blindly incorporate PR review - needs testing & fixing

synapse/api/errors.py

@@ -289,9 +289,14 @@ class LimitExceededError(SynapseError):
 class RoomKeysVersionError(SynapseError):
     """A client has tried to upload to a non-current version of the room_keys store
     """
-    def __init__(self, code=403, msg="Wrong room_keys version", current_version=None,
+    def __init__(self, current_version):
-                 errcode=Codes.WRONG_ROOM_KEYS_VERSION):
+        """
-        super(RoomKeysVersionError, self).__init__(code, msg, errcode)
+        Args:
+            current_version (str): the current version of the store they should have used
+        """
+        super(RoomKeysVersionError, self).__init__(
+            403, "Wrong room_keys version", Codes.WRONG_ROOM_KEYS_VERSION
+        )
         self.current_version = current_version
 
     def error_dict(self):

synapse/handlers/e2e_room_keys.py

@@ -24,8 +24,21 @@ logger = logging.getLogger(__name__)
 
 
 class E2eRoomKeysHandler(object):
+    """
+    Implements an optional realtime backup mechanism for encrypted E2E megolm room keys.
+    This gives a way for users to store and recover their megolm keys if they lose all
+    their clients. It should also extend easily to future room key mechanisms.
+    The actual payload of the encrypted keys is completely opaque to the handler.
+    """
+
     def __init__(self, hs):
         self.store = hs.get_datastore()
+
+        # Used to lock whenever a client is uploading key data.  This prevents collisions
+        # between clients trying to upload the details of a new session, given all
+        # clients belonging to a user will receive and try to upload a new session at
+        # roughly the same time.  Also used to lock out uploads when the key is being
+        # changed.
         self._upload_linearizer = Linearizer("upload_room_keys_lock")
 
     @defer.inlineCallbacks
@@ -40,6 +53,8 @@ class E2eRoomKeysHandler(object):
 
     @defer.inlineCallbacks
     def delete_room_keys(self, user_id, version, room_id, session_id):
+        # lock for consistency with uploading
+        with (yield self._upload_linearizer.queue(user_id)):
             yield self.store.delete_e2e_room_keys(user_id, version, room_id, session_id)
 
     @defer.inlineCallbacks
@@ -47,8 +62,9 @@ class E2eRoomKeysHandler(object):
 
         # TODO: Validate the JSON to make sure it has the right keys.
 
+        # XXX: perhaps we should use a finer grained lock here?
+        with (yield self._upload_linearizer.queue(user_id)):
             # Check that the version we're trying to upload is the current version
-
             try:
                 version_info = yield self.get_version_info(user_id, version)
             except StoreError as e:
@@ -60,13 +76,11 @@ class E2eRoomKeysHandler(object):
             if version_info['version'] != version:
                 raise RoomKeysVersionError(current_version=version_info.version)
 
-        # XXX: perhaps we should use a finer grained lock here?
+            # go through the room_keys.
-        with (yield self._upload_linearizer.queue(user_id)):
+            # XXX: this should/could be done concurrently, given we're in a lock.
-
+            for room_id, room in room_keys['rooms'].iteritems():
-            # go through the room_keys
+                for session_id, session in room['sessions'].iteritems():
-            for room_id in room_keys['rooms']:
+                    room_key = session[session_id]
-                for session_id in room_keys['rooms'][room_id]['sessions']:
-                    room_key = room_keys['rooms'][room_id]['sessions'][session_id]
 
                     yield self._upload_room_key(
                         user_id, version, room_id, session_id, room_key
@@ -86,10 +100,29 @@ class E2eRoomKeysHandler(object):
             else:
                 raise e
 
-        # check whether we merge or not. spelling it out with if/elifs rather
+        if _should_replace_room_key(current_room_key, room_key):
-        # than lots of booleans for legibility.
+            yield self.store.set_e2e_room_key(
-        upsert = True
+                user_id, version, room_id, session_id, room_key
+            )
+
+    def _should_replace_room_key(current_room_key, room_key):
+        """
+        Determine whether to replace the current_room_key in our backup for this
+        session (if any) with a new room_key that has been uploaded.
+
+        Args:
+            current_room_key (dict): Optional, the current room_key dict if any
+            room_key (dict): The new room_key dict which may or may not be fit to
+                replace the current_room_key
+
+        Returns:
+            True if current_room_key should be replaced by room_key in the backup
+        """
+
         if current_room_key:
+            # spelt out with if/elifs rather than nested boolean expressions
+            # purely for legibility.
+
             if room_key['is_verified'] and not current_room_key['is_verified']:
                 pass
             elif (
@@ -97,16 +130,11 @@ class E2eRoomKeysHandler(object):
                 current_room_key['first_message_index']
             ):
                 pass
-            elif room_key['forwarded_count'] < room_key['forwarded_count']:
+            elif room_key['forwarded_count'] < current_room_key['forwarded_count']:
                 pass
             else:
-                upsert = False
+                return False
-
+        return True
-        # if so, we set the new room_key
-        if upsert:
-            yield self.store.set_e2e_room_key(
-                user_id, version, room_id, session_id, room_key
-            )
 
     @defer.inlineCallbacks
     def create_version(self, user_id, version_info):

synapse/rest/client/v2_alpha/room_keys.py

@@ -68,6 +68,8 @@ class RoomKeysServlet(RestServlet):
          * lower forwarded_count always wins over higher forwarded_count
 
         We trust the clients not to lie and corrupt their own backups.
+        It also means that if your access_token is stolen, the attacker could
+        delete your backup.
 
         POST /room_keys/keys/!abc:matrix.org/c0ff33?version=1 HTTP/1.1
         Content-Type: application/json

synapse/storage/e2e_room_keys.py

@@ -44,10 +44,7 @@ class EndToEndRoomKeyStore(SQLBaseStore):
 
     def set_e2e_room_key(self, user_id, version, room_id, session_id, room_key):
 
-        def _set_e2e_room_key_txn(txn):
+        yield self._simple_upsert(
-
-            self._simple_upsert_txn(
-                txn,
             table="e2e_room_keys",
             keyvalues={
                 "user_id": user_id,
@@ -64,12 +61,6 @@ class EndToEndRoomKeyStore(SQLBaseStore):
             lock=False,
         )
 
-            return True
-
-        return self.runInteraction(
-            "set_e2e_room_key", _set_e2e_room_key_txn
-        )
-
     # XXX: this isn't currently used and isn't tested anywhere
     # it could be used in future for bulk-uploading new versions of room_keys
     # for a user or something though.
@@ -107,7 +98,9 @@ class EndToEndRoomKeyStore(SQLBaseStore):
         )
 
     @defer.inlineCallbacks
-    def get_e2e_room_keys(self, user_id, version, room_id, session_id):
+    def get_e2e_room_keys(
+        self, user_id, version, room_id=room_id, session_id=session_id
+    ):
 
         keyvalues = {
             "user_id": user_id,
@@ -133,18 +126,10 @@ class EndToEndRoomKeyStore(SQLBaseStore):
             desc="get_e2e_room_keys",
         )
 
-        # perlesque autovivification from https://stackoverflow.com/a/19829714/6764493
+        sessions = {}
-        class AutoVivification(dict):
-            def __getitem__(self, item):
-                try:
-                    return dict.__getitem__(self, item)
-                except KeyError:
-                    value = self[item] = type(self)()
-                    return value
-
-        sessions = AutoVivification()
         for row in rows:
-            sessions['rooms'][row['room_id']]['sessions'][row['session_id']] = {
+            room_entry = sessions['rooms'].setdefault(row['room_id'], {"sessions": {}})
+            room_entry['sessions'][row['session_id']] = {
                 "first_message_index": row["first_message_index"],
                 "forwarded_count": row["forwarded_count"],
                 "is_verified": row["is_verified"],
@@ -154,7 +139,9 @@ class EndToEndRoomKeyStore(SQLBaseStore):
         defer.returnValue(sessions)
 
     @defer.inlineCallbacks
-    def delete_e2e_room_keys(self, user_id, version, room_id, session_id):
+    def delete_e2e_room_keys(
+        self, user_id, version, room_id=room_id, session_id=session_id
+    ):
 
         keyvalues = {
             "user_id": user_id,

synapse/storage/schema/delta/46/e2e_room_keys.sql

@@ -25,16 +25,14 @@ CREATE TABLE e2e_room_keys (
     session_data TEXT NOT NULL
 );
 
-CREATE UNIQUE INDEX e2e_room_keys_user_idx ON e2e_room_keys(user_id);
+CREATE UNIQUE INDEX e2e_room_keys_idx ON e2e_room_keys(user_id, room_id, session_id);
-CREATE UNIQUE INDEX e2e_room_keys_room_idx ON e2e_room_keys(room_id);
-CREATE UNIQUE INDEX e2e_room_keys_session_idx ON e2e_room_keys(session_id);
 
 -- the metadata for each generation of encrypted e2e session backups
-CREATE TABLE e2e_room_key_versions (
+CREATE TABLE e2e_room_keys_versions (
     user_id TEXT NOT NULL,
     version TEXT NOT NULL,
     algorithm TEXT NOT NULL,
     auth_data TEXT NOT NULL
 );
 
-CREATE UNIQUE INDEX e2e_room_key_user_idx ON e2e_room_keys(user_id);
+CREATE UNIQUE INDEX e2e_room_keys_versions_user_idx ON e2e_room_keys_versions(user_id);