Add federation_domain_whitelist option (#2820)

Add federation_domain_whitelist

gives a way to restrict which domains your HS is allowed to federate with.
useful mainly for gracefully preventing a private but internet-connected HS from trying to federate to the wider public Matrix network

4 files changed, 18 insertions, 3 deletions

diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index b1fe03f702..813907f7f2 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -23,7 +23,7 @@ from twisted.internet import defer
 
 from synapse.api.constants import Membership
 from synapse.api.errors import (
-    CodeMessageException, HttpResponseException, SynapseError,
+    CodeMessageException, HttpResponseException, SynapseError, FederationDeniedError
 )
 from synapse.events import builder
 from synapse.federation.federation_base import (
@@ -266,6 +266,9 @@ class FederationClient(FederationBase):
             except NotRetryingDestination as e:
                 logger.info(e.message)
                 continue
+            except FederationDeniedError as e:
+                logger.info(e.message)
+                continue
             except Exception as e:
                 pdu_attempts[destination] = now
 
diff --git a/synapse/federation/transaction_queue.py b/synapse/federation/transaction_queue.py
index 9d39f46583..a141ec9953 100644
--- a/synapse/federation/transaction_queue.py
+++ b/synapse/federation/transaction_queue.py
@@ -19,7 +19,7 @@ from twisted.internet import defer
 from .persistence import TransactionActions
 from .units import Transaction, Edu
 
-from synapse.api.errors import HttpResponseException
+from synapse.api.errors import HttpResponseException, FederationDeniedError
 from synapse.util import logcontext, PreserveLoggingContext
 from synapse.util.async import run_on_reactor
 from synapse.util.retryutils import NotRetryingDestination, get_retry_limiter
@@ -490,6 +490,8 @@ class TransactionQueue(object):
                     (e.retry_last_ts + e.retry_interval) / 1000.0
                 ),
             )
+        except FederationDeniedError as e:
+            logger.info(e)
         except Exception as e:
             logger.warn(
                 "TX [%s] Failed to send transaction: %s",
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 1f3ce238f6..5488e82985 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -212,6 +212,9 @@ class TransportLayerClient(object):
 
             Fails with ``NotRetryingDestination`` if we are not yet ready
             to retry this server.
+
+            Fails with ``FederationDeniedError`` if the remote destination
+            is not in our federation whitelist
         """
         valid_memberships = {Membership.JOIN, Membership.LEAVE}
         if membership not in valid_memberships:
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index 2b02b021ec..06c16ba4fa 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -16,7 +16,7 @@
 from twisted.internet import defer
 
 from synapse.api.urls import FEDERATION_PREFIX as PREFIX
-from synapse.api.errors import Codes, SynapseError
+from synapse.api.errors import Codes, SynapseError, FederationDeniedError
 from synapse.http.server import JsonResource
 from synapse.http.servlet import (
     parse_json_object_from_request, parse_integer_from_args, parse_string_from_args,
@@ -81,6 +81,7 @@ class Authenticator(object):
         self.keyring = hs.get_keyring()
         self.server_name = hs.hostname
         self.store = hs.get_datastore()
+        self.federation_domain_whitelist = hs.config.federation_domain_whitelist
 
     # A method just so we can pass 'self' as the authenticator to the Servlets
     @defer.inlineCallbacks
@@ -92,6 +93,12 @@ class Authenticator(object):
             "signatures": {},
         }
 
+        if (
+            self.federation_domain_whitelist is not None and
+            self.server_name not in self.federation_domain_whitelist
+        ):
+            raise FederationDeniedError(self.server_name)
+
         if content is not None:
             json_request["content"] = content