Linux Virtualization - Oct 2023 - [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 at
kernel.org/
>

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 at
kernel.org/
>>
>