Do checks on aliases for incoming m.room.aliases events (#5128)

Follow-up to #5124

Also added a bunch of checks to make sure everything (both the stuff added on #5124 and this PR) works as intended.

2 files changed, 19 insertions, 4 deletions

diff --git a/synapse/events/snapshot.py b/synapse/events/snapshot.py
index 368b5f6ae4..fa09c132a0 100644
--- a/synapse/events/snapshot.py
+++ b/synapse/events/snapshot.py
@@ -187,7 +187,9 @@ class EventContext(object):
 
         Returns:
             Deferred[dict[(str, str), str]|None]: Returns None if state_group
-            is None, which happens when the associated event is an outlier.
+                is None, which happens when the associated event is an outlier.
+                Maps a (type, state_key) to the event ID of the state event matching
+                this tuple.
         """
 
         if not self._fetching_state_deferred:
@@ -205,7 +207,9 @@ class EventContext(object):
 
         Returns:
             Deferred[dict[(str, str), str]|None]: Returns None if state_group
-            is None, which happens when the associated event is an outlier.
+                is None, which happens when the associated event is an outlier.
+                Maps a (type, state_key) to the event ID of the state event matching
+                this tuple.
         """
 
         if not self._fetching_state_deferred:
diff --git a/synapse/events/validator.py b/synapse/events/validator.py
index 514273c792..711af512b2 100644
--- a/synapse/events/validator.py
+++ b/synapse/events/validator.py
@@ -15,8 +15,8 @@
 
 from six import string_types
 
-from synapse.api.constants import EventTypes, Membership
-from synapse.api.errors import SynapseError
+from synapse.api.constants import MAX_ALIAS_LENGTH, EventTypes, Membership
+from synapse.api.errors import Codes, SynapseError
 from synapse.api.room_versions import EventFormatVersions
 from synapse.types import EventID, RoomID, UserID
 
@@ -56,6 +56,17 @@ class EventValidator(object):
             if not isinstance(getattr(event, s), string_types):
                 raise SynapseError(400, "'%s' not a string type" % (s,))
 
+        if event.type == EventTypes.Aliases:
+            if "aliases" in event.content:
+                for alias in event.content["aliases"]:
+                    if len(alias) > MAX_ALIAS_LENGTH:
+                        raise SynapseError(
+                            400,
+                            ("Can't create aliases longer than"
+                             " %d characters" % (MAX_ALIAS_LENGTH,)),
+                            Codes.INVALID_PARAM,
+                        )
+
     def validate_builder(self, event):
         """Validates that the builder/event has roughly the right format. Only
         checks values that we expect a proto event to have, rather than all the