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Date:   Thu, 2 Nov 2023 18:56:59 +0100
From:   Maxime Coquelin <maxime.coquelin@...hat.com>
To:     Casey Schaufler <casey@...aufler-ca.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
Subject: Re: [PATCH v4 4/4] vduse: Add LSM hooks to check Virtio device type



On 10/24/23 17:30, Casey Schaufler wrote:
> 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

We might be able to extend selinux_file_ioctl(), but that will only
covers the ioctl for the control file, this patch also adds hook for the
device file opening that would need dedicated hook as the device type
information is stored in the device's private data.

Michael, before going further, I would be interested in your feedback.
Was this patch what you had in mind when requesting for a way to
allow/deny devices types for a given application?

Regards,
Maxime

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

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