Do not use assert statement in security logic

This is because assert statement gets optimised out when Python is run with -O flag. This was pointed out to me by audience at PyWaw 76.
marmarek · Jun 11, 2018 · 4e49b95 · 4e49b95
1 parent 39a9e4e
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diff --git a/qubes/api/__init__.py b/qubes/api/__init__.py
@@ -196,6 +196,11 @@ def fire_event_for_filter(self, iterable, **kwargs):
         return apply_filters(iterable,
             self.fire_event_for_permission(**kwargs))
 
+    def enforce(self, predicate):
+        '''An assert replacement, but works even with optimisations.'''
+        if not predicate:
+            raise PermissionDenied()
+
 
 class QubesDaemonProtocol(asyncio.Protocol):
     buffer_size = 65536