Allow deleting an alias if the user has sufficient power level (#6986)

* commit '13892776e':
  Allow deleting an alias if the user has sufficient power level (#6986)

changelog.d/6986.feature

@@ -0,0 +1 @@
+Users with a power level sufficient to modify the canonical alias of a room can now delete room aliases.

synapse/api/auth.py

@@ -544,7 +544,7 @@ def compute_auth_events(
 
     @defer.inlineCallbacks
     def check_can_change_room_list(self, room_id: str, user: UserID):
-        """Check if the user is allowed to edit the room's entry in the
+        """Determine whether the user is allowed to edit the room's entry in the
         published room list.
 
         Args:
@@ -575,12 +575,7 @@ def check_can_change_room_list(self, room_id: str, user: UserID):
         )
         user_level = event_auth.get_user_power_level(user_id, auth_events)
 
-        if user_level < send_level:
-            raise AuthError(
-                403,
-                "This server requires you to be a moderator in the room to"
-                " edit its room list entry",
-            )
+        return user_level >= send_level
 
     @staticmethod
     def has_access_token(request):

synapse/handlers/directory.py

@@ -15,7 +15,7 @@
 
 import logging
 import string
-from typing import List
+from typing import Iterable, List, Optional
 
 from twisted.internet import defer
 
@@ -28,6 +28,7 @@
     StoreError,
     SynapseError,
 )
+from synapse.appservice import ApplicationService
 from synapse.types import Requester, RoomAlias, UserID, get_domain_from_id
 
 from ._base import BaseHandler
@@ -55,7 +56,13 @@ def __init__(self, hs):
         self.spam_checker = hs.get_spam_checker()
 
     @defer.inlineCallbacks
-    def _create_association(self, room_alias, room_id, servers=None, creator=None):
+    def _create_association(
+        self,
+        room_alias: RoomAlias,
+        room_id: str,
+        servers: Optional[Iterable[str]] = None,
+        creator: Optional[str] = None,
+    ):
         # general association creation for both human users and app services
 
         for wchar in string.whitespace:
@@ -81,17 +88,21 @@ def _create_association(self, room_alias, room_id, servers=None, creator=None):
 
     @defer.inlineCallbacks
     def create_association(
-        self, requester, room_alias, room_id, servers=None, check_membership=True,
+        self,
+        requester: Requester,
+        room_alias: RoomAlias,
+        room_id: str,
+        servers: Optional[List[str]] = None,
+        check_membership: bool = True,
     ):
         """Attempt to create a new alias
 
         Args:
-            requester (Requester)
-            room_alias (RoomAlias)
-            room_id (str)
-            servers (list[str]|None): List of servers that others servers
-                should try and join via
-            check_membership (bool): Whether to check if the user is in the room
+            requester
+            room_alias
+            room_id
+            servers: Iterable of servers that others servers should try and join via
+            check_membership: Whether to check if the user is in the room
                 before the alias can be set (if the server's config requires it).
 
         Returns:
@@ -145,15 +156,15 @@ def create_association(
         yield self._create_association(room_alias, room_id, servers, creator=user_id)
 
     @defer.inlineCallbacks
-    def delete_association(self, requester, room_alias):
+    def delete_association(self, requester: Requester, room_alias: RoomAlias):
         """Remove an alias from the directory
 
         (this is only meant for human users; AS users should call
         delete_appservice_association)
 
         Args:
-            requester (Requester):
-            room_alias (RoomAlias):
+            requester
+            room_alias
 
         Returns:
             Deferred[unicode]: room id that the alias used to point to
@@ -189,16 +200,16 @@ def delete_association(self, requester, room_alias):
         room_id = yield self._delete_association(room_alias)
 
         try:
-            yield self._update_canonical_alias(
-                requester, requester.user.to_string(), room_id, room_alias
-            )
+            yield self._update_canonical_alias(requester, user_id, room_id, room_alias)
         except AuthError as e:
             logger.info("Failed to update alias events: %s", e)
 
         return room_id
 
     @defer.inlineCallbacks
-    def delete_appservice_association(self, service, room_alias):
+    def delete_appservice_association(
+        self, service: ApplicationService, room_alias: RoomAlias
+    ):
         if not service.is_interested_in_alias(room_alias.to_string()):
             raise SynapseError(
                 400,
@@ -208,7 +219,7 @@ def delete_appservice_association(self, service, room_alias):
         yield self._delete_association(room_alias)
 
     @defer.inlineCallbacks
-    def _delete_association(self, room_alias):
+    def _delete_association(self, room_alias: RoomAlias):
         if not self.hs.is_mine(room_alias):
             raise SynapseError(400, "Room alias must be local")
 
@@ -217,7 +228,7 @@ def _delete_association(self, room_alias):
         return room_id
 
     @defer.inlineCallbacks
-    def get_association(self, room_alias):
+    def get_association(self, room_alias: RoomAlias):
         room_id = None
         if self.hs.is_mine(room_alias):
             result = yield self.get_association_from_room_alias(room_alias)
@@ -282,7 +293,9 @@ def on_directory_query(self, args):
             )
 
     @defer.inlineCallbacks
-    def _update_canonical_alias(self, requester, user_id, room_id, room_alias):
+    def _update_canonical_alias(
+        self, requester: Requester, user_id: str, room_id: str, room_alias: RoomAlias
+    ):
         """
         Send an updated canonical alias event if the removed alias was set as
         the canonical alias or listed in the alt_aliases field.
@@ -331,15 +344,15 @@ def _update_canonical_alias(self, requester, user_id, room_id, room_alias):
             )
 
     @defer.inlineCallbacks
-    def get_association_from_room_alias(self, room_alias):
+    def get_association_from_room_alias(self, room_alias: RoomAlias):
         result = yield self.store.get_association_from_room_alias(room_alias)
         if not result:
             # Query AS to see if it exists
             as_handler = self.appservice_handler
             result = yield as_handler.query_room_alias_exists(room_alias)
         return result
 
-    def can_modify_alias(self, alias, user_id=None):
+    def can_modify_alias(self, alias: RoomAlias, user_id: Optional[str] = None):
         # Any application service "interested" in an alias they are regexing on
         # can modify the alias.
         # Users can only modify the alias if ALL the interested services have
@@ -360,22 +373,42 @@ def can_modify_alias(self, alias, user_id=None):
         return defer.succeed(True)
 
     @defer.inlineCallbacks
-    def _user_can_delete_alias(self, alias, user_id):
+    def _user_can_delete_alias(self, alias: RoomAlias, user_id: str):
+        """Determine whether a user can delete an alias.
+
+        One of the following must be true:
+
+        1. The user created the alias.
+        2. The user is a server administrator.
+        3. The user has a power-level sufficient to send a canonical alias event
+           for the current room.
+
+        """
         creator = yield self.store.get_room_alias_creator(alias.to_string())
 
         if creator is not None and creator == user_id:
             return True
 
-        is_admin = yield self.auth.is_server_admin(UserID.from_string(user_id))
-        return is_admin
+        # Resolve the alias to the corresponding room.
+        room_mapping = yield self.get_association(alias)
+        room_id = room_mapping["room_id"]
+        if not room_id:
+            return False
+
+        res = yield self.auth.check_can_change_room_list(
+            room_id, UserID.from_string(user_id)
+        )
+        return res
 
     @defer.inlineCallbacks
-    def edit_published_room_list(self, requester, room_id, visibility):
+    def edit_published_room_list(
+        self, requester: Requester, room_id: str, visibility: str
+    ):
         """Edit the entry of the room in the published room list.
 
         requester
-        room_id (str)
-        visibility (str): "public" or "private"
+        room_id
+        visibility: "public" or "private"
         """
         user_id = requester.user.to_string()
 
@@ -400,7 +433,15 @@ def edit_published_room_list(self, requester, room_id, visibility):
         if room is None:
             raise SynapseError(400, "Unknown room")
 
-        yield self.auth.check_can_change_room_list(room_id, requester.user)
+        can_change_room_list = yield self.auth.check_can_change_room_list(
+            room_id, requester.user
+        )
+        if not can_change_room_list:
+            raise AuthError(
+                403,
+                "This server requires you to be a moderator in the room to"
+                " edit its room list entry",
+            )
 
         making_public = visibility == "public"
         if making_public:
@@ -421,16 +462,16 @@ def edit_published_room_list(self, requester, room_id, visibility):
 
     @defer.inlineCallbacks
     def edit_published_appservice_room_list(
-        self, appservice_id, network_id, room_id, visibility
+        self, appservice_id: str, network_id: str, room_id: str, visibility: str
     ):
         """Add or remove a room from the appservice/network specific public
         room list.
 
         Args:
-            appservice_id (str): ID of the appservice that owns the list
-            network_id (str): The ID of the network the list is associated with
-            room_id (str)
-            visibility (str): either "public" or "private"
+            appservice_id: ID of the appservice that owns the list
+            network_id: The ID of the network the list is associated with
+            room_id
+            visibility: either "public" or "private"
         """
         if visibility not in ["public", "private"]:
             raise SynapseError(400, "Invalid visibility setting")