Event auth allows booleans as power levels

[tulir]

Description

⁣Synapse validates power levels in event authorization using isinstance(v, int). However, booleans in Python are also instances of int. Therefore, Synapse allows booleans as power levels, even though v10 rooms should only allow ints.

Steps to reproduce

1. Disable the local (non-federation) event validation
2. Send a power level event in a v10 room that contains a boolean (true or false) where there should be an integer

Homeserver

maunium.net → matrix.org

Synapse Version

1.76.0rc2

Anything else that would be useful to know?

Power level event received and accepted by matrix.org:

{
  "content": {
    "events_default": false,
    "invite": true,
    "users": {
      "@tulir:matrix.org": true,
      "@tulir:maunium.net": 9001
    },
    "users_default": false
  },
  "origin_server_ts": 1675084843722,
  "sender": "@tulir:maunium.net",
  "state_key": "",
  "type": "m.room.power_levels",
  "unsigned": {
    "replaces_state": "$RevlilKC-G4vl1U--eXxjLKjEddGSr_zBFPGY-A7ftg"
  },
  "event_id": "$ij4iOVCAKqFzOijUqs4ZyuWRHpjkly5tYp8UR0NOQVU",
  "room_id": "!VielVjraKNGUibBfrN:maunium.net"
}