Allow third_party_signed to be specified on /join

2 files changed, 131 insertions, 29 deletions

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index ac15f9e5dd..3655b9e5e2 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -14,6 +14,9 @@
 # limitations under the License.
 
 """Contains handlers for federation events."""
+from signedjson.key import decode_verify_key_bytes
+from signedjson.sign import verify_signed_json
+from unpaddedbase64 import decode_base64
 
 from ._base import BaseHandler
 
@@ -1620,19 +1623,15 @@ class FederationHandler(BaseHandler):
 
     @defer.inlineCallbacks
     @log_function
-    def exchange_third_party_invite(self, invite):
-        sender = invite["sender"]
-        room_id = invite["room_id"]
-
-        if "signed" not in invite or "token" not in invite["signed"]:
-            logger.info(
-                "Discarding received notification of third party invite "
-                "without signed: %s" % (invite,)
-            )
-            return
-
+    def exchange_third_party_invite(
+            self,
+            sender_user_id,
+            target_user_id,
+            room_id,
+            signed,
+    ):
         third_party_invite = {
-            "signed": invite["signed"],
+            "signed": signed,
         }
 
         event_dict = {
@@ -1642,8 +1641,8 @@ class FederationHandler(BaseHandler):
                 "third_party_invite": third_party_invite,
             },
             "room_id": room_id,
-            "sender": sender,
-            "state_key": invite["mxid"],
+            "sender": sender_user_id,
+            "state_key": target_user_id,
         }
 
         if (yield self.auth.check_host_in_room(room_id, self.hs.hostname)):
@@ -1656,11 +1655,11 @@ class FederationHandler(BaseHandler):
             )
 
             self.auth.check(event, context.current_state)
-            yield self._validate_keyserver(event, auth_events=context.current_state)
+            yield self._check_signature(event, auth_events=context.current_state)
             member_handler = self.hs.get_handlers().room_member_handler
             yield member_handler.send_membership_event(event, context, from_client=False)
         else:
-            destinations = set([x.split(":", 1)[-1] for x in (sender, room_id)])
+            destinations = set(x.split(":", 1)[-1] for x in (sender_user_id, room_id))
             yield self.replication_layer.forward_third_party_invite(
                 destinations,
                 room_id,
@@ -1681,7 +1680,7 @@ class FederationHandler(BaseHandler):
         )
 
         self.auth.check(event, auth_events=context.current_state)
-        yield self._validate_keyserver(event, auth_events=context.current_state)
+        yield self._check_signature(event, auth_events=context.current_state)
 
         returned_invite = yield self.send_invite(origin, event)
         # TODO: Make sure the signatures actually are correct.
@@ -1711,17 +1710,69 @@ class FederationHandler(BaseHandler):
         defer.returnValue((event, context))
 
     @defer.inlineCallbacks
-    def _validate_keyserver(self, event, auth_events):
-        token = event.content["third_party_invite"]["signed"]["token"]
+    def _check_signature(self, event, auth_events):
+        """
+        Checks that the signature in the event is consistent with its invite.
+        :param event (Event): The m.room.member event to check
+        :param auth_events (dict<(event type, state_key), event>)
+
+        :raises
+            AuthError if signature didn't match any keys, or key has been
+                revoked,
+            SynapseError if a transient error meant a key couldn't be checked
+                for revocation.
+        """
+        signed = event.content["third_party_invite"]["signed"]
+        token = signed["token"]
 
         invite_event = auth_events.get(
             (EventTypes.ThirdPartyInvite, token,)
         )
 
+        if not invite_event:
+            raise AuthError(403, "Could not find invite")
+
+        last_exception = None
+        for public_key_object in self.hs.get_auth().get_public_keys(invite_event):
+            try:
+                for server, signature_block in signed["signatures"].items():
+                    for key_name, encoded_signature in signature_block.items():
+                        if not key_name.startswith("ed25519:"):
+                            continue
+
+                        public_key = public_key_object["public_key"]
+                        verify_key = decode_verify_key_bytes(
+                            key_name,
+                            decode_base64(public_key)
+                        )
+                        verify_signed_json(signed, server, verify_key)
+                        if "key_validity_url" in public_key_object:
+                            yield self._check_key_revocation(
+                                public_key,
+                                public_key_object["key_validity_url"]
+                            )
+                        return
+            except Exception as e:
+                last_exception = e
+        raise last_exception
+
+    @defer.inlineCallbacks
+    def _check_key_revocation(self, public_key, url):
+        """
+        Checks whether public_key has been revoked.
+
+        :param public_key (str): base-64 encoded public key.
+        :param url (str): Key revocation URL.
+
+        :raises
+            AuthError if they key has been revoked.
+            SynapseError if a transient error meant a key couldn't be checked
+                for revocation.
+        """
         try:
             response = yield self.hs.get_simple_http_client().get_json(
-                invite_event.content["key_validity_url"],
-                {"public_key": invite_event.content["public_key"]}
+                url,
+                {"public_key": public_key}
             )
         except Exception:
             raise SynapseError(
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index b00cac4bd4..eb9700a35b 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -398,6 +398,7 @@ class RoomMemberHandler(BaseHandler):
             action,
             txn_id=None,
             remote_room_hosts=None,
+            third_party_signed=None,
             ratelimit=True,
     ):
         effective_membership_state = action
@@ -406,6 +407,15 @@ class RoomMemberHandler(BaseHandler):
         elif action == "forget":
             effective_membership_state = "leave"
 
+        if third_party_signed is not None:
+            replication = self.hs.get_replication_layer()
+            yield replication.exchange_third_party_invite(
+                third_party_signed["sender"],
+                target.to_string(),
+                room_id,
+                third_party_signed,
+            )
+
         msg_handler = self.hs.get_handlers().message_handler
 
         content = {"membership": effective_membership_state}
@@ -759,7 +769,7 @@ class RoomMemberHandler(BaseHandler):
         if room_avatar_event:
             room_avatar_url = room_avatar_event.content.get("url", "")
 
-        token, public_key, key_validity_url, display_name = (
+        token, public_keys, fallback_public_key, display_name = (
             yield self._ask_id_server_for_third_party_invite(
                 id_server=id_server,
                 medium=medium,
@@ -774,14 +784,18 @@ class RoomMemberHandler(BaseHandler):
                 inviter_avatar_url=inviter_avatar_url
             )
         )
+
         msg_handler = self.hs.get_handlers().message_handler
         yield msg_handler.create_and_send_nonmember_event(
             {
                 "type": EventTypes.ThirdPartyInvite,
                 "content": {
                     "display_name": display_name,
-                    "key_validity_url": key_validity_url,
-                    "public_key": public_key,
+                    "public_keys": public_keys,
+
+                    # For backwards compatibility:
+                    "key_validity_url": fallback_public_key["key_validity_url"],
+                    "public_key": fallback_public_key["public_key"],
                 },
                 "room_id": room_id,
                 "sender": user.to_string(),
@@ -806,6 +820,34 @@ class RoomMemberHandler(BaseHandler):
             inviter_display_name,
             inviter_avatar_url
     ):
+        """
+        Asks an identity server for a third party invite.
+
+        :param id_server (str): hostname + optional port for the identity server.
+        :param medium (str): The literal string "email".
+        :param address (str): The third party address being invited.
+        :param room_id (str): The ID of the room to which the user is invited.
+        :param inviter_user_id (str): The user ID of the inviter.
+        :param room_alias (str): An alias for the room, for cosmetic
+            notifications.
+        :param room_avatar_url (str): The URL of the room's avatar, for cosmetic
+            notifications.
+        :param room_join_rules (str): The join rules of the email
+            (e.g. "public").
+        :param room_name (str): The m.room.name of the room.
+        :param inviter_display_name (str): The current display name of the
+            inviter.
+        :param inviter_avatar_url (str): The URL of the inviter's avatar.
+
+        :return: A deferred tuple containing:
+            token (str): The token which must be signed to prove authenticity.
+            public_keys ([{"public_key": str, "key_validity_url": str}]):
+                public_key is a base64-encoded ed25519 public key.
+            fallback_public_key: One element from public_keys.
+            display_name (str): A user-friendly name to represent the invited
+                user.
+        """
+
         is_url = "%s%s/_matrix/identity/api/v1/store-invite" % (
             id_server_scheme, id_server,
         )
@@ -826,12 +868,21 @@ class RoomMemberHandler(BaseHandler):
         )
         # TODO: Check for success
         token = data["token"]
-        public_key = data["public_key"]
+        public_keys = data.get("public_keys", [])
+        if "public_key" in data:
+            fallback_public_key = {
+                "public_key": data["public_key"],
+                "key_validity_url": "%s%s/_matrix/identity/api/v1/pubkey/isvalid" % (
+                    id_server_scheme, id_server,
+                ),
+            }
+        else:
+            fallback_public_key = public_keys[0]
+
+        if not public_keys:
+            public_keys.append(fallback_public_key)
         display_name = data["display_name"]
-        key_validity_url = "%s%s/_matrix/identity/api/v1/pubkey/isvalid" % (
-            id_server_scheme, id_server,
-        )
-        defer.returnValue((token, public_key, key_validity_url, display_name))
+        defer.returnValue((token, public_keys, fallback_public_key, display_name))
 
     def forget(self, user, room_id):
         return self.store.forget(user.to_string(), room_id)