Reject attempts to send event before privacy consent is given

Returns an M_CONSENT_NOT_GIVEN error (cf
https://github.com/matrix-org/matrix-doc/issues/1252) if consent is not yet
given.

synapse/api/errors.py

@@ -19,6 +19,7 @@
 
 import simplejson as json
 from six import iteritems
+from six.moves import http_client
 
 logger = logging.getLogger(__name__)
 
@@ -51,6 +52,7 @@ class Codes(object):
     THREEPID_DENIED = "M_THREEPID_DENIED"
     INVALID_USERNAME = "M_INVALID_USERNAME"
     SERVER_NOT_TRUSTED = "M_SERVER_NOT_TRUSTED"
+    CONSENT_NOT_GIVEN = "M_CONSENT_NOT_GIVEN"
 
 
 class CodeMessageException(RuntimeError):
@@ -138,6 +140,32 @@ def from_http_response_exception(cls, err):
         return res
 
 
+class ConsentNotGivenError(SynapseError):
+    """The error returned to the client when the user has not consented to the
+    privacy policy.
+    """
+    def __init__(self, msg, consent_uri):
+        """Constructs a ConsentNotGivenError
+
+        Args:
+            msg (str): The human-readable error message
+            consent_url (str): The URL where the user can give their consent
+        """
+        super(ConsentNotGivenError, self).__init__(
+            code=http_client.FORBIDDEN,
+            msg=msg,
+            errcode=Codes.CONSENT_NOT_GIVEN
+        )
+        self._consent_uri = consent_uri
+
+    def error_dict(self):
+        return cs_error(
+            self.msg,
+            self.errcode,
+            consent_uri=self._consent_uri
+        )
+
+
 class RegistrationError(SynapseError):
     """An error raised when a registration event fails."""
     pass
@@ -292,7 +320,7 @@ def cs_error(msg, code=Codes.UNKNOWN, **kwargs):
 
     Args:
         msg (str): The error message.
-        code (int): The error code.
+        code (str): The error code.
         kwargs : Additional keys to add to the response.
     Returns:
         A dict representing the error response JSON.

synapse/api/urls.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 # Copyright 2014-2016 OpenMarket Ltd
+# Copyright 2018 New Vector Ltd.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -14,6 +15,12 @@
 # limitations under the License.
 
 """Contains the URL paths to prefix various aspects of the server with. """
+from hashlib import sha256
+import hmac
+
+from six.moves.urllib.parse import urlencode
+
+from synapse.config import ConfigError
 
 CLIENT_PREFIX = "/_matrix/client/api/v1"
 CLIENT_V2_ALPHA_PREFIX = "/_matrix/client/v2_alpha"
@@ -25,3 +32,46 @@
 SERVER_KEY_V2_PREFIX = "/_matrix/key/v2"
 MEDIA_PREFIX = "/_matrix/media/r0"
 LEGACY_MEDIA_PREFIX = "/_matrix/media/v1"
+
+
+class ConsentURIBuilder(object):
+    def __init__(self, hs_config):
+        """
+        Args:
+            hs_config (synapse.config.homeserver.HomeServerConfig):
+        """
+        if hs_config.form_secret is None:
+            raise ConfigError(
+                "form_secret not set in config",
+            )
+        if hs_config.public_baseurl is None:
+            raise ConfigError(
+                "public_baseurl not set in config",
+            )
+
+        self._hmac_secret = hs_config.form_secret.encode("utf-8")
+        self._public_baseurl = hs_config.public_baseurl
+
+    def build_user_consent_uri(self, user_id):
+        """Build a URI which we can give to the user to do their privacy
+        policy consent
+
+        Args:
+            user_id (str): mxid or username of user
+
+        Returns
+            (str) the URI where the user can do consent
+        """
+        mac = hmac.new(
+            key=self._hmac_secret,
+            msg=user_id,
+            digestmod=sha256,
+        ).hexdigest()
+        consent_uri = "%s_matrix/consent?%s" % (
+            self._public_baseurl,
+            urlencode({
+                "u": user_id,
+                "h": mac
+            }),
+        )
+        return consent_uri

synapse/config/consent_config.py

@@ -34,13 +34,19 @@
 # asking them to consent to the privacy policy. The 'server_notices' section
 # must also be configured for this to work.
 #
+# 'block_events_error', if set, will block any attempts to send events
+# until the user consents to the privacy policy. The value of the setting is
+# used as the text of the error.
+#
 # user_consent:
 #   template_dir: res/templates/privacy
 #   version: 1.0
 #   server_notice_content:
 #     msgtype: m.text
 #     body: |
 #       Pls do consent kthx
+#   block_events_error: |
+#     You can't send any messages until you consent to the privacy policy.
 """
 
 
@@ -51,6 +57,7 @@ def __init__(self):
         self.user_consent_version = None
         self.user_consent_template_dir = None
         self.user_consent_server_notice_content = None
+        self.block_events_without_consent_error = None
 
     def read_config(self, config):
         consent_config = config.get("user_consent")
@@ -61,6 +68,9 @@ def read_config(self, config):
         self.user_consent_server_notice_content = consent_config.get(
             "server_notice_content",
         )
+        self.block_events_without_consent_error = consent_config.get(
+            "block_events_error",
+        )
 
     def default_config(self, **kwargs):
         return DEFAULT_CONFIG

synapse/handlers/message.py

@@ -20,10 +20,15 @@
 from canonicaljson import encode_canonical_json
 import six
 from twisted.internet import defer, reactor
+from twisted.internet.defer import succeed
 from twisted.python.failure import Failure
 
 from synapse.api.constants import EventTypes, Membership, MAX_DEPTH
-from synapse.api.errors import AuthError, Codes, SynapseError
+from synapse.api.errors import (
+    AuthError, Codes, SynapseError,
+    ConsentNotGivenError,
+)
+from synapse.api.urls import ConsentURIBuilder
 from synapse.crypto.event_signing import add_hashes_and_signatures
 from synapse.events.utils import serialize_event
 from synapse.events.validator import EventValidator
@@ -431,6 +436,9 @@ def __init__(self, hs):
 
         self.spam_checker = hs.get_spam_checker()
 
+        if self.config.block_events_without_consent_error is not None:
+            self._consent_uri_builder = ConsentURIBuilder(self.config)
+
     @defer.inlineCallbacks
     def create_event(self, requester, event_dict, token_id=None, txn_id=None,
                      prev_events_and_hashes=None):
@@ -482,6 +490,10 @@ def create_event(self, requester, event_dict, token_id=None, txn_id=None,
                         target, e
                     )
 
+        is_exempt = yield self._is_exempt_from_privacy_policy(builder)
+        if not is_exempt:
+            yield self.assert_accepted_privacy_policy(requester)
+
         if token_id is not None:
             builder.internal_metadata.token_id = token_id
 
@@ -496,6 +508,78 @@ def create_event(self, requester, event_dict, token_id=None, txn_id=None,
 
         defer.returnValue((event, context))
 
+    def _is_exempt_from_privacy_policy(self, builder):
+        """"Determine if an event to be sent is exempt from having to consent
+        to the privacy policy
+
+        Args:
+            builder (synapse.events.builder.EventBuilder): event being created
+
+        Returns:
+            Deferred[bool]: true if the event can be sent without the user
+                consenting
+        """
+        # the only thing the user can do is join the server notices room.
+        if builder.type == EventTypes.Member:
+            membership = builder.content.get("membership", None)
+            if membership == Membership.JOIN:
+                return self._is_server_notices_room(builder.room_id)
+        return succeed(False)
+
+    @defer.inlineCallbacks
+    def _is_server_notices_room(self, room_id):
+        if self.config.server_notices_mxid is None:
+            defer.returnValue(False)
+        user_ids = yield self.store.get_users_in_room(room_id)
+        defer.returnValue(self.config.server_notices_mxid in user_ids)
+
+    @defer.inlineCallbacks
+    def assert_accepted_privacy_policy(self, requester):
+        """Check if a user has accepted the privacy policy
+
+        Called when the given user is about to do something that requires
+        privacy consent. We see if the user is exempt and otherwise check that
+        they have given consent. If they have not, a ConsentNotGiven error is
+        raised.
+
+        Args:
+            requester (synapse.types.Requester):
+                The user making the request
+
+        Returns:
+            Deferred[None]: returns normally if the user has consented or is
+                exempt
+
+        Raises:
+            ConsentNotGivenError: if the user has not given consent yet
+        """
+        if self.config.block_events_without_consent_error is None:
+            return
+
+        # exempt AS users from needing consent
+        if requester.app_service is not None:
+            return
+
+        user_id = requester.user.to_string()
+
+        # exempt the system notices user
+        if (
+            self.config.server_notices_mxid is not None and
+            user_id == self.config.server_notices_mxid
+        ):
+            return
+
+        u = yield self.store.get_user_by_id(user_id)
+        assert u is not None
+        if u["consent_version"] == self.config.user_consent_version:
+            return
+
+        consent_uri = self._consent_uri_builder.build_user_consent_uri(user_id)
+        raise ConsentNotGivenError(
+            msg=self.config.block_events_without_consent_error,
+            consent_uri=consent_uri,
+        )
+
     @defer.inlineCallbacks
     def send_nonmember_event(self, requester, event, context, ratelimit=True):
         """

synapse/handlers/room.py

@@ -126,6 +126,10 @@ def create_room(self, requester, config, ratelimit=True,
             except Exception:
                 raise SynapseError(400, "Invalid user_id: %s" % (i,))
 
+        yield self.event_creation_handler.assert_accepted_privacy_policy(
+            requester,
+        )
+
         invite_3pid_list = config.get("invite_3pid", [])
 
         visibility = config.get("visibility", None)

tests/utils.py

@@ -64,6 +64,7 @@ def setup_test_homeserver(name="test", datastore=None, config=None, **kargs):
         config.filter_timeline_limit = 5000
         config.user_directory_search_all_users = False
         config.user_consent_server_notice_content = None
+        config.block_events_without_consent_error = None
 
         # disable user directory updates, because they get done in the
         # background, which upsets the test runner.