linux-kernel - Re: [PATCH v10 22/27] securityfs: Extend securityfs with namespacing support

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Message-ID: <bfd9878c-71d5-1a9e-6306-b2cc68b26772@linux.ibm.com>
Date:   Wed, 23 Feb 2022 10:44:28 -0500
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     Christian Brauner <brauner@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>
Cc:     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, 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,
        James Bottomley <James.Bottomley@...senPartnership.com>
Subject: Re: [PATCH v10 22/27] securityfs: Extend securityfs with namespacing
 support


On 2/23/22 03:14, Christian Brauner wrote:
> On Tue, Feb 22, 2022 at 08:48:47PM -0500, Mimi Zohar wrote:
>> On Tue, 2022-02-01 at 15:37 -0500, Stefan Berger wrote:
>>> Enable multiple instances of securityfs by keying each instance with a
>>> pointer to the user namespace it belongs to.
>>>
>>> Since we do not need the pinning of the filesystem for the virtualization
>> ^namespacing case
>>
>>> case, limit the usage of simple_pin_fs() and simpe_release_fs() to the
>> ^simple_release_fs
>>
>>> case when the init_user_ns is active. This simplifies the cleanup for the
>>> virtualization case where usage of securityfs_remove() to free dentries
>> ^namespacing
>>
>>> is therefore not needed anymore.
>>>
>>> For the initial securityfs, i.e. the one mounted in the host userns mount,
>>> nothing changes. The rules for securityfs_remove() are as before and it is
>>> still paired with securityfs_create(). Specifically, a file created via
>>> securityfs_create_dentry() in the initial securityfs mount still needs to
>>> be removed by a call to securityfs_remove(). Creating a new dentry in the
>>> initial securityfs mount still pins the filesystem like it always did.
>>> Consequently, the initial securityfs mount is not destroyed on
>>> umount/shutdown as long as at least one user of it still has dentries that
>>> it hasn't removed with a call to securityfs_remove().
>>>
>>> Prevent mounting of an instance of securityfs in another user namespace
>>> than it belongs to. Also, prevent accesses to files and directories by
>>> a user namespace that is neither the user namespace it belongs to
>>> nor an ancestor of the user namespace that the instance of securityfs
>>> belongs to. Do not prevent access if securityfs was bind-mounted and
>>> therefore the init_user_ns is the owning user namespace.
>>>
>>> Suggested-by: Christian Brauner <brauner@...nel.org>
>>> Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
>>> Signed-off-by: James Bottomley <James.Bottomley@...senPartnership.com>
>> Christian, I understand that "[PATCH v10 23/27] ima: Setup securityfs
>> for IMA namespace" needs to be deferred, but is there a reason for
>> deferring  "[PATCH v10 22/27] securityfs: Extend securityfs with
>> namespacing support"?   As the securityfs patches are really
>> independent of IMA namespacing, I would have thought  "[PATCH v10
>> 04/27] securityfs: rework dentry creation" and this patch should be co-
>> located at the beginning of the patch set.
> It felt more natural to me to defer it until the end but I have no
> strong thoughts on this as of right now. Since Stefan has mentioned
> moving this earlier already himself and you seem to agree as well, feel
> free to do so.

I'll move it after 'securityfs: rework dentry creation' if that's ok.

    Stefan