Validate alt_aliases property of canonical alias events

changelog.d/6971.feature

@@ -0,0 +1 @@
+Validate the alt_aliases property of canonical alias events.

synapse/api/errors.py

@@ -66,6 +66,7 @@ class Codes(object):
     EXPIRED_ACCOUNT = "ORG_MATRIX_EXPIRED_ACCOUNT"
     INVALID_SIGNATURE = "M_INVALID_SIGNATURE"
     USER_DEACTIVATED = "M_USER_DEACTIVATED"
+    BAD_ALIAS = "M_BAD_ALIAS"
 
 
 class CodeMessageException(RuntimeError):

synapse/handlers/directory.py

@@ -13,8 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-
-import collections
 import logging
 import string
 from typing import List
@@ -307,15 +305,17 @@ def _update_canonical_alias(self, requester, user_id, room_id, room_alias):
             send_update = True
             content.pop("alias", "")
 
-        # Filter alt_aliases for the removed alias.
-        alt_aliases = content.pop("alt_aliases", None)
-        # If the aliases are not a list (or not found) do not attempt to modify
-        # the list.
-        if isinstance(alt_aliases, collections.Sequence):
+        # Filter the alt_aliases property for the removed alias. Note that the
+        # value is not modified if alt_aliases is of an unexpected form.
+        alt_aliases = content.get("alt_aliases")
+        if isinstance(alt_aliases, (list, tuple)) and alias_str in alt_aliases:
             send_update = True
             alt_aliases = [alias for alias in alt_aliases if alias != alias_str]
+
             if alt_aliases:
                 content["alt_aliases"] = alt_aliases
+            else:
+                del content["alt_aliases"]
 
         if send_update:
             yield self.event_creation_handler.create_and_send_nonmember_event(

synapse/handlers/message.py

@@ -888,19 +888,60 @@ def persist_and_notify_client_event(
         yield self.base_handler.maybe_kick_guest_users(event, context)
 
         if event.type == EventTypes.CanonicalAlias:
-            # Check the alias is acually valid (at this time at least)
+            # Validate a newly added alias or newly added alt_aliases.
+
+            original_alias = None
+            original_alt_aliases = set()
+
+            original_event_id = event.unsigned.get("replaces_state")
+            if original_event_id:
+                original_event = yield self.store.get_event(original_event_id)
+
+                if original_event:
+                    original_alias = original_event.content.get("alias", None)
+                    original_alt_aliases = original_event.content.get("alt_aliases", [])
+
+            # Check the alias is currently valid (if it has changed).
             room_alias_str = event.content.get("alias", None)
-            if room_alias_str:
+            directory_handler = self.hs.get_handlers().directory_handler
+            if room_alias_str and room_alias_str != original_alias:
                 room_alias = RoomAlias.from_string(room_alias_str)
-                directory_handler = self.hs.get_handlers().directory_handler
                 mapping = yield directory_handler.get_association(room_alias)
 
                 if mapping["room_id"] != event.room_id:
                     raise SynapseError(
                         400,
                         "Room alias %s does not point to the room" % (room_alias_str,),
+                        Codes.BAD_ALIAS,
                     )
 
+            # Check that alt_aliases is the proper form.
+            alt_aliases = event.content.get("alt_aliases", [])
+            if not isinstance(alt_aliases, (list, tuple)):
+                raise SynapseError(
+                    400, "The alt_aliases property must be a list.", Codes.INVALID_PARAM
+                )
+
+            # If the old version of alt_aliases is of an unknown form,
+            # completely replace it.
+            if not isinstance(original_alt_aliases, (list, tuple)):
+                original_alt_aliases = []
+
+            # Check that each alias is currently valid.
+            new_alt_aliases = set(alt_aliases) - set(original_alt_aliases)
+            if new_alt_aliases:
+                for alias_str in new_alt_aliases:
+                    room_alias = RoomAlias.from_string(alias_str)
+                    mapping = yield directory_handler.get_association(room_alias)
+
+                    if mapping["room_id"] != event.room_id:
+                        raise SynapseError(
+                            400,
+                            "Room alias %s does not point to the room"
+                            % (room_alias_str,),
+                            Codes.BAD_ALIAS,
+                        )
+
         federation_handler = self.hs.get_handlers().federation_handler
 
         if event.type == EventTypes.Member:

synapse/types.py

@@ -23,7 +23,7 @@
 from signedjson.key import decode_verify_key_bytes
 from unpaddedbase64 import decode_base64
 
-from synapse.api.errors import SynapseError
+from synapse.api.errors import Codes, SynapseError
 
 # define a version of typing.Collection that works on python 3.5
 if sys.version_info[:3] >= (3, 6, 0):
@@ -166,11 +166,13 @@ def __deepcopy__(self, memo):
         return self
 
     @classmethod
-    def from_string(cls, s):
+    def from_string(cls, s: str):
         """Parse the string given by 's' into a structure object."""
         if len(s) < 1 or s[0:1] != cls.SIGIL:
             raise SynapseError(
-                400, "Expected %s string to start with '%s'" % (cls.__name__, cls.SIGIL)
+                400,
+                "Expected %s string to start with '%s'" % (cls.__name__, cls.SIGIL),
+                Codes.INVALID_PARAM,
             )
 
         parts = s[1:].split(":", 1)
@@ -179,6 +181,7 @@ def from_string(cls, s):
                 400,
                 "Expected %s of the form '%slocalname:domain'"
                 % (cls.__name__, cls.SIGIL),
+                Codes.INVALID_PARAM,
             )
 
         domain = parts[1]
@@ -235,11 +238,13 @@ class GroupID(DomainSpecificString):
     def from_string(cls, s):
         group_id = super(GroupID, cls).from_string(s)
         if not group_id.localpart:
-            raise SynapseError(400, "Group ID cannot be empty")
+            raise SynapseError(400, "Group ID cannot be empty", Codes.INVALID_PARAM)
 
         if contains_invalid_mxid_characters(group_id.localpart):
             raise SynapseError(
-                400, "Group ID can only contain characters a-z, 0-9, or '=_-./'"
+                400,
+                "Group ID can only contain characters a-z, 0-9, or '=_-./'",
+                Codes.INVALID_PARAM,
             )
 
         return group_id

tests/handlers/test_directory.py

@@ -88,6 +88,7 @@ def test_get_remote_association(self):
         )
 
     def test_delete_alias_not_allowed(self):
+        """Removing an alias should be denied if a user does not have the proper permissions."""
         room_id = "!8765qwer:test"
         self.get_success(
             self.store.create_room_alias_association(self.my_room, room_id, ["test"])
@@ -101,6 +102,7 @@ def test_delete_alias_not_allowed(self):
         )
 
     def test_delete_alias(self):
+        """Removing an alias should work when a user does has the proper permissions."""
         room_id = "!8765qwer:test"
         user_id = "@user:test"
         self.get_success(
@@ -159,30 +161,42 @@ def prepare(self, reactor, clock, hs):
         )
 
         self.test_alias = "#test:test"
-        self.room_alias = RoomAlias.from_string(self.test_alias)
+        self.room_alias = self._add_alias(self.test_alias)
+
+    def _add_alias(self, alias: str) -> RoomAlias:
+        """Add an alias to the test room."""
+        room_alias = RoomAlias.from_string(alias)
 
         # Create a new alias to this room.
         self.get_success(
             self.store.create_room_alias_association(
-                self.room_alias, self.room_id, ["test"], self.admin_user
+                room_alias, self.room_id, ["test"], self.admin_user
             )
         )
+        return room_alias
 
-    def test_remove_alias(self):
-        """Removing an alias that is the canonical alias should remove it there too."""
-        # Set this new alias as the canonical alias for this room
+    def _set_canonical_alias(self, content):
+        """Configure the canonical alias state on the room."""
         self.helper.send_state(
-            self.room_id,
-            "m.room.canonical_alias",
-            {"alias": self.test_alias, "alt_aliases": [self.test_alias]},
-            tok=self.admin_user_tok,
+            self.room_id, "m.room.canonical_alias", content, tok=self.admin_user_tok,
         )
 
-        data = self.get_success(
+    def _get_canonical_alias(self):
+        """Get the canonical alias state of the room."""
+        return self.get_success(
             self.state_handler.get_current_state(
                 self.room_id, EventTypes.CanonicalAlias, ""
             )
         )
+
+    def test_remove_alias(self):
+        """Removing an alias that is the canonical alias should remove it there too."""
+        # Set this new alias as the canonical alias for this room
+        self._set_canonical_alias(
+            {"alias": self.test_alias, "alt_aliases": [self.test_alias]}
+        )
+
+        data = self._get_canonical_alias()
         self.assertEqual(data["content"]["alias"], self.test_alias)
         self.assertEqual(data["content"]["alt_aliases"], [self.test_alias])
 
@@ -193,41 +207,25 @@ def test_remove_alias(self):
             )
         )
 
-        data = self.get_success(
-            self.state_handler.get_current_state(
-                self.room_id, EventTypes.CanonicalAlias, ""
-            )
-        )
+        data = self._get_canonical_alias()
         self.assertNotIn("alias", data["content"])
         self.assertNotIn("alt_aliases", data["content"])
 
     def test_remove_other_alias(self):
         """Removing an alias listed as in alt_aliases should remove it there too."""
         # Create a second alias.
         other_test_alias = "#test2:test"
-        other_room_alias = RoomAlias.from_string(other_test_alias)
-        self.get_success(
-            self.store.create_room_alias_association(
-                other_room_alias, self.room_id, ["test"], self.admin_user
-            )
-        )
+        other_room_alias = self._add_alias(other_test_alias)
 
         # Set the alias as the canonical alias for this room.
-        self.helper.send_state(
-            self.room_id,
-            "m.room.canonical_alias",
+        self._set_canonical_alias(
             {
                 "alias": self.test_alias,
                 "alt_aliases": [self.test_alias, other_test_alias],
-            },
-            tok=self.admin_user_tok,
+            }
         )
 
-        data = self.get_success(
-            self.state_handler.get_current_state(
-                self.room_id, EventTypes.CanonicalAlias, ""
-            )
-        )
+        data = self._get_canonical_alias()
         self.assertEqual(data["content"]["alias"], self.test_alias)
         self.assertEqual(
             data["content"]["alt_aliases"], [self.test_alias, other_test_alias]
@@ -240,11 +238,7 @@ def test_remove_other_alias(self):
             )
         )
 
-        data = self.get_success(
-            self.state_handler.get_current_state(
-                self.room_id, EventTypes.CanonicalAlias, ""
-            )
-        )
+        data = self._get_canonical_alias()
         self.assertEqual(data["content"]["alias"], self.test_alias)
         self.assertEqual(data["content"]["alt_aliases"], [self.test_alias])