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

[Michael S. Tsirkin]

On Thu, Nov 02, 2023 at 06:56:59PM +0100, Maxime Coquelin wrote:
> 
> 
> 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


Yes, this is more or less what I had in mind.

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