sydent/sydent/http/federation_tls_options.py

# Copyright 2019 New Vector 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.

from OpenSSL import SSL
from twisted.internet import ssl
from twisted.internet.abstract import isIPAddress, isIPv6Address
from twisted.internet.interfaces import IOpenSSLClientConnectionCreator
from zope.interface import implementer


def _tolerateErrors(wrapped):
    """
    Wrap up an info_callback for pyOpenSSL so that if something goes wrong
    the error is immediately logged and the connection is dropped if possible.
    This is a copy of twisted.internet._sslverify._tolerateErrors. For
    documentation, see the twisted documentation.
    """

    def infoCallback(connection, where, ret):
        try:
            return wrapped(connection, where, ret)
        except:  # noqa: E722, taken from the twisted implementation
            f = Failure()
            logger.exception("Error during info_callback")
            connection.get_app_data().failVerification(f)

    return infoCallback


def _idnaBytes(text):
    """
    Convert some text typed by a human into some ASCII bytes. This is a
    copy of twisted.internet._idna._idnaBytes. For documentation, see the
    twisted documentation.
    """
    try:
        import idna
    except ImportError:
        return text.encode("idna")
    else:
        return idna.encode(text)


@implementer(IOpenSSLClientConnectionCreator)
class ClientTLSOptions:
    """
    Client creator for TLS without certificate identity verification. This is a
    copy of twisted.internet._sslverify.ClientTLSOptions with the identity
    verification left out. For documentation, see the twisted documentation.
    """

    def __init__(self, hostname, ctx):
        self._ctx = ctx

        if isIPAddress(hostname) or isIPv6Address(hostname):
            self._hostnameBytes = hostname.encode("ascii")
            self._sendSNI = False
        else:
            self._hostnameBytes = _idnaBytes(hostname)
            self._sendSNI = True

        ctx.set_info_callback(_tolerateErrors(self._identityVerifyingInfoCallback))

    def clientConnectionForTLS(self, tlsProtocol):
        context = self._ctx
        connection = SSL.Connection(context, None)
        connection.set_app_data(tlsProtocol)
        return connection

    def _identityVerifyingInfoCallback(self, connection, where, ret):
        # Literal IPv4 and IPv6 addresses are not permitted
        # as host names according to the RFCs
        if where & SSL.SSL_CB_HANDSHAKE_START and self._sendSNI:
            connection.set_tlsext_host_name(self._hostnameBytes)


class ClientTLSOptionsFactory:
    """Factory for Twisted ClientTLSOptions that are used to make connections
    to remote servers for federation."""

    def __init__(self, verify_requests):
        if verify_requests:
            self._options = ssl.CertificateOptions(trustRoot=ssl.platformTrust())
        else:
            self._options = ssl.CertificateOptions()

    def get_options(self, host):
        # Use _makeContext so that we get a fresh OpenSSL CTX each time.
        return ClientTLSOptions(host, self._options._makeContext())