linux-kernel - Re: [PATCH v4 4/4] vduse: Add LSM hooks to check Virtio device type

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Message-ID: <64626db9-e37a-4c65-a455-fc3985382216@schaufler-ca.com>
Date:   Mon, 23 Oct 2023 08:13:35 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Maxime Coquelin <maxime.coquelin@...hat.com>, mst@...hat.com,
        jasowang@...hat.com, xuanzhuo@...ux.alibaba.com,
        paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        xieyongji@...edance.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        david.marchand@...hat.com, lulu@...hat.com,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v4 4/4] vduse: Add LSM hooks to check Virtio device type

On 10/23/2023 12:28 AM, Maxime Coquelin wrote:
>
>
> On 10/21/23 00:20, Casey Schaufler wrote:
>> On 10/20/2023 8:58 AM, Maxime Coquelin wrote:
>>> This patch introduces LSM hooks for devices creation,
>>> destruction and opening operations, checking the
>>> application is allowed to perform these operations for
>>> the Virtio device type.
>>
>> Why do you think that there needs to be a special LSM check for virtio
>> devices? What can't existing device attributes be used?
>
> Michael asked for a way for SELinux to allow/prevent the creation of
> some types of devices [0].
>
> A device is created using ioctl() on VDUSE control chardev. Its type is
> specified via a field in the structure passed in argument.
>
> I didn't see other way than adding dedicated LSM hooks to achieve this,
> but it is possible that their is a better way to do it?

At the very least the hook should be made more general, and I'd have to
see a proposal before commenting on that. security_dev_destroy(dev) might
be a better approach. If there's reason to control destruction of vduse
devices it's reasonable to assume that there are other devices with the
same or similar properties.

Since SELinux is your target use case, can you explain why you can't
create SELinux policy to enforce the restrictions you're after? I believe
(but can be proven wrong, of course) that SELinux has mechanism for dealing
with controls on ioctls.


>
> Thanks,
> Maxime
>
> [0]:
> https://lore.kernel.org/all/20230829130430-mutt-send-email-mst@kernel.org/
>