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Diffstat (limited to 'synapse/groups/attestations.py')
| -rw-r--r-- | synapse/groups/attestations.py | 198 |
1 files changed, 198 insertions, 0 deletions
diff --git a/synapse/groups/attestations.py b/synapse/groups/attestations.py new file mode 100644 index 0000000000..47452700a8 --- /dev/null +++ b/synapse/groups/attestations.py @@ -0,0 +1,198 @@ +# -*- coding: utf-8 -*- +# Copyright 2017 Vector Creations Ltd +# +# Licensed under the Apache License, Version 2.0 (the "License"); +# you may not use this file except in compliance with the License. +# You may obtain a copy of the License at +# +# http://www.apache.org/licenses/LICENSE-2.0 +# +# Unless required by applicable law or agreed to in writing, software +# distributed under the License is distributed on an "AS IS" BASIS, +# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +# See the License for the specific language governing permissions and +# limitations under the License. + +"""Attestations ensure that users and groups can't lie about their memberships. + +When a user joins a group the HS and GS swap attestations, which allow them +both to independently prove to third parties their membership.These +attestations have a validity period so need to be periodically renewed. + +If a user leaves (or gets kicked out of) a group, either side can still use +their attestation to "prove" their membership, until the attestation expires. +Therefore attestations shouldn't be relied on to prove membership in important +cases, but can for less important situtations, e.g. showing a users membership +of groups on their profile, showing flairs, etc. + +An attestation is a signed blob of json that looks like: + + { + "user_id": "@foo:a.example.com", + "group_id": "+bar:b.example.com", + "valid_until_ms": 1507994728530, + "signatures":{"matrix.org":{"ed25519:auto":"..."}} + } +""" + +import logging +import random + +from signedjson.sign import sign_json + +from twisted.internet import defer + +from synapse.api.errors import SynapseError +from synapse.types import get_domain_from_id +from synapse.util.logcontext import run_in_background + +logger = logging.getLogger(__name__) + + +# Default validity duration for new attestations we create +DEFAULT_ATTESTATION_LENGTH_MS = 3 * 24 * 60 * 60 * 1000 + +# We add some jitter to the validity duration of attestations so that if we +# add lots of users at once we don't need to renew them all at once. +# The jitter is a multiplier picked randomly between the first and second number +DEFAULT_ATTESTATION_JITTER = (0.9, 1.3) + +# Start trying to update our attestations when they come this close to expiring +UPDATE_ATTESTATION_TIME_MS = 1 * 24 * 60 * 60 * 1000 + + +class GroupAttestationSigning(object): + """Creates and verifies group attestations. + """ + def __init__(self, hs): + self.keyring = hs.get_keyring() + self.clock = hs.get_clock() + self.server_name = hs.hostname + self.signing_key = hs.config.signing_key[0] + + @defer.inlineCallbacks + def verify_attestation(self, attestation, group_id, user_id, server_name=None): + """Verifies that the given attestation matches the given parameters. + + An optional server_name can be supplied to explicitly set which server's + signature is expected. Otherwise assumes that either the group_id or user_id + is local and uses the other's server as the one to check. + """ + + if not server_name: + if get_domain_from_id(group_id) == self.server_name: + server_name = get_domain_from_id(user_id) + elif get_domain_from_id(user_id) == self.server_name: + server_name = get_domain_from_id(group_id) + else: + raise Exception("Expected either group_id or user_id to be local") + + if user_id != attestation["user_id"]: + raise SynapseError(400, "Attestation has incorrect user_id") + + if group_id != attestation["group_id"]: + raise SynapseError(400, "Attestation has incorrect group_id") + valid_until_ms = attestation["valid_until_ms"] + + # TODO: We also want to check that *new* attestations that people give + # us to store are valid for at least a little while. + if valid_until_ms < self.clock.time_msec(): + raise SynapseError(400, "Attestation expired") + + yield self.keyring.verify_json_for_server(server_name, attestation) + + def create_attestation(self, group_id, user_id): + """Create an attestation for the group_id and user_id with default + validity length. + """ + validity_period = DEFAULT_ATTESTATION_LENGTH_MS + validity_period *= random.uniform(*DEFAULT_ATTESTATION_JITTER) + valid_until_ms = int(self.clock.time_msec() + validity_period) + + return sign_json({ + "group_id": group_id, + "user_id": user_id, + "valid_until_ms": valid_until_ms, + }, self.server_name, self.signing_key) + + +class GroupAttestionRenewer(object): + """Responsible for sending and receiving attestation updates. + """ + + def __init__(self, hs): + self.clock = hs.get_clock() + self.store = hs.get_datastore() + self.assestations = hs.get_groups_attestation_signing() + self.transport_client = hs.get_federation_transport_client() + self.is_mine_id = hs.is_mine_id + self.attestations = hs.get_groups_attestation_signing() + + self._renew_attestations_loop = self.clock.looping_call( + self._renew_attestations, 30 * 60 * 1000, + ) + + @defer.inlineCallbacks + def on_renew_attestation(self, group_id, user_id, content): + """When a remote updates an attestation + """ + attestation = content["attestation"] + + if not self.is_mine_id(group_id) and not self.is_mine_id(user_id): + raise SynapseError(400, "Neither user not group are on this server") + + yield self.attestations.verify_attestation( + attestation, + user_id=user_id, + group_id=group_id, + ) + + yield self.store.update_remote_attestion(group_id, user_id, attestation) + + defer.returnValue({}) + + @defer.inlineCallbacks + def _renew_attestations(self): + """Called periodically to check if we need to update any of our attestations + """ + + now = self.clock.time_msec() + + rows = yield self.store.get_attestations_need_renewals( + now + UPDATE_ATTESTATION_TIME_MS + ) + + @defer.inlineCallbacks + def _renew_attestation(group_id, user_id): + try: + if not self.is_mine_id(group_id): + destination = get_domain_from_id(group_id) + elif not self.is_mine_id(user_id): + destination = get_domain_from_id(user_id) + else: + logger.warn( + "Incorrectly trying to do attestations for user: %r in %r", + user_id, group_id, + ) + yield self.store.remove_attestation_renewal(group_id, user_id) + return + + attestation = self.attestations.create_attestation(group_id, user_id) + + yield self.transport_client.renew_group_attestation( + destination, group_id, user_id, + content={"attestation": attestation}, + ) + + yield self.store.update_attestation_renewal( + group_id, user_id, attestation + ) + except Exception: + logger.exception("Error renewing attestation of %r in %r", + user_id, group_id) + + for row in rows: + group_id = row["group_id"] + user_id = row["user_id"] + + run_in_background(_renew_attestation, group_id, user_id) |