mgmt: implement mgmt.vm.property.Set

Sanitization of input value is tricky here, and also very important at
the same time. If property define value type (and it's something more
specific than 'str'), use that. Otherwise allow only printable ASCII
characters, and let appropriate event and setter handle value.
At this point I've reviewed all QubesVM properties in this category and
added appropriate setters where needed.

QubesOS/qubes-issues#2622

qubes/mgmt.py

@@ -188,6 +188,53 @@ class QubesMgmt(object):
                 property_type,
                 str(value) if value is not None else '')
 
+    @asyncio.coroutine
+    def vm_property_set(self, untrusted_payload):
+        assert self.arg in self.dest.property_list()
+
+        property_def = self.dest.property_get_def(self.arg)
+        # do not treat type='str' as sufficient validation
+        if isinstance(property_def, qubes.vm.VMProperty):
+            try:
+                untrusted_vmname = untrusted_payload.decode('ascii')
+            except UnicodeDecodeError:
+                raise qubes.exc.QubesValueError
+            qubes.vm.qubesvm.validate_name(self.dest, property_def,
+                untrusted_vmname)
+            try:
+                newvalue = self.app.domains[untrusted_vmname]
+            except KeyError:
+                raise qubes.exc.QubesPropertyValueError(
+                    self.dest, property_def, untrusted_vmname)
+        elif property_def.type is not None and property_def.type is not str:
+            if property_def.type is bool:
+                try:
+                    untrusted_value = untrusted_payload.decode('ascii')
+                except UnicodeDecodeError:
+                    raise qubes.exc.QubesValueError
+                newvalue = qubes.property.bool(None, None, untrusted_value)
+            else:
+                try:
+                    newvalue = property_def.type(untrusted_payload)
+                except ValueError:
+                    raise qubes.exc.QubesValueError
+        else:
+            # other types (including explicitly defined 'str') coerce to str
+            # with limited characters allowed
+            try:
+                untrusted_value = untrusted_payload.decode('ascii')
+            except UnicodeDecodeError:
+                raise qubes.exc.QubesValueError
+            allowed_set = string.printable
+            if not all(x in allowed_set for x in untrusted_value):
+                raise qubes.exc.QubesValueError(
+                    'Invalid characters in property value')
+            newvalue = untrusted_value
+
+        self.fire_event_for_permission(newvalue=newvalue)
+
+        setattr(self.dest, self.arg, newvalue)
+
     @asyncio.coroutine
     def vm_property_help(self, untrusted_payload):
         assert self.arg in self.dest.property_list()