anonymousland-synapse/synapse/handlers/saml_handler.py
Richard van der Hoff 0cb169900e
Implement login blocking based on SAML attributes (#8052)
Hopefully this mostly speaks for itself. I also did a bit of cleaning up of the
error handling.

Fixes #8047
2020-08-11 16:08:10 +01:00

470 lines
18 KiB
Python

# -*- coding: utf-8 -*-
# Copyright 2019 The Matrix.org Foundation C.I.C.
#
# 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.
import logging
import re
from typing import TYPE_CHECKING, Callable, Dict, Optional, Set, Tuple
import attr
import saml2
import saml2.response
from saml2.client import Saml2Client
from synapse.api.errors import AuthError, SynapseError
from synapse.config import ConfigError
from synapse.config.saml2_config import SamlAttributeRequirement
from synapse.http.servlet import parse_string
from synapse.http.site import SynapseRequest
from synapse.module_api import ModuleApi
from synapse.types import (
UserID,
map_username_to_mxid_localpart,
mxid_localpart_allowed_characters,
)
from synapse.util.async_helpers import Linearizer
from synapse.util.iterutils import chunk_seq
if TYPE_CHECKING:
import synapse.server
logger = logging.getLogger(__name__)
@attr.s
class Saml2SessionData:
"""Data we track about SAML2 sessions"""
# time the session was created, in milliseconds
creation_time = attr.ib()
# The user interactive authentication session ID associated with this SAML
# session (or None if this SAML session is for an initial login).
ui_auth_session_id = attr.ib(type=Optional[str], default=None)
class SamlHandler:
def __init__(self, hs: "synapse.server.HomeServer"):
self._saml_client = Saml2Client(hs.config.saml2_sp_config)
self._auth = hs.get_auth()
self._auth_handler = hs.get_auth_handler()
self._registration_handler = hs.get_registration_handler()
self._clock = hs.get_clock()
self._datastore = hs.get_datastore()
self._hostname = hs.hostname
self._saml2_session_lifetime = hs.config.saml2_session_lifetime
self._grandfathered_mxid_source_attribute = (
hs.config.saml2_grandfathered_mxid_source_attribute
)
self._saml2_attribute_requirements = hs.config.saml2.attribute_requirements
# plugin to do custom mapping from saml response to mxid
self._user_mapping_provider = hs.config.saml2_user_mapping_provider_class(
hs.config.saml2_user_mapping_provider_config,
ModuleApi(hs, hs.get_auth_handler()),
)
# identifier for the external_ids table
self._auth_provider_id = "saml"
# a map from saml session id to Saml2SessionData object
self._outstanding_requests_dict = {} # type: Dict[str, Saml2SessionData]
# a lock on the mappings
self._mapping_lock = Linearizer(name="saml_mapping", clock=self._clock)
def handle_redirect_request(
self, client_redirect_url: bytes, ui_auth_session_id: Optional[str] = None
) -> bytes:
"""Handle an incoming request to /login/sso/redirect
Args:
client_redirect_url: the URL that we should redirect the
client to when everything is done
ui_auth_session_id: The session ID of the ongoing UI Auth (or
None if this is a login).
Returns:
URL to redirect to
"""
reqid, info = self._saml_client.prepare_for_authenticate(
relay_state=client_redirect_url
)
# Since SAML sessions timeout it is useful to log when they were created.
logger.info("Initiating a new SAML session: %s" % (reqid,))
now = self._clock.time_msec()
self._outstanding_requests_dict[reqid] = Saml2SessionData(
creation_time=now, ui_auth_session_id=ui_auth_session_id,
)
for key, value in info["headers"]:
if key == "Location":
return value
# this shouldn't happen!
raise Exception("prepare_for_authenticate didn't return a Location header")
async def handle_saml_response(self, request: SynapseRequest) -> None:
"""Handle an incoming request to /_matrix/saml2/authn_response
Args:
request: the incoming request from the browser. We'll
respond to it with a redirect.
Returns:
Completes once we have handled the request.
"""
resp_bytes = parse_string(request, "SAMLResponse", required=True)
relay_state = parse_string(request, "RelayState", required=True)
# expire outstanding sessions before parse_authn_request_response checks
# the dict.
self.expire_sessions()
user_id, current_session = await self._map_saml_response_to_user(
resp_bytes, relay_state
)
# Complete the interactive auth session or the login.
if current_session and current_session.ui_auth_session_id:
await self._auth_handler.complete_sso_ui_auth(
user_id, current_session.ui_auth_session_id, request
)
else:
await self._auth_handler.complete_sso_login(user_id, request, relay_state)
async def _map_saml_response_to_user(
self, resp_bytes: str, client_redirect_url: str
) -> Tuple[str, Optional[Saml2SessionData]]:
"""
Given a sample response, retrieve the cached session and user for it.
Args:
resp_bytes: The SAML response.
client_redirect_url: The redirect URL passed in by the client.
Returns:
Tuple of the user ID and SAML session associated with this response.
Raises:
SynapseError if there was a problem with the response.
RedirectException: some mapping providers may raise this if they need
to redirect to an interstitial page.
"""
try:
saml2_auth = self._saml_client.parse_authn_request_response(
resp_bytes,
saml2.BINDING_HTTP_POST,
outstanding=self._outstanding_requests_dict,
)
except saml2.response.UnsolicitedResponse as e:
# the pysaml2 library helpfully logs an ERROR here, but neglects to log
# the session ID. I don't really want to put the full text of the exception
# in the (user-visible) exception message, so let's log the exception here
# so we can track down the session IDs later.
logger.warning(str(e))
raise SynapseError(400, "Unexpected SAML2 login.")
except Exception as e:
raise SynapseError(400, "Unable to parse SAML2 response: %s." % (e,))
if saml2_auth.not_signed:
raise SynapseError(400, "SAML2 response was not signed.")
logger.debug("SAML2 response: %s", saml2_auth.origxml)
for assertion in saml2_auth.assertions:
# kibana limits the length of a log field, whereas this is all rather
# useful, so split it up.
count = 0
for part in chunk_seq(str(assertion), 10000):
logger.info(
"SAML2 assertion: %s%s", "(%i)..." % (count,) if count else "", part
)
count += 1
logger.info("SAML2 mapped attributes: %s", saml2_auth.ava)
current_session = self._outstanding_requests_dict.pop(
saml2_auth.in_response_to, None
)
for requirement in self._saml2_attribute_requirements:
_check_attribute_requirement(saml2_auth.ava, requirement)
remote_user_id = self._user_mapping_provider.get_remote_user_id(
saml2_auth, client_redirect_url
)
if not remote_user_id:
raise Exception("Failed to extract remote user id from SAML response")
with (await self._mapping_lock.queue(self._auth_provider_id)):
# first of all, check if we already have a mapping for this user
logger.info(
"Looking for existing mapping for user %s:%s",
self._auth_provider_id,
remote_user_id,
)
registered_user_id = await self._datastore.get_user_by_external_id(
self._auth_provider_id, remote_user_id
)
if registered_user_id is not None:
logger.info("Found existing mapping %s", registered_user_id)
return registered_user_id, current_session
# backwards-compatibility hack: see if there is an existing user with a
# suitable mapping from the uid
if (
self._grandfathered_mxid_source_attribute
and self._grandfathered_mxid_source_attribute in saml2_auth.ava
):
attrval = saml2_auth.ava[self._grandfathered_mxid_source_attribute][0]
user_id = UserID(
map_username_to_mxid_localpart(attrval), self._hostname
).to_string()
logger.info(
"Looking for existing account based on mapped %s %s",
self._grandfathered_mxid_source_attribute,
user_id,
)
users = await self._datastore.get_users_by_id_case_insensitive(user_id)
if users:
registered_user_id = list(users.keys())[0]
logger.info("Grandfathering mapping to %s", registered_user_id)
await self._datastore.record_user_external_id(
self._auth_provider_id, remote_user_id, registered_user_id
)
return registered_user_id, current_session
# Map saml response to user attributes using the configured mapping provider
for i in range(1000):
attribute_dict = self._user_mapping_provider.saml_response_to_user_attributes(
saml2_auth, i, client_redirect_url=client_redirect_url,
)
logger.debug(
"Retrieved SAML attributes from user mapping provider: %s "
"(attempt %d)",
attribute_dict,
i,
)
localpart = attribute_dict.get("mxid_localpart")
if not localpart:
raise Exception(
"Error parsing SAML2 response: SAML mapping provider plugin "
"did not return a mxid_localpart value"
)
displayname = attribute_dict.get("displayname")
emails = attribute_dict.get("emails", [])
# Check if this mxid already exists
if not await self._datastore.get_users_by_id_case_insensitive(
UserID(localpart, self._hostname).to_string()
):
# This mxid is free
break
else:
# Unable to generate a username in 1000 iterations
# Break and return error to the user
raise SynapseError(
500, "Unable to generate a Matrix ID from the SAML response"
)
logger.info("Mapped SAML user to local part %s", localpart)
registered_user_id = await self._registration_handler.register_user(
localpart=localpart,
default_display_name=displayname,
bind_emails=emails,
)
await self._datastore.record_user_external_id(
self._auth_provider_id, remote_user_id, registered_user_id
)
return registered_user_id, current_session
def expire_sessions(self):
expire_before = self._clock.time_msec() - self._saml2_session_lifetime
to_expire = set()
for reqid, data in self._outstanding_requests_dict.items():
if data.creation_time < expire_before:
to_expire.add(reqid)
for reqid in to_expire:
logger.debug("Expiring session id %s", reqid)
del self._outstanding_requests_dict[reqid]
def _check_attribute_requirement(ava: dict, req: SamlAttributeRequirement):
values = ava.get(req.attribute, [])
for v in values:
if v == req.value:
return
logger.info(
"SAML2 attribute %s did not match required value '%s' (was '%s')",
req.attribute,
req.value,
values,
)
raise AuthError(403, "You are not authorized to log in here.")
DOT_REPLACE_PATTERN = re.compile(
("[^%s]" % (re.escape("".join(mxid_localpart_allowed_characters)),))
)
def dot_replace_for_mxid(username: str) -> str:
"""Replace any characters which are not allowed in Matrix IDs with a dot."""
username = username.lower()
username = DOT_REPLACE_PATTERN.sub(".", username)
# regular mxids aren't allowed to start with an underscore either
username = re.sub("^_", "", username)
return username
MXID_MAPPER_MAP = {
"hexencode": map_username_to_mxid_localpart,
"dotreplace": dot_replace_for_mxid,
} # type: Dict[str, Callable[[str], str]]
@attr.s
class SamlConfig(object):
mxid_source_attribute = attr.ib()
mxid_mapper = attr.ib()
class DefaultSamlMappingProvider(object):
__version__ = "0.0.1"
def __init__(self, parsed_config: SamlConfig, module_api: ModuleApi):
"""The default SAML user mapping provider
Args:
parsed_config: Module configuration
module_api: module api proxy
"""
self._mxid_source_attribute = parsed_config.mxid_source_attribute
self._mxid_mapper = parsed_config.mxid_mapper
self._grandfathered_mxid_source_attribute = (
module_api._hs.config.saml2_grandfathered_mxid_source_attribute
)
def get_remote_user_id(
self, saml_response: saml2.response.AuthnResponse, client_redirect_url: str
) -> str:
"""Extracts the remote user id from the SAML response"""
try:
return saml_response.ava["uid"][0]
except KeyError:
logger.warning("SAML2 response lacks a 'uid' attestation")
raise SynapseError(400, "'uid' not in SAML2 response")
def saml_response_to_user_attributes(
self,
saml_response: saml2.response.AuthnResponse,
failures: int,
client_redirect_url: str,
) -> dict:
"""Maps some text from a SAML response to attributes of a new user
Args:
saml_response: A SAML auth response object
failures: How many times a call to this function with this
saml_response has resulted in a failure
client_redirect_url: where the client wants to redirect to
Returns:
dict: A dict containing new user attributes. Possible keys:
* mxid_localpart (str): Required. The localpart of the user's mxid
* displayname (str): The displayname of the user
* emails (list[str]): Any emails for the user
"""
try:
mxid_source = saml_response.ava[self._mxid_source_attribute][0]
except KeyError:
logger.warning(
"SAML2 response lacks a '%s' attestation", self._mxid_source_attribute,
)
raise SynapseError(
400, "%s not in SAML2 response" % (self._mxid_source_attribute,)
)
# Use the configured mapper for this mxid_source
base_mxid_localpart = self._mxid_mapper(mxid_source)
# Append suffix integer if last call to this function failed to produce
# a usable mxid
localpart = base_mxid_localpart + (str(failures) if failures else "")
# Retrieve the display name from the saml response
# If displayname is None, the mxid_localpart will be used instead
displayname = saml_response.ava.get("displayName", [None])[0]
# Retrieve any emails present in the saml response
emails = saml_response.ava.get("email", [])
return {
"mxid_localpart": localpart,
"displayname": displayname,
"emails": emails,
}
@staticmethod
def parse_config(config: dict) -> SamlConfig:
"""Parse the dict provided by the homeserver's config
Args:
config: A dictionary containing configuration options for this provider
Returns:
SamlConfig: A custom config object for this module
"""
# Parse config options and use defaults where necessary
mxid_source_attribute = config.get("mxid_source_attribute", "uid")
mapping_type = config.get("mxid_mapping", "hexencode")
# Retrieve the associating mapping function
try:
mxid_mapper = MXID_MAPPER_MAP[mapping_type]
except KeyError:
raise ConfigError(
"saml2_config.user_mapping_provider.config: '%s' is not a valid "
"mxid_mapping value" % (mapping_type,)
)
return SamlConfig(mxid_source_attribute, mxid_mapper)
@staticmethod
def get_saml_attributes(config: SamlConfig) -> Tuple[Set[str], Set[str]]:
"""Returns the required attributes of a SAML
Args:
config: A SamlConfig object containing configuration params for this provider
Returns:
The first set equates to the saml auth response
attributes that are required for the module to function, whereas the
second set consists of those attributes which can be used if
available, but are not necessary
"""
return {"uid", config.mxid_source_attribute}, {"displayName", "email"}