Avoid mutating cached room aliases. (#15038)

clokep · web-flow · commit 8a6e0434889e · 2023-02-09T15:56:02.000Z
This might cause incorrect data in other callers which
are not expecting the canonical alias to be added into
the response.
diff --git a/changelog.d/15038.bugfix b/changelog.d/15038.bugfix
@@ -0,0 +1 @@
+Fix a long-standing bug where the room aliases returned could be corrupted.
diff --git a/synapse/handlers/directory.py b/synapse/handlers/directory.py
@@ -485,7 +485,8 @@ async def edit_published_room_list(
                 )
             )
             if canonical_alias:
-                room_aliases.append(canonical_alias)
+                # Ensure we do not mutate room_aliases.
+                room_aliases = room_aliases + [canonical_alias]
 
             if not self.config.roomdirectory.is_publishing_room_allowed(
                 user_id, room_id, room_aliases

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+Fix a long-standing bug where the room aliases returned could be corrupted.`
Original file line number	Diff line number	Diff line change
`@@ -485,7 +485,8 @@ async def edit_published_room_list(`
`485`	`485`	`)`
`486`	`486`	`)`
`487`	`487`	`if canonical_alias:`
`488`		`- room_aliases.append(canonical_alias)`
	`488`	`+ # Ensure we do not mutate room_aliases.`
	`489`	`+ room_aliases = room_aliases + [canonical_alias]`
`489`	`490`
`490`	`491`	`if not self.config.roomdirectory.is_publishing_room_allowed(`
`491`	`492`	`user_id, room_id, room_aliases`