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

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Message-ID: <b307ec62-7cfd-4a58-88ef-ea549c64e75e@schaufler-ca.com>
Date:   Tue, 24 Oct 2023 08:30:00 -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 10/24/2023 2:49 AM, Maxime Coquelin wrote:
>
>
> On 10/23/23 17:13, Casey Schaufler wrote:
>> 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.
>
> VDUSE is different from other devices as the device is actually
> implemented by the user-space application, so this is very specific in
> my opinion.

This is hardly unique. If you're implementing the device
in user-space you may well be able to implement the desired
controls there.

>
>>
>> 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.
>>
>
> I am not aware of such mechanism to deal with ioctl(), if you have a
> pointer that would be welcome.

security/selinux/hooks.c

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