ima

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Message-ID: <714ef8a702e162fd9110f54801c02d626ee48a6b.camel@linux.ibm.com>
Date:   Thu, 27 Jan 2022 22:13:04 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>,
        Christian Brauner <brauner@...nel.org>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>
Cc:     linux-integrity@...r.kernel.org, serge@...lyn.com,
        christian.brauner@...ntu.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, jejb@...ux.ibm.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 v9 10/23] ima: Move IMA securityfs files into
 ima_namespace or onto stack

On Thu, 2022-01-27 at 12:02 -0500, Stefan Berger wrote:
> On 1/26/22 04:40, Christian Brauner wrote:
> > On Tue, Jan 25, 2022 at 05:46:32PM -0500, Stefan Berger wrote:
> >> From: Stefan Berger <stefanb@...ux.ibm.com>
> >>
> >> Only the securityfs IMA policy file is ever removed based on Kconfig
> >> options. For this reason, move the IMA securityfs policy file variable
> >> 'ima_policy' into the ima_namespace.
> >>
> >> Move the other IMA securityfs files onto the stack since they are not
> >> needed outside the function where they are created in. Also, their cleanup
> >> is automatically handled by the filesystem upon umount of a virtualized
> >> securityfs instance, so they don't need to be explicitly freed.
> > I'd reverse the explantion in the commit and mention the securityfs
> > change that makes this move possible which is patch 3 in this version of
> > the series ("securityfs: rework dentry creation"); something like:
> >
> > 	Earlier we simplified how dentry creation and deletion is manged in
> > 	securityfs. This allows us to move IMA securityfs files from global
> > 	variables directly into ima_fs_ns_init() itself. We can now rely on
> > 	those dentries to be cleaned up when the securityfs instance is cleaned
> > 	when the last reference to it is dropped.
> > 	
> > 	Things are slightly different for the initial ima namespace. In contrast
> > 	to non-initial ima namespaces it has pinning logic binding the lifetime
> > 	of the securityfs superblock to created dentries. We need to keep this
> > 	behavior to not regress userspace. Since ima never removes most of the
> > 	securityfs files the initial securityfs instance stays pinned. This also
> > 	means even for the initial ima namespace we don't need to keep
> > 	references to these dentries anywhere.
> > 	
> > 	The ima_policy file is the exception since ima can end up removing it if
> > 	a non-default policy is written at some point.
> >
> > Last sentence should be checked for sensibility by ima folks.
> 
> I remove the if clause and took the other text as-is...

Or replace it with, "on systems that don't allow reading or extending
the IMA custom policy."

thanks,

Mimi