Add support for MSC4293 - Redact on Kick/Ban

changelog.d/18540.feature

@@ -0,0 +1 @@
+Add support for [MSC4293](https://github.com/matrix-org/matrix-spec-proposals/pull/4293) - Redact on Kick/Ban.

synapse/config/experimental.py

@@ -569,3 +569,6 @@ def read_config(
 
         # MSC4155: Invite filtering
         self.msc4155_enabled: bool = experimental.get("msc4155_enabled", False)
+
+        # MSC4293: Redact on Kick/Ban
+        self.msc4293_enabled: bool = experimental.get("msc4293_enabled", False)

synapse/handlers/federation_event.py

@@ -1966,6 +1966,9 @@ async def _check_for_soft_fail(
         Does nothing for events in rooms with partial state, since we may not have an
         accurate membership event for the sender in the current state.
 
+        Also checks if event should be redacted due to a MSC4293 redaction flag in kick/ban
+        event for user
+
         Args:
             event
             context: The `EventContext` which we are about to persist the event with.
@@ -2065,6 +2068,79 @@ async def _check_for_soft_fail(
             soft_failed_event_counter.inc()
             event.internal_metadata.soft_failed = True
 
+        if not self._config.experimental.msc4293_enabled:
+            return
+        # Use already calculated auth events to determine if the event should be redacted due to kick/ban
+        pl_event = None
+        for auth_e in current_auth_events:
+            if auth_e.type == EventTypes.PowerLevels:
+                pl_event = auth_e
+                break
+        # this should never happen but just in case
+        if pl_event is None:
+            return
+        if event.type in [EventTypes.Message, EventTypes.Encrypted, EventTypes.Member]:
+            for auth_event in current_auth_events:
+                if auth_event.get("state_key") is None:
+                    continue
+                if (
+                    auth_event.type != EventTypes.Member
+                    or auth_event.state_key != event.sender
+                ):
+                    continue
+                if auth_event.membership not in [Membership.LEAVE, Membership.BAN]:
+                    continue
+                # self-bans currently are not authorized so we don't check for that
+                # case
+                if (
+                    auth_event.membership == Membership.LEAVE
+                    and auth_event.sender == auth_event.state_key
+                ):
+                    continue
+                # we have a ban or kick for this sender,
+                # check for redaction flag and apply if found
+                autoredact = auth_event.content.get(
+                    "org.matrix.msc4293.redact_events", False
+                )
+                if not autoredact or not isinstance(autoredact, bool):
+                    continue
+
+                # check that the sender of the kick/ban can redact
+                sender_level = pl_event.content.get("users", {}).get(auth_event.sender)
+                if sender_level is None:
+                    sender_level = pl_event.content.get("users_default", 0)
+
+                redact_level = pl_event.content.get("redact", 50)
+                room_redaction_level = pl_event.content.get("events", {}).get(
+                    "m.room.redaction"
+                )
+                if room_redaction_level:
+                    if sender_level < room_redaction_level:
+                        continue
+
+                if sender_level > redact_level:
+                    # copy through the redacting event
+                    event.unsigned["redacted_because"] = auth_event.get_dict()
+                    await self._store.db_pool.simple_upsert(
+                        table="redactions",
+                        keyvalues={
+                            "event_id": auth_event.event_id,
+                            "redacts": event.event_id,
+                        },
+                        values={"received_ts": self._clock.time_msec()},
+                        insertion_values={
+                            "event_id": auth_event.event_id,
+                            "redacts": event.event_id,
+                            "received_ts": self._clock.time_msec(),
+                        },
+                    )
+                    await self._store.db_pool.runInteraction(
+                        "invalidate cache",
+                        self._store.invalidate_get_event_cache_after_txn,
+                        event.event_id,
+                    )
+                    break
+
     async def _load_or_fetch_auth_events_for_event(
         self, destination: Optional[str], event: EventBase
     ) -> Collection[EventBase]:

synapse/rest/client/room.py

@@ -1088,6 +1088,7 @@ def __init__(self, hs: "HomeServer"):
         super().__init__(hs)
         self.room_member_handler = hs.get_room_member_handler()
         self.auth = hs.get_auth()
+        self.config = hs.config
 
     def register(self, http_server: HttpServer) -> None:
         # /rooms/$roomid/[join|invite|leave|ban|unban|kick]
@@ -1111,12 +1112,12 @@ async def _do(
         }:
             raise AuthError(403, "Guest access not allowed")
 
-        content = parse_json_object_from_request(request, allow_empty_body=True)
+        request_body = parse_json_object_from_request(request, allow_empty_body=True)
 
         if membership_action == "invite" and all(
-            key in content for key in ("medium", "address")
+            key in request_body for key in ("medium", "address")
         ):
-            if not all(key in content for key in ("id_server", "id_access_token")):
+            if not all(key in request_body for key in ("id_server", "id_access_token")):
                 raise SynapseError(
                     HTTPStatus.BAD_REQUEST,
                     "`id_server` and `id_access_token` are required when doing 3pid invite",
@@ -1127,12 +1128,12 @@ async def _do(
                 await self.room_member_handler.do_3pid_invite(
                     room_id,
                     requester.user,
-                    content["medium"],
-                    content["address"],
-                    content["id_server"],
+                    request_body["medium"],
+                    request_body["address"],
+                    request_body["id_server"],
                     requester,
                     txn_id,
-                    content["id_access_token"],
+                    request_body["id_access_token"],
                 )
             except ShadowBanError:
                 # Pretend the request succeeded.
@@ -1141,12 +1142,19 @@ async def _do(
 
         target = requester.user
         if membership_action in ["invite", "ban", "unban", "kick"]:
-            assert_params_in_dict(content, ["user_id"])
-            target = UserID.from_string(content["user_id"])
+            assert_params_in_dict(request_body, ["user_id"])
+            target = UserID.from_string(request_body["user_id"])
 
         event_content = None
-        if "reason" in content:
-            event_content = {"reason": content["reason"]}
+        if "reason" in request_body:
+            event_content = {"reason": request_body["reason"]}
+        if self.config.experimental.msc4293_enabled:
+            if "org.matrix.msc4293.redact_events" in request_body:
+                if event_content is None:
+                    event_content = {}
+                event_content["org.matrix.msc4293.redact_events"] = request_body[
+                    "org.matrix.msc4293.redact_events"
+                ]
 
         try:
             await self.room_member_handler.update_membership(
@@ -1155,7 +1163,7 @@ async def _do(
                 room_id=room_id,
                 action=membership_action,
                 txn_id=txn_id,
-                third_party_signed=content.get("third_party_signed", None),
+                third_party_signed=request_body.get("third_party_signed", None),
                 content=event_content,
             )
         except ShadowBanError:

synapse/storage/databases/main/events.py

@@ -376,6 +376,89 @@ async def _persist_events_and_state_updates(
 
                 event_counter.labels(event.type, origin_type, origin_entity).inc()
 
+                # check for msc4293 redact_events flag and apply if found
+                if (
+                    not self.hs.config.experimental.msc4293_enabled
+                    or event.type != EventTypes.Member
+                ):
+                    continue
+                if event.membership not in [Membership.LEAVE, Membership.BAN]:
+                    continue
+                redact = event.content.get("org.matrix.msc4293.redact_events", False)
+                if not redact or not isinstance(redact, bool):
+                    continue
+                # self-bans currently are not authorized so we don't check for that
+                # case
+                if (
+                    event.membership == Membership.LEAVE
+                    and event.sender == event.state_key
+                ):
+                    continue
+                # check that sender can redact
+                state_filter = StateFilter.from_types([(EventTypes.PowerLevels, "")])
+                state = await self.store.get_partial_filtered_current_state_ids(
+                    event.room_id, state_filter
+                )
+                pl_id = state[(EventTypes.PowerLevels, "")]
+                pl_event = await self.store.get_event(pl_id)
+                if pl_event:
+                    sender_level = pl_event.content.get("users", {}).get(event.sender)
+                    if sender_level is None:
+                        sender_level = pl_event.content.get("users_default", 0)
+                    redact_level = pl_event.content.get("redact", 50)
+
+                    room_redaction_level = pl_event.content.get("events", {}).get(
+                        "m.room.redaction"
+                    )
+                    if room_redaction_level:
+                        if sender_level < room_redaction_level:
+                            continue
+
+                    if sender_level > redact_level:
+                        ids_to_redact = (
+                            await self.store.get_events_sent_by_user_in_room(
+                                event.state_key,
+                                event.room_id,
+                                limit=1000000,  # arbitrarily large number
+                                filter=[
+                                    EventTypes.Member,
+                                    EventTypes.Message,
+                                    EventTypes.Encrypted,
+                                ],
+                            )
+                        )
+                        if not ids_to_redact:
+                            continue
+
+                        key_values = [(event.event_id, x) for x in ids_to_redact]
+                        value_values = [
+                            (self._clock.time_msec(),) for x in ids_to_redact
+                        ]
+                        await self.db_pool.simple_upsert_many(
+                            table="redactions",
+                            key_names=["event_id", "redacts"],
+                            key_values=key_values,
+                            value_names=["received_ts"],
+                            value_values=value_values,
+                            desc="redact_on_ban_redaction_txn",
+                        )
+
+                        redacted_events = await self.store.get_events_as_list(
+                            ids_to_redact
+                        )
+                        for redacted_event in redacted_events:
+                            redacted_event.unsigned["redacted_because"] = event
+
+                        # normally the cache entry for a redacted event would be invalidated
+                        # by an arriving redaction event, but since we are not creating redaction
+                        # events we invalidate manually
+                        for id in ids_to_redact:
+                            await self.db_pool.runInteraction(
+                                "invalidate cache",
+                                self.store.invalidate_get_event_cache_after_txn,
+                                id,
+                            )
+
             if new_forward_extremities:
                 self.store.get_latest_event_ids_in_room.prefill(
                     (room_id,), frozenset(new_forward_extremities)
@@ -2768,9 +2851,8 @@ def _store_redaction(self, txn: LoggingTransaction, event: EventBase) -> None:
         self.db_pool.simple_upsert_txn(
             txn,
             table="redactions",
-            keyvalues={"event_id": event.event_id},
+            keyvalues={"event_id": event.event_id, "redacts": event.redacts},
             values={
-                "redacts": event.redacts,
                 "received_ts": self._clock.time_msec(),
             },
         )

synapse/storage/databases/main/room.py

@@ -1962,6 +1962,28 @@ def __init__(
     ):
         super().__init__(database, db_conn, hs)
 
+        self.db_pool.updates.register_background_index_update(
+            "redactions_add_event_id_idx",
+            "redactions_event_id",
+            "redactions",
+            ["event_id"],
+        )
+
+        self.db_pool.updates.register_background_index_update(
+            "redactions_add_redacts_idx",
+            "redactions_redacts",
+            "redactions",
+            ["redacts"],
+        )
+
+        self.db_pool.updates.register_background_index_update(
+            "redactions_add_have_censored_ts",
+            "redactions_have_censored_ts",
+            "redactions",
+            ["received_ts"],
+            where_clause="NOT have_censored",
+        )
+
         self.db_pool.updates.register_background_update_handler(
             "insert_room_retention",
             self._background_insert_retention,

synapse/storage/schema/main/delta/92/06_redactions_multitarget.py

@@ -0,0 +1,72 @@
+from synapse.storage.database import LoggingTransaction
+from synapse.storage.engines import BaseDatabaseEngine, PostgresEngine
+
+
+def run_create(
+    cur: LoggingTransaction,
+    database_engine: BaseDatabaseEngine,
+) -> None:
+    """
+    Drop unique constraint event_id and add unique constraint (event_id, redacts)
+    """
+    if isinstance(database_engine, PostgresEngine):
+        add_constraint_sql = """
+        ALTER TABLE ONLY redactions ADD CONSTRAINT redactions_event_id_redacts_key UNIQUE (event_id, redacts);
+        """
+        cur.execute(add_constraint_sql)
+
+        drop_constraint_sql = """
+        ALTER TABLE ONLY redactions DROP CONSTRAINT redactions_event_id_key;
+        """
+        cur.execute(drop_constraint_sql)
+
+    else:
+        # in SQLite we need to rewrite the table to change the constraint.
+        # First drop any temporary table that might be here from a previous failed migration.
+        cur.execute("DROP TABLE IF EXISTS temp_redactions")
+
+        create_sql = """
+        CREATE TABLE temp_redactions (
+            event_id TEXT NOT NULL,
+            redacts TEXT NOT NULL,
+            have_censored BOOL NOT NULL DEFAULT false,
+            received_ts BIGINT,
+            UNIQUE(event_id, redacts)
+        );
+        """
+        cur.execute(create_sql)
+
+        copy_sql = """
+        INSERT INTO temp_redactions (
+            event_id,
+            redacts,
+            have_censored,
+            received_ts
+        ) SELECT r.event_id, r.redacts, r.have_censored, r.received_ts FROM redactions AS r;
+        """
+        cur.execute(copy_sql)
+
+        drop_sql = """
+        DROP TABLE redactions
+        """
+        cur.execute(drop_sql)
+
+        rename_sql = """
+        ALTER TABLE temp_redactions RENAME to redactions
+        """
+        cur.execute(rename_sql)
+
+        sqlite3_idx_update_sql = """
+             INSERT INTO background_updates (ordering, update_name, progress_json) \
+             VALUES (?, ?, ?);
+         """
+        cur.execute(sqlite3_idx_update_sql, (9206, "redactions_add_redacts_idx", "{}"))
+        cur.execute(
+            sqlite3_idx_update_sql, (9206, "redactions_add_have_censored_ts", "{}")
+        )
+
+    # in either case the event_id index needs to be re-created
+    idx_sql = """
+          INSERT INTO background_updates (ordering, update_name, progress_json) VALUES (?, ?, ?);
+    """
+    cur.execute(idx_sql, (9206, "redactions_add_event_id_idx", "{}"))