From 7b06f85c0e18b62775f12789fdf4adb6a0a47a4b Mon Sep 17 00:00:00 2001
From: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Date: Wed, 17 Mar 2021 16:51:55 +0000
Subject: Ensure we use a copy of the event content dict before modifying it in
 serialize_event (#9585)

This bug was discovered by DINUM. We were modifying `serialized_event["content"]`, which - if you've got `USE_FROZEN_DICTS` turned on or are [using a third party rules module](https://github.com/matrix-org/synapse/blob/17cd48fe5171d50da4cb59db647b993168e7dfab/synapse/events/third_party_rules.py#L73-L76) - will raise a 500 if you try to a edit a reply to a message.

`serialized_event["content"]` could be set to the edit event's content, instead of a copy of it, which is bad as we attempt to modify it. Instead, we also end up modifying the original event's content. DINUM uses a third party rules module, which meant the event's content got frozen and thus an exception was raised.

To be clear, the problem is not that the event's content was frozen. In fact doing so helped us uncover the fact we weren't copying event content correctly.
---
 tests/rest/client/test_third_party_rules.py | 62 +++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

(limited to 'tests/rest/client/test_third_party_rules.py')

diff --git a/tests/rest/client/test_third_party_rules.py b/tests/rest/client/test_third_party_rules.py
index 227fffab58..bf39014277 100644
--- a/tests/rest/client/test_third_party_rules.py
+++ b/tests/rest/client/test_third_party_rules.py
@@ -161,6 +161,68 @@ class ThirdPartyRulesTestCase(unittest.HomeserverTestCase):
         ev = channel.json_body
         self.assertEqual(ev["content"]["x"], "y")
 
+    def test_message_edit(self):
+        """Ensure that the module doesn't cause issues with edited messages."""
+        # first patch the event checker so that it will modify the event
+        async def check(ev: EventBase, state):
+            d = ev.get_dict()
+            d["content"] = {
+                "msgtype": "m.text",
+                "body": d["content"]["body"].upper(),
+            }
+            return d
+
+        current_rules_module().check_event_allowed = check
+
+        # Send an event, then edit it.
+        channel = self.make_request(
+            "PUT",
+            "/_matrix/client/r0/rooms/%s/send/modifyme/1" % self.room_id,
+            {
+                "msgtype": "m.text",
+                "body": "Original body",
+            },
+            access_token=self.tok,
+        )
+        self.assertEqual(channel.result["code"], b"200", channel.result)
+        orig_event_id = channel.json_body["event_id"]
+
+        channel = self.make_request(
+            "PUT",
+            "/_matrix/client/r0/rooms/%s/send/m.room.message/2" % self.room_id,
+            {
+                "m.new_content": {"msgtype": "m.text", "body": "Edited body"},
+                "m.relates_to": {
+                    "rel_type": "m.replace",
+                    "event_id": orig_event_id,
+                },
+                "msgtype": "m.text",
+                "body": "Edited body",
+            },
+            access_token=self.tok,
+        )
+        self.assertEqual(channel.result["code"], b"200", channel.result)
+        edited_event_id = channel.json_body["event_id"]
+
+        # ... and check that they both got modified
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/r0/rooms/%s/event/%s" % (self.room_id, orig_event_id),
+            access_token=self.tok,
+        )
+        self.assertEqual(channel.result["code"], b"200", channel.result)
+        ev = channel.json_body
+        self.assertEqual(ev["content"]["body"], "ORIGINAL BODY")
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/r0/rooms/%s/event/%s" % (self.room_id, edited_event_id),
+            access_token=self.tok,
+        )
+        self.assertEqual(channel.result["code"], b"200", channel.result)
+        ev = channel.json_body
+        self.assertEqual(ev["content"]["body"], "EDITED BODY")
+
     def test_send_event(self):
         """Tests that the module can send an event into a room via the module api"""
         content = {
-- 
cgit 1.5.1