Use admin.vm.List method to get VM class

Normally, VM class is cached when getting list of all (accessible)
VMs. This means the admin.vm.property.Get+klass is normally not used.
But if there is a case where VM object is created without listing all
VMs first, it will not get the 'klass' property set. Apparently
preloaded disposables trigger this case in audiovm.
The thing is, admin.vm.property.Get+klass is mostly redundant with
admin.vm.List (directed at a specific qube), since admin.vm.List
contains that information already - so it doesn't make much sense to
force everybody to add both to the policy.

Fix this by using admin.vm.List to get the VM class.

Fixes QubesOS/qubes-issues#10717

Author: marmarek

qubesadmin/tests/vm/properties.py

@@ -20,6 +20,7 @@
 
 # pylint: disable=missing-docstring
 
+import qubesadmin.vm
 import qubesadmin.tests.vm
 
 
@@ -305,3 +306,10 @@ def test_015_mem(self):
             ('test-vm', 'admin.vm.CurrentState', None, None)] = \
             b'0\x00mem=1234'
         self.assertEqual(self.vm.get_mem(), 1234)
+
+    def test_020_klass(self):
+        vm = qubesadmin.vm.QubesVM(self.app, "test-vm")
+        self.app.expected_calls[("test-vm", "admin.vm.List", None, None)] = \
+            b"0\x00test-vm class=AppVM state=Running\n"
+        self.assertEqual(vm.klass, "AppVM")
+        self.assertAllCalled()

qubesadmin/vm/__init__.py

@@ -446,8 +446,21 @@ def klass(self):
         """Qube class"""
         # use cached value if available
         if self._klass is None:
-            # pylint: disable=no-member
-            self._klass = super().klass
+            try:
+                # use List method as that should be allowed for VMs that are
+                # visible
+                vm_list_data = self.qubesd_call(
+                    self._method_dest, "admin.vm.List"
+                )
+                assert vm_list_data.count(b"\n") == 1
+                vm_name, props = vm_list_data.decode("ascii").split(" ", 1)
+                assert vm_name == self.name
+                props = props.split(" ")
+                props_dict = dict([vm_prop.split("=", 1) for vm_prop in props])
+                self._klass = props_dict["class"]
+            except qubesadmin.exc.QubesDaemonAccessError:
+                # pylint: disable=no-member
+                self._klass = super().klass
         return self._klass
 
     def get_notes(self) -> str: