Linux Virtualization - Oct 2023 - [PATCH v4 4/4] vduse: Add LSM hooks to check Virtio device type

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/
>>
>

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 at
kernel.org/
>>>
>>>
>>
>