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