(extra) check on storage event_id uuid-ness before using in filenames

events/storage.py

@@ -1,3 +1,4 @@
+import uuid
 import contextlib
 import os.path
 from pathlib import Path
@@ -41,6 +42,13 @@ class FileEventStorage(EventStorage):
     def _event_path(self, event_id):
         # the dashes in uuid are preserved in the filename for readability; since their location is consistent, this is
         # not a problem.
+
+        # event_id comes from event.id, i.e. it's a UUID object which is generated by Bugsink itself (i.e. trusted).
+        # The check below exists exclusively such that the security-implications of os.path.join can be understood right
+        # here in the code without needing to inspect all call-sites:
+        if not isinstance(event_id, uuid.UUID):
+            raise ValueError("event_id must be a UUID")
+
         return os.path.join(self.basepath, str(event_id) + ".json")
 
     @contextlib.contextmanager