From 71f98a43a4c0224fa7fc4db653e84114e6998266 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Wed, 2 Mar 2022 07:49:20 -0500
Subject: [PATCH 1/2] Check if instances are lists, not sequences.

---
 synapse/federation/federation_client.py | 8 ++++----
 synapse/handlers/room_summary.py        | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 64e595e748f4..467275b98c3c 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -1428,7 +1428,7 @@ async def send_request(
 
             # Validate children_state of the room.
             children_state = room.pop("children_state", [])
-            if not isinstance(children_state, Sequence):
+            if not isinstance(children_state, list):
                 raise InvalidResponseError("'room.children_state' must be a list")
             if any(not isinstance(e, dict) for e in children_state):
                 raise InvalidResponseError("Invalid event in 'children_state' list")
@@ -1440,14 +1440,14 @@ async def send_request(
 
             # Validate the children rooms.
             children = res.get("children", [])
-            if not isinstance(children, Sequence):
+            if not isinstance(children, list):
                 raise InvalidResponseError("'children' must be a list")
             if any(not isinstance(r, dict) for r in children):
                 raise InvalidResponseError("Invalid room in 'children' list")
 
             # Validate the inaccessible children.
             inaccessible_children = res.get("inaccessible_children", [])
-            if not isinstance(inaccessible_children, Sequence):
+            if not isinstance(inaccessible_children, list):
                 raise InvalidResponseError("'inaccessible_children' must be a list")
             if any(not isinstance(r, str) for r in inaccessible_children):
                 raise InvalidResponseError(
@@ -1630,7 +1630,7 @@ def _validate_hierarchy_event(d: JsonDict) -> None:
         raise ValueError("Invalid event: 'content' must be a dict")
 
     via = content.get("via")
-    if not isinstance(via, Sequence):
+    if not isinstance(via, list):
         raise ValueError("Invalid event: 'via' must be a list")
     if any(not isinstance(v, str) for v in via):
         raise ValueError("Invalid event: 'via' must be a list of strings")
diff --git a/synapse/handlers/room_summary.py b/synapse/handlers/room_summary.py
index 55c2cbdba8bc..3979cbba71bd 100644
--- a/synapse/handlers/room_summary.py
+++ b/synapse/handlers/room_summary.py
@@ -857,7 +857,7 @@ def as_json(self) -> JsonDict:
 
 def _has_valid_via(e: EventBase) -> bool:
     via = e.content.get("via")
-    if not via or not isinstance(via, Sequence):
+    if not via or not isinstance(via, list):
         return False
     for v in via:
         if not isinstance(v, str):

From d921a793448bd4227390f02bfa9ce1b0273242ed Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Wed, 2 Mar 2022 07:50:56 -0500
Subject: [PATCH 2/2] Newsfragment

---
 changelog.d/12128.misc | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/12128.misc

diff --git a/changelog.d/12128.misc b/changelog.d/12128.misc
new file mode 100644
index 000000000000..0570a8e3272f
--- /dev/null
+++ b/changelog.d/12128.misc
@@ -0,0 +1 @@
+Fix data validation to compare to lists, not sequences.