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https://mau.dev/maunium/synapse.git
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88d7182ada
It's not really a problem to trust notary responses signed by the old key so long as we are also doing TLS validation. This commit adds a check to the config parsing code at startup to check that we do not have the insecure matrix.org key without tls validation, and refuses to start without it. This allows us to remove the rather alarming-looking warning which happens at runtime.
369 lines
14 KiB
Python
369 lines
14 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2015, 2016 OpenMarket Ltd
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# Copyright 2019 The Matrix.org Foundation C.I.C.
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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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import hashlib
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import logging
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import os
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import attr
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import jsonschema
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from signedjson.key import (
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NACL_ED25519,
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decode_signing_key_base64,
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decode_verify_key_bytes,
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generate_signing_key,
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is_signing_algorithm_supported,
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read_signing_keys,
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write_signing_keys,
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)
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from unpaddedbase64 import decode_base64
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from synapse.util.stringutils import random_string, random_string_with_symbols
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from ._base import Config, ConfigError
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INSECURE_NOTARY_ERROR = """\
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Your server is configured to accept key server responses without signature
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validation or TLS certificate validation. This is likely to be very insecure. If
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you are *sure* you want to do this, set 'accept_keys_insecurely' on the
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keyserver configuration."""
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RELYING_ON_MATRIX_KEY_ERROR = """\
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Your server is configured to accept key server responses without TLS certificate
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validation, and which are only signed by the old (possibly compromised)
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matrix.org signing key 'ed25519:auto'. This likely isn't what you want to do,
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and you should enable 'federation_verify_certificates' in your configuration.
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If you are *sure* you want to do this, set 'accept_keys_insecurely' on the
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trusted_key_server configuration."""
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logger = logging.getLogger(__name__)
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@attr.s
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class TrustedKeyServer(object):
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# string: name of the server.
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server_name = attr.ib()
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# dict[str,VerifyKey]|None: map from key id to key object, or None to disable
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# signature verification.
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verify_keys = attr.ib(default=None)
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class KeyConfig(Config):
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def read_config(self, config):
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# the signing key can be specified inline or in a separate file
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if "signing_key" in config:
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self.signing_key = read_signing_keys([config["signing_key"]])
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else:
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self.signing_key_path = config["signing_key_path"]
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self.signing_key = self.read_signing_key(self.signing_key_path)
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self.old_signing_keys = self.read_old_signing_keys(
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config.get("old_signing_keys", {})
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)
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self.key_refresh_interval = self.parse_duration(
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config.get("key_refresh_interval", "1d")
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)
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# if neither trusted_key_servers nor perspectives are given, use the default.
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if "perspectives" not in config and "trusted_key_servers" not in config:
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key_servers = [{"server_name": "matrix.org"}]
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else:
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key_servers = config.get("trusted_key_servers", [])
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if not isinstance(key_servers, list):
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raise ConfigError(
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"trusted_key_servers, if given, must be a list, not a %s"
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% (type(key_servers).__name__,)
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)
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# merge the 'perspectives' config into the 'trusted_key_servers' config.
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key_servers.extend(_perspectives_to_key_servers(config))
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# list of TrustedKeyServer objects
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self.key_servers = list(
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_parse_key_servers(key_servers, self.federation_verify_certificates)
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)
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self.macaroon_secret_key = config.get(
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"macaroon_secret_key", self.registration_shared_secret
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)
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if not self.macaroon_secret_key:
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# Unfortunately, there are people out there that don't have this
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# set. Lets just be "nice" and derive one from their secret key.
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logger.warn("Config is missing macaroon_secret_key")
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seed = bytes(self.signing_key[0])
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self.macaroon_secret_key = hashlib.sha256(seed).digest()
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self.expire_access_token = config.get("expire_access_token", False)
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# a secret which is used to calculate HMACs for form values, to stop
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# falsification of values
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self.form_secret = config.get("form_secret", None)
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def default_config(
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self, config_dir_path, server_name, generate_secrets=False, **kwargs
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):
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base_key_name = os.path.join(config_dir_path, server_name)
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if generate_secrets:
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macaroon_secret_key = 'macaroon_secret_key: "%s"' % (
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random_string_with_symbols(50),
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)
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form_secret = 'form_secret: "%s"' % random_string_with_symbols(50)
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else:
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macaroon_secret_key = "# macaroon_secret_key: <PRIVATE STRING>"
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form_secret = "# form_secret: <PRIVATE STRING>"
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return (
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"""\
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# a secret which is used to sign access tokens. If none is specified,
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# the registration_shared_secret is used, if one is given; otherwise,
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# a secret key is derived from the signing key.
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#
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%(macaroon_secret_key)s
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# Used to enable access token expiration.
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#
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#expire_access_token: False
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# a secret which is used to calculate HMACs for form values, to stop
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# falsification of values. Must be specified for the User Consent
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# forms to work.
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#
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%(form_secret)s
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## Signing Keys ##
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# Path to the signing key to sign messages with
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#
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signing_key_path: "%(base_key_name)s.signing.key"
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# The keys that the server used to sign messages with but won't use
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# to sign new messages. E.g. it has lost its private key
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#
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#old_signing_keys:
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# "ed25519:auto":
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# # Base64 encoded public key
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# key: "The public part of your old signing key."
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# # Millisecond POSIX timestamp when the key expired.
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# expired_ts: 123456789123
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# How long key response published by this server is valid for.
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# Used to set the valid_until_ts in /key/v2 APIs.
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# Determines how quickly servers will query to check which keys
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# are still valid.
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#
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#key_refresh_interval: 1d
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# The trusted servers to download signing keys from.
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#
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# When we need to fetch a signing key, each server is tried in parallel.
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#
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# Normally, the connection to the key server is validated via TLS certificates.
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# Additional security can be provided by configuring a `verify key`, which
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# will make synapse check that the response is signed by that key.
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#
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# This setting supercedes an older setting named `perspectives`. The old format
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# is still supported for backwards-compatibility, but it is deprecated.
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#
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# Options for each entry in the list include:
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#
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# server_name: the name of the server. required.
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#
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# verify_keys: an optional map from key id to base64-encoded public key.
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# If specified, we will check that the response is signed by at least
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# one of the given keys.
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#
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# accept_keys_insecurely: a boolean. Normally, if `verify_keys` is unset,
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# and federation_verify_certificates is not `true`, synapse will refuse
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# to start, because this would allow anyone who can spoof DNS responses
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# to masquerade as the trusted key server. If you know what you are doing
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# and are sure that your network environment provides a secure connection
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# to the key server, you can set this to `true` to override this
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# behaviour.
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#
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# An example configuration might look like:
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#
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#trusted_key_servers:
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# - server_name: "my_trusted_server.example.com"
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# verify_keys:
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# "ed25519:auto": "abcdefghijklmnopqrstuvwxyzabcdefghijklmopqr"
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# - server_name: "my_other_trusted_server.example.com"
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#
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# The default configuration is:
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#
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#trusted_key_servers:
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# - server_name: "matrix.org"
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"""
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% locals()
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)
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def read_signing_key(self, signing_key_path):
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signing_keys = self.read_file(signing_key_path, "signing_key")
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try:
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return read_signing_keys(signing_keys.splitlines(True))
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except Exception as e:
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raise ConfigError("Error reading signing_key: %s" % (str(e)))
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def read_old_signing_keys(self, old_signing_keys):
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keys = {}
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for key_id, key_data in old_signing_keys.items():
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if is_signing_algorithm_supported(key_id):
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key_base64 = key_data["key"]
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key_bytes = decode_base64(key_base64)
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verify_key = decode_verify_key_bytes(key_id, key_bytes)
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verify_key.expired_ts = key_data["expired_ts"]
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keys[key_id] = verify_key
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else:
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raise ConfigError(
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"Unsupported signing algorithm for old key: %r" % (key_id,)
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)
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return keys
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def generate_files(self, config):
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signing_key_path = config["signing_key_path"]
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if not self.path_exists(signing_key_path):
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with open(signing_key_path, "w") as signing_key_file:
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key_id = "a_" + random_string(4)
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write_signing_keys(signing_key_file, (generate_signing_key(key_id),))
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else:
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signing_keys = self.read_file(signing_key_path, "signing_key")
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if len(signing_keys.split("\n")[0].split()) == 1:
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# handle keys in the old format.
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key_id = "a_" + random_string(4)
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key = decode_signing_key_base64(
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NACL_ED25519, key_id, signing_keys.split("\n")[0]
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)
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with open(signing_key_path, "w") as signing_key_file:
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write_signing_keys(signing_key_file, (key,))
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def _perspectives_to_key_servers(config):
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"""Convert old-style 'perspectives' configs into new-style 'trusted_key_servers'
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Returns an iterable of entries to add to trusted_key_servers.
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"""
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# 'perspectives' looks like:
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#
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# {
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# "servers": {
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# "matrix.org": {
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# "verify_keys": {
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# "ed25519:auto": {
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# "key": "Noi6WqcDj0QmPxCNQqgezwTlBKrfqehY1u2FyWP9uYw"
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# }
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# }
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# }
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# }
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# }
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#
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# 'trusted_keys' looks like:
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#
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# [
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# {
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# "server_name": "matrix.org",
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# "verify_keys": {
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# "ed25519:auto": "Noi6WqcDj0QmPxCNQqgezwTlBKrfqehY1u2FyWP9uYw",
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# }
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# }
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# ]
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perspectives_servers = config.get("perspectives", {}).get("servers", {})
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for server_name, server_opts in perspectives_servers.items():
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trusted_key_server_entry = {"server_name": server_name}
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verify_keys = server_opts.get("verify_keys")
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if verify_keys is not None:
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trusted_key_server_entry["verify_keys"] = {
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key_id: key_data["key"] for key_id, key_data in verify_keys.items()
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}
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yield trusted_key_server_entry
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TRUSTED_KEY_SERVERS_SCHEMA = {
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"$schema": "http://json-schema.org/draft-04/schema#",
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"description": "schema for the trusted_key_servers setting",
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"type": "array",
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"items": {
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"type": "object",
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"properties": {
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"server_name": {"type": "string"},
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"verify_keys": {
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"type": "object",
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# each key must be a base64 string
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"additionalProperties": {"type": "string"},
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},
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},
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"required": ["server_name"],
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},
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}
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def _parse_key_servers(key_servers, federation_verify_certificates):
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try:
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jsonschema.validate(key_servers, TRUSTED_KEY_SERVERS_SCHEMA)
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except jsonschema.ValidationError as e:
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raise ConfigError("Unable to parse 'trusted_key_servers': " + e.message)
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for server in key_servers:
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server_name = server["server_name"]
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result = TrustedKeyServer(server_name=server_name)
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verify_keys = server.get("verify_keys")
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if verify_keys is not None:
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result.verify_keys = {}
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for key_id, key_base64 in verify_keys.items():
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if not is_signing_algorithm_supported(key_id):
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raise ConfigError(
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"Unsupported signing algorithm on key %s for server %s in "
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"trusted_key_servers" % (key_id, server_name)
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)
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try:
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key_bytes = decode_base64(key_base64)
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verify_key = decode_verify_key_bytes(key_id, key_bytes)
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except Exception as e:
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raise ConfigError(
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"Unable to parse key %s for server %s in "
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"trusted_key_servers: %s" % (key_id, server_name, e)
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)
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result.verify_keys[key_id] = verify_key
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if (
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not federation_verify_certificates and
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not server.get("accept_keys_insecurely")
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):
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_assert_keyserver_has_verify_keys(result)
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yield result
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def _assert_keyserver_has_verify_keys(trusted_key_server):
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if not trusted_key_server.verify_keys:
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raise ConfigError(INSECURE_NOTARY_ERROR)
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# also check that they are not blindly checking the old matrix.org key
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if trusted_key_server.server_name == "matrix.org" and any(
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key_id == "ed25519:auto" for key_id in trusted_key_server.verify_keys
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):
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raise ConfigError(RELYING_ON_MATRIX_KEY_ERROR)
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