linux-kernel - Re: [RFC 20/20] ima: Setup securityfs

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Date:   Wed, 01 Dec 2021 17:19:03 -0500
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>,
        linux-integrity@...r.kernel.org
Cc:     zohar@...ux.ibm.com, 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, 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: [RFC 20/20] ima: Setup securityfs_ns for IMA namespace

On Wed, 2021-12-01 at 17:09 -0500, Stefan Berger wrote:
> On 12/1/21 17:01, James Bottomley wrote:
[...]
> > OK, I think I figured it out.  When I applied your patches, it was
> > on top of my existing ones, so I had to massage them a bit.
> > 
> > Your problem is the securityfs inode creation is triggered inside
> > create_user_ns, which means it happens *before* ushare writes to
> > the proc/self/uid_map file, so the securityfs_inodes are always
> > created on an empty mapping and i_write_uid always sets the inode
> > uid to -1.
> 
> Right, the initialization of the filesystem is quite early.
> 
> 
> > I don't see this because my setup for everything is triggered off
> > the first use of the IMA namespace.  You'd need to have some type
> > of lazy setup of the inodes as well to give unshare time to install
> > the uid/gidmappings.
> 
> What could trigger that? A callback while mounting - but I am not
> sure where to hook into then. What is your mechanisms to trigger as
> the 'first use of the IMA namespace'? What is 'use' here?

use for me is first event that gets logged in the new namespace.

However, I don't think this is a good trigger, it's just a random thing
I was playing with.  Perhaps trigger on mount is a good one ... that
could be done from securityfs_ns_init_fs_context?

James