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

3 files changed, 46 insertions, 9 deletions

diff --git a/changelog.d/14304.bugfix b/changelog.d/14304.bugfix
new file mode 100644
index 0000000000..b8d4d91034
--- /dev/null
+++ b/changelog.d/14304.bugfix
@@ -0,0 +1 @@
+Fix a bug introduced in 1.34.0 where device names would be returned via a federation user key query request when `allow_device_name_lookup_over_federation` was set to `false`.
\ No newline at end of file
diff --git a/synapse/handlers/e2e_keys.py b/synapse/handlers/e2e_keys.py
index 09a2492afc..a9912c467d 100644
--- a/synapse/handlers/e2e_keys.py
+++ b/synapse/handlers/e2e_keys.py
@@ -49,6 +49,7 @@ logger = logging.getLogger(__name__)
 
 class E2eKeysHandler:
     def __init__(self, hs: "HomeServer"):
+        self.config = hs.config
         self.store = hs.get_datastores().main
         self.federation = hs.get_federation_client()
         self.device_handler = hs.get_device_handler()
@@ -431,13 +432,17 @@ class E2eKeysHandler:
     @trace
     @cancellable
     async def query_local_devices(
-        self, query: Mapping[str, Optional[List[str]]]
+        self,
+        query: Mapping[str, Optional[List[str]]],
+        include_displaynames: bool = True,
     ) -> Dict[str, Dict[str, dict]]:
         """Get E2E device keys for local users
 
         Args:
             query: map from user_id to a list
                  of devices to query (None for all devices)
+            include_displaynames: Whether to include device displaynames in the returned
+                device details.
 
         Returns:
             A map from user_id -> device_id -> device details
@@ -469,7 +474,9 @@ class E2eKeysHandler:
             # make sure that each queried user appears in the result dict
             result_dict[user_id] = {}
 
-        results = await self.store.get_e2e_device_keys_for_cs_api(local_query)
+        results = await self.store.get_e2e_device_keys_for_cs_api(
+            local_query, include_displaynames
+        )
 
         # Build the result structure
         for user_id, device_keys in results.items():
@@ -482,11 +489,33 @@ class E2eKeysHandler:
     async def on_federation_query_client_keys(
         self, query_body: Dict[str, Dict[str, Optional[List[str]]]]
     ) -> JsonDict:
-        """Handle a device key query from a federated server"""
+        """Handle a device key query from a federated server:
+
+        Handles the path: GET /_matrix/federation/v1/users/keys/query
+
+        Args:
+            query_body: The body of the query request. Should contain a key
+                "device_keys" that map to a dictionary of user ID's -> list of
+                device IDs. If the list of device IDs is empty, all devices of
+                that user will be queried.
+
+        Returns:
+            A json dictionary containing the following:
+                - device_keys: A dictionary containing the requested device information.
+                - master_keys: An optional dictionary of user ID -> master cross-signing
+                   key info.
+                - self_signing_key: An optional dictionary of user ID -> self-signing
+                    key info.
+        """
         device_keys_query: Dict[str, Optional[List[str]]] = query_body.get(
             "device_keys", {}
         )
-        res = await self.query_local_devices(device_keys_query)
+        res = await self.query_local_devices(
+            device_keys_query,
+            include_displaynames=(
+                self.config.federation.allow_device_name_lookup_over_federation
+            ),
+        )
         ret = {"device_keys": res}
 
         # add in the cross-signing keys
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