From 47e28b4031c7c5e2c87824c2b4873492b996d02e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dagfinn=20Ilmari=20Manns=C3=A5ker?= <ilmari@ilmari.org>
Date: Tue, 6 Jul 2021 14:31:13 +0100
Subject: [PATCH] Ignore EDUs for rooms we're not in (#10317)

---
 changelog.d/10317.bugfix      |  1 +
 synapse/handlers/receipts.py  | 15 ++++++++++++++
 synapse/handlers/typing.py    | 14 +++++++++++++
 tests/handlers/test_typing.py | 37 +++++++++++++++++++++++++++++++++++
 4 files changed, 67 insertions(+)
 create mode 100644 changelog.d/10317.bugfix

diff --git a/changelog.d/10317.bugfix b/changelog.d/10317.bugfix
new file mode 100644
index 0000000000..826c269eff
--- /dev/null
+++ b/changelog.d/10317.bugfix
@@ -0,0 +1 @@
+Fix purging rooms that other homeservers are still sending events for. Contributed by @ilmari.
diff --git a/synapse/handlers/receipts.py b/synapse/handlers/receipts.py
index f782d9db32..0059ad0f56 100644
--- a/synapse/handlers/receipts.py
+++ b/synapse/handlers/receipts.py
@@ -30,6 +30,8 @@ class ReceiptsHandler(BaseHandler):
 
         self.server_name = hs.config.server_name
         self.store = hs.get_datastore()
+        self.event_auth_handler = hs.get_event_auth_handler()
+
         self.hs = hs
 
         # We only need to poke the federation sender explicitly if its on the
@@ -59,6 +61,19 @@ class ReceiptsHandler(BaseHandler):
         """Called when we receive an EDU of type m.receipt from a remote HS."""
         receipts = []
         for room_id, room_values in content.items():
+            # If we're not in the room just ditch the event entirely. This is
+            # probably an old server that has come back and thinks we're still in
+            # the room (or we've been rejoined to the room by a state reset).
+            is_in_room = await self.event_auth_handler.check_host_in_room(
+                room_id, self.server_name
+            )
+            if not is_in_room:
+                logger.info(
+                    "Ignoring receipt from %s as we're not in the room",
+                    origin,
+                )
+                continue
+
             for receipt_type, users in room_values.items():
                 for user_id, user_values in users.items():
                     if get_domain_from_id(user_id) != origin:
diff --git a/synapse/handlers/typing.py b/synapse/handlers/typing.py
index e22393adc4..c0a8364755 100644
--- a/synapse/handlers/typing.py
+++ b/synapse/handlers/typing.py
@@ -208,6 +208,7 @@ class TypingWriterHandler(FollowerTypingHandler):
 
         self.auth = hs.get_auth()
         self.notifier = hs.get_notifier()
+        self.event_auth_handler = hs.get_event_auth_handler()
 
         self.hs = hs
 
@@ -326,6 +327,19 @@ class TypingWriterHandler(FollowerTypingHandler):
         room_id = content["room_id"]
         user_id = content["user_id"]
 
+        # If we're not in the room just ditch the event entirely. This is
+        # probably an old server that has come back and thinks we're still in
+        # the room (or we've been rejoined to the room by a state reset).
+        is_in_room = await self.event_auth_handler.check_host_in_room(
+            room_id, self.server_name
+        )
+        if not is_in_room:
+            logger.info(
+                "Ignoring typing update from %s as we're not in the room",
+                origin,
+            )
+            return
+
         member = RoomMember(user_id=user_id, room_id=room_id)
 
         # Check that the string is a valid user id
diff --git a/tests/handlers/test_typing.py b/tests/handlers/test_typing.py
index f58afbc244..fa3cff598e 100644
--- a/tests/handlers/test_typing.py
+++ b/tests/handlers/test_typing.py
@@ -38,6 +38,9 @@ U_ONION = UserID.from_string("@onion:farm")
 # Test room id
 ROOM_ID = "a-room"
 
+# Room we're not in
+OTHER_ROOM_ID = "another-room"
+
 
 def _expect_edu_transaction(edu_type, content, origin="test"):
     return {
@@ -115,6 +118,11 @@ class TypingNotificationsTestCase(unittest.HomeserverTestCase):
 
         hs.get_auth().check_user_in_room = check_user_in_room
 
+        async def check_host_in_room(room_id, server_name):
+            return room_id == ROOM_ID
+
+        hs.get_event_auth_handler().check_host_in_room = check_host_in_room
+
         def get_joined_hosts_for_room(room_id):
             return {member.domain for member in self.room_members}
 
@@ -244,6 +252,35 @@ class TypingNotificationsTestCase(unittest.HomeserverTestCase):
             ],
         )
 
+    def test_started_typing_remote_recv_not_in_room(self):
+        self.room_members = [U_APPLE, U_ONION]
+
+        self.assertEquals(self.event_source.get_current_key(), 0)
+
+        channel = self.make_request(
+            "PUT",
+            "/_matrix/federation/v1/send/1000000",
+            _make_edu_transaction_json(
+                "m.typing",
+                content={
+                    "room_id": OTHER_ROOM_ID,
+                    "user_id": U_ONION.to_string(),
+                    "typing": True,
+                },
+            ),
+            federation_auth_origin=b"farm",
+        )
+        self.assertEqual(channel.code, 200)
+
+        self.on_new_event.assert_not_called()
+
+        self.assertEquals(self.event_source.get_current_key(), 0)
+        events = self.get_success(
+            self.event_source.get_new_events(room_ids=[OTHER_ROOM_ID], from_key=0)
+        )
+        self.assertEquals(events[0], [])
+        self.assertEquals(events[1], 0)
+
     @override_config({"send_federation": True})
     def test_stopped_typing(self):
         self.room_members = [U_APPLE, U_BANANA, U_ONION]