Configurable limits on avatars (#11846)

Only allow files which file size and content types match configured
limits to be set as avatar.

Most of the inspiration from the non-test code comes from matrix-org/synapse-dinsic#19

synapse/config/server.py

@@ -489,6 +489,19 @@ class ServerConfig(Config):
         # events with profile information that differ from the target's global profile.
         self.allow_per_room_profiles = config.get("allow_per_room_profiles", True)
 
+        # The maximum size an avatar can have, in bytes.
+        self.max_avatar_size = config.get("max_avatar_size")
+        if self.max_avatar_size is not None:
+            self.max_avatar_size = self.parse_size(self.max_avatar_size)
+
+        # The MIME types allowed for an avatar.
+        self.allowed_avatar_mimetypes = config.get("allowed_avatar_mimetypes")
+        if self.allowed_avatar_mimetypes and not isinstance(
+            self.allowed_avatar_mimetypes,
+            list,
+        ):
+            raise ConfigError("allowed_avatar_mimetypes must be a list")
+
         self.listeners = [parse_listener_def(x) for x in config.get("listeners", [])]
 
         # no_tls is not really supported any more, but let's grandfather it in
@@ -1168,6 +1181,20 @@ class ServerConfig(Config):
         #
         #allow_per_room_profiles: false
 
+        # The largest allowed file size for a user avatar. Defaults to no restriction.
+        #
+        # Note that user avatar changes will not work if this is set without
+        # using Synapse's media repository.
+        #
+        #max_avatar_size: 10M
+
+        # The MIME types allowed for user avatars. Defaults to no restriction.
+        #
+        # Note that user avatar changes will not work if this is set without
+        # using Synapse's media repository.
+        #
+        #allowed_avatar_mimetypes: ["image/png", "image/jpeg", "image/gif"]
+
         # How long to keep redacted events in unredacted form in the database. After
         # this period redacted events get replaced with their redacted form in the DB.
         #