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Clean up exception handling in SAML2ResponseResource (#7614)

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* Expose `return_html_error`, and allow it to take a Jinja2 template instead of a raw string

* Clean up exception handling in SAML2ResponseResource

  * use the existing code in `return_html_error` instead of re-implementing it
    (giving it a jinja2 template rather than inventing a new form of template)

  * do the exception-catching in the REST layer rather than in the handler
    layer, to make sure we catch all exceptions.
This commit is contained in:
Richard van der Hoff 2020-06-03 10:41:12 +01:00 committed by GitHub
parent 816589b09a
commit 1bbc9e2df6
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7 changed files with 77 additions and 61 deletions
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1
changelog.d/7614.misc Normal file
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@ -0,0 +1 @@
Clean up exception handling in `SAML2ResponseResource`.

8
docs/sample_config.yaml
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@ -1512,7 +1512,13 @@ saml2_config:
# * HTML page to display to users if something goes wrong during the
# authentication process: 'saml_error.html'.
#
# This template doesn't currently need any variable to render.
# When rendering, this template is given the following variables:
# * code: an HTML error code corresponding to the error that is being
# returned (typically 400 or 500)
#
# * msg: a textual message describing the error.
#
# The variables will automatically be HTML-escaped.
#
# You can see the default templates at:
# https://github.com/matrix-org/synapse/tree/master/synapse/res/templates

18
synapse/config/saml2_config.py
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@ -15,8 +15,8 @@
# limitations under the License.
import logging
import os
import jinja2
import pkg_resources
from synapse.python_dependencies import DependencyException, check_requirements
@ -167,9 +167,11 @@ class SAML2Config(Config):
if not template_dir:
template_dir = pkg_resources.resource_filename("synapse", "res/templates",)
self.saml2_error_html_content = self.read_file(
os.path.join(template_dir, "saml_error.html"), "saml2_config.saml_error",
)
loader = jinja2.FileSystemLoader(template_dir)
# enable auto-escape here, to having to remember to escape manually in the
# template
env = jinja2.Environment(loader=loader, autoescape=True)
self.saml2_error_html_template = env.get_template("saml_error.html")
def _default_saml_config_dict(
self, required_attributes: set, optional_attributes: set
@ -349,7 +351,13 @@ class SAML2Config(Config):
# * HTML page to display to users if something goes wrong during the
# authentication process: 'saml_error.html'.
#
# This template doesn't currently need any variable to render.
# When rendering, this template is given the following variables:
# * code: an HTML error code corresponding to the error that is being
# returned (typically 400 or 500)
#
# * msg: a textual message describing the error.
#
# The variables will automatically be HTML-escaped.
#
# You can see the default templates at:
# https://github.com/matrix-org/synapse/tree/master/synapse/res/templates

35
synapse/handlers/saml_handler.py
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@ -23,11 +23,9 @@ from saml2.client import Saml2Client
from synapse.api.errors import SynapseError
from synapse.config import ConfigError
from synapse.http.server import finish_request
from synapse.http.servlet import parse_string
from synapse.http.site import SynapseRequest
from synapse.module_api import ModuleApi
from synapse.module_api.errors import RedirectException
from synapse.types import (
UserID,
map_username_to_mxid_localpart,
@ -80,8 +78,6 @@ class SamlHandler:
# a lock on the mappings
self._mapping_lock = Linearizer(name="saml_mapping", clock=self._clock)
self._error_html_content = hs.config.saml2_error_html_content
def handle_redirect_request(
self, client_redirect_url: bytes, ui_auth_session_id: Optional[str] = None
) -> bytes:
@ -129,26 +125,9 @@ class SamlHandler:
# the dict.
self.expire_sessions()
try:
user_id, current_session = await self._map_saml_response_to_user(
resp_bytes, relay_state
)
except RedirectException:
# Raise the exception as per the wishes of the SAML module response
raise
except Exception as e:
# If decoding the response or mapping it to a user failed, then log the
# error and tell the user that something went wrong.
logger.error(e)
request.setResponseCode(400)
request.setHeader(b"Content-Type", b"text/html; charset=utf-8")
request.setHeader(
b"Content-Length", b"%d" % (len(self._error_html_content),)
)
request.write(self._error_html_content.encode("utf8"))
finish_request(request)
return
# Complete the interactive auth session or the login.
if current_session and current_session.ui_auth_session_id:
@ -171,6 +150,11 @@ class SamlHandler:
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(
@ -179,11 +163,9 @@ class SamlHandler:
outstanding=self._outstanding_requests_dict,
)
except Exception as e:
logger.warning("Exception parsing SAML2 response: %s", e)
raise SynapseError(400, "Unable to parse SAML2 response: %s" % (e,))
if saml2_auth.not_signed:
logger.warning("SAML2 response was not signed")
raise SynapseError(400, "SAML2 response was not signed")
logger.debug("SAML2 response: %s", saml2_auth.origxml)
@ -264,11 +246,10 @@ class SamlHandler:
localpart = attribute_dict.get("mxid_localpart")
if not localpart:
logger.error(
"SAML mapping provider plugin did not return a "
"mxid_localpart object"
raise Exception(
"Error parsing SAML2 response: SAML mapping provider plugin "
"did not return a mxid_localpart value"
)
raise SynapseError(500, "Error parsing SAML2 response")
displayname = attribute_dict.get("displayname")
emails = attribute_dict.get("emails", [])

43
synapse/http/server.py
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@ -21,13 +21,15 @@ import logging
import types
import urllib
from io import BytesIO
from typing import Awaitable, Callable, TypeVar, Union
import jinja2
from canonicaljson import encode_canonical_json, encode_pretty_printed_json, json
from twisted.internet import defer
from twisted.python import failure
from twisted.web import resource
from twisted.web.server import NOT_DONE_YET
from twisted.web.server import NOT_DONE_YET, Request
from twisted.web.static import NoRangeStaticProducer
from twisted.web.util import redirectTo
@ -40,6 +42,7 @@ from synapse.api.errors import (
SynapseError,
UnrecognizedRequestError,
)
from synapse.http.site import SynapseRequest
from synapse.logging.context import preserve_fn
from synapse.logging.opentracing import trace_servlet
from synapse.util.caches import intern_dict
@ -130,7 +133,12 @@ def wrap_json_request_handler(h):
return wrap_async_request_handler(wrapped_request_handler)
def wrap_html_request_handler(h):
TV = TypeVar("TV")
def wrap_html_request_handler(
h: Callable[[TV, SynapseRequest], Awaitable]
) -> Callable[[TV, SynapseRequest], Awaitable[None]]:
"""Wraps a request handler method with exception handling.
Also does the wrapping with request.processing as per wrap_async_request_handler.
@ -141,20 +149,26 @@ def wrap_html_request_handler(h):
async def wrapped_request_handler(self, request):
try:
return await h(self, request)
await h(self, request)
except Exception:
f = failure.Failure()
return _return_html_error(f, request)
return_html_error(f, request, HTML_ERROR_TEMPLATE)
return wrap_async_request_handler(wrapped_request_handler)
def _return_html_error(f, request):
"""Sends an HTML error page corresponding to the given failure
def return_html_error(
f: failure.Failure, request: Request, error_template: Union[str, jinja2.Template],
) -> None:
"""Sends an HTML error page corresponding to the given failure.
Handles RedirectException and other CodeMessageExceptions (such as SynapseError)
Args:
f (twisted.python.failure.Failure):
request (twisted.web.server.Request):
f: the error to report
request: the failing request
error_template: the HTML template. Can be either a string (with `{code}`,
`{msg}` placeholders), or a jinja2 template
"""
if f.check(CodeMessageException):
cme = f.value
@ -174,7 +188,7 @@ def _return_html_error(f, request):
exc_info=(f.type, f.value, f.getTracebackObject()),
)
else:
code = http.client.INTERNAL_SERVER_ERROR
code = http.HTTPStatus.INTERNAL_SERVER_ERROR
msg = "Internal server error"
logger.error(
@ -183,11 +197,16 @@ def _return_html_error(f, request):
exc_info=(f.type, f.value, f.getTracebackObject()),
)
body = HTML_ERROR_TEMPLATE.format(code=code, msg=html.escape(msg)).encode("utf-8")
if isinstance(error_template, str):
body = error_template.format(code=code, msg=html.escape(msg))
else:
body = error_template.render(code=code, msg=msg)
body_bytes = body.encode("utf-8")
request.setResponseCode(code)
request.setHeader(b"Content-Type", b"text/html; charset=utf-8")
request.setHeader(b"Content-Length", b"%i" % (len(body),))
request.write(body)
request.setHeader(b"Content-Length", b"%i" % (len(body_bytes),))
request.write(body_bytes)
finish_request(request)

26
synapse/rest/saml2/response_resource.py
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@ -13,12 +13,10 @@
# 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.
from twisted.python import failure
from synapse.http.server import (
DirectServeResource,
finish_request,
wrap_html_request_handler,
)
from synapse.api.errors import SynapseError
from synapse.http.server import DirectServeResource, return_html_error
class SAML2ResponseResource(DirectServeResource):
@ -28,20 +26,22 @@ class SAML2ResponseResource(DirectServeResource):
def __init__(self, hs):
super().__init__()
self._error_html_content = hs.config.saml2_error_html_content
self._saml_handler = hs.get_saml_handler()
self._error_html_template = hs.config.saml2.saml2_error_html_template
async def _async_render_GET(self, request):
# We're not expecting any GET request on that resource if everything goes right,
# but some IdPs sometimes end up responding with a 302 redirect on this endpoint.
# In this case, just tell the user that something went wrong and they should
# try to authenticate again.
request.setResponseCode(400)
request.setHeader(b"Content-Type", b"text/html; charset=utf-8")
request.setHeader(b"Content-Length", b"%d" % (len(self._error_html_content),))
request.write(self._error_html_content.encode("utf8"))
finish_request(request)
f = failure.Failure(
SynapseError(400, "Unexpected GET request on /saml2/authn_response")
)
return_html_error(f, request, self._error_html_template)
@wrap_html_request_handler
async def _async_render_POST(self, request):
return await self._saml_handler.handle_saml_response(request)
try:
await self._saml_handler.handle_saml_response(request)
except Exception:
f = failure.Failure()
return_html_error(f, request, self._error_html_template)

1
tox.ini
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@ -193,6 +193,7 @@ commands = mypy \
synapse/handlers/saml_handler.py \
synapse/handlers/sync.py \
synapse/handlers/ui_auth \
synapse/http/server.py \
synapse/http/site.py \
synapse/logging/ \
synapse/metrics \