Prevent federation user keys query from returning device names if disallowed (#14304)

1 files changed, 12 insertions, 5 deletions

diff --git a/synapse/storage/databases/main/end_to_end_keys.py b/synapse/storage/databases/main/end_to_end_keys.py
index 8a10ae800c..2a4f58ed92 100644
--- a/synapse/storage/databases/main/end_to_end_keys.py
+++ b/synapse/storage/databases/main/end_to_end_keys.py
@@ -139,11 +139,15 @@ class EndToEndKeyWorkerStore(EndToEndKeyBackgroundStore, CacheInvalidationWorker
     @trace
     @cancellable
     async def get_e2e_device_keys_for_cs_api(
-        self, query_list: List[Tuple[str, Optional[str]]]
+        self,
+        query_list: List[Tuple[str, Optional[str]]],
+        include_displaynames: bool = True,
     ) -> Dict[str, Dict[str, JsonDict]]:
         """Fetch a list of device keys, formatted suitably for the C/S API.
         Args:
-            query_list(list): List of pairs of user_ids and device_ids.
+            query_list: List of pairs of user_ids and device_ids.
+            include_displaynames: Whether to include the displayname of returned devices
+                (if one exists).
         Returns:
             Dict mapping from user-id to dict mapping from device_id to
             key data.  The key data will be a dict in the same format as the
@@ -166,9 +170,12 @@ class EndToEndKeyWorkerStore(EndToEndKeyBackgroundStore, CacheInvalidationWorker
                     continue
 
                 r["unsigned"] = {}
-                display_name = device_info.display_name
-                if display_name is not None:
-                    r["unsigned"]["device_display_name"] = display_name
+                if include_displaynames:
+                    # Include the device's display name in the "unsigned" dictionary
+                    display_name = device_info.display_name
+                    if display_name is not None:
+                        r["unsigned"]["device_display_name"] = display_name
+
                 rv[user_id][device_id] = r
 
         return rv