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

[Maxime Coquelin <maxime.coquelin@redhat.com>]

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.

> 
> 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.

Thanks,
Maxime

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