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improve tls handling, separate set_server and set_server_tls

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This commit is contained in:
Maximilian Hils 2016-05-02 16:51:19 -07:00
parent 7f894c131b
commit 626f7e1017
3 changed files with 76 additions and 73 deletions
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11
mitmproxy/protocol/base.py
View File

@ -133,24 +133,15 @@ class ServerConnectionMixin(object):
"The proxy shall not connect to itself.".format(repr(address))
)
def set_server(self, address, server_tls=None, sni=None):
def set_server(self, address):
"""
Sets a new server address. If there is an existing connection, it will be closed.
Raises:
~mitmproxy.exceptions.ProtocolException:
if ``server_tls`` is ``True``, but there was no TLS layer on the
protocol stack which could have processed this.
"""
if self.server_conn:
self.disconnect()
self.log("Set new server address: " + repr(address), "debug")
self.server_conn.address = address
self.__check_self_connect()
if server_tls:
raise ProtocolException(
"Cannot upgrade to TLS, no TLS layer on the protocol stack."
)
def disconnect(self):
"""

12
mitmproxy/protocol/http.py
View File

@ -120,7 +120,7 @@ class UpstreamConnectLayer(Layer):
if address != self.server_conn.via.address:
self.ctx.set_server(address)
def set_server(self, address, server_tls=None, sni=None):
def set_server(self, address):
if self.ctx.server_conn:
self.ctx.disconnect()
address = tcp.Address.wrap(address)
@ -128,11 +128,6 @@ class UpstreamConnectLayer(Layer):
self.connect_request.port = address.port
self.server_conn.address = address
if server_tls:
raise ProtocolException(
"Cannot upgrade to TLS, no TLS layer on the protocol stack."
)
class HttpLayer(Layer):
@ -355,8 +350,9 @@ class HttpLayer(Layer):
if self.mode == "regular" or self.mode == "transparent":
# If there's an existing connection that doesn't match our expectations, kill it.
if address != self.server_conn.address or tls != self.server_conn.tls_established:
self.set_server(address, tls, address.host)
if address != self.server_conn.address or tls != self.server_tls:
self.set_server(address)
self.set_server_tls(tls, address.host)
# Establish connection is neccessary.
if not self.server_conn:
self.connect()

126
mitmproxy/protocol/tls.py
View File

@ -308,6 +308,15 @@ class TlsClientHello(object):
class TlsLayer(Layer):
"""
The TLS layer implements transparent TLS connections.
It exposes the following API to child layers:
- :py:meth:`set_server_tls` to modify TLS settings for the server connection.
- :py:attr:`server_tls`, :py:attr:`server_sni` as read-only attributes describing the current TLS settings for
the server connection.
"""
def __init__(self, ctx, client_tls, server_tls):
self.client_sni = None
@ -318,40 +327,46 @@ class TlsLayer(Layer):
self._client_tls = client_tls
self._server_tls = server_tls
self._sni_from_server_change = None
self._custom_server_sni = None
def __call__(self):
"""
The strategy for establishing SSL is as follows:
The strategy for establishing TLS is as follows:
First, we determine whether we need the server cert to establish ssl with the client.
If so, we first connect to the server and then to the client.
If not, we only connect to the client and do the server_ssl lazily on a Connect message.
If not, we only connect to the client and do the server handshake lazily.
An additional complexity is that establish ssl with the server may require a SNI value from
the client. In an ideal world, we'd do the following:
1. Start the SSL handshake with the client
2. Check if the client sends a SNI.
3. Pause the client handshake, establish SSL with the server.
4. Finish the client handshake with the certificate from the server.
There's just one issue: We cannot get a callback from OpenSSL if the client doesn't send a SNI. :(
Thus, we manually peek into the connection and parse the ClientHello message to obtain both SNI and ALPN values.
Further notes:
- OpenSSL 1.0.2 introduces a callback that would help here:
https://www.openssl.org/docs/ssl/SSL_CTX_set_cert_cb.html
- The original mitmproxy issue is https://github.com/mitmproxy/mitmproxy/issues/427
An additional complexity is that we need to mirror SNI and ALPN from the client when connecting to the server.
We manually peek into the connection and parse the ClientHello message to obtain these values.
"""
if self._client_tls:
self._parse_client_hello()
# Peek into the connection, read the initial client hello and parse it to obtain SNI and ALPN values.
try:
parsed = TlsClientHello.from_client_conn(self.client_conn)
self.client_sni = parsed.client_sni
self.client_alpn_protocols = parsed.client_alpn_protocols
self.client_ciphers = parsed.client_cipher_suites
except TlsProtocolException as e:
self.log("Cannot parse Client Hello: %s" % repr(e), "error")
# Do we need the server certificate to establish TLS with the client?
# First, this requires that we have TLS on both the client and the server connection.
# Second, this must be disabled if the user specified --no-upstream-cert
# Third, if the client sends a SNI value, we can be reasonably sure that this is the actual target host.
client_tls_requires_server_cert = (
self._client_tls and self._server_tls and not self.config.no_upstream_cert and not self.client_sni
# Third, we need to connect if add_upstream_certs_to_client_chain is on.
# Fourth, we need to connect if the client wants to negotiate an alternate protocol using ALPN.
# Fifth, we need to connect if the client did not send a SNI value.
client_tls_requires_server_connection = (
self._client_tls and self._server_tls
and not self.config.no_upstream_cert
and
(
self.config.add_upstream_certs_to_client_chain
or self.client_alpn_protocols
or not self.client_sni
)
)
if client_tls_requires_server_cert:
if client_tls_requires_server_connection:
self._establish_tls_with_client_and_server()
elif self._client_tls:
self._establish_tls_with_client()
@ -369,47 +384,48 @@ class TlsLayer(Layer):
else:
return "TlsLayer(inactive)"
def _parse_client_hello(self):
"""
Peek into the connection, read the initial client hello and parse it to obtain ALPN values.
"""
try:
parsed = TlsClientHello.from_client_conn(self.client_conn)
self.client_sni = parsed.client_sni
self.client_alpn_protocols = parsed.client_alpn_protocols
self.client_ciphers = parsed.client_cipher_suites
except TlsProtocolException as e:
self.log("Cannot parse Client Hello: %s" % repr(e), "error")
def connect(self):
if not self.server_conn:
self.ctx.connect()
if self._server_tls and not self.server_conn.tls_established:
self._establish_tls_with_server()
def set_server(self, address, server_tls=None, sni=None):
if server_tls is not None:
self._sni_from_server_change = sni
self._server_tls = server_tls
self.ctx.set_server(address, None, None)
def set_server_tls(self, server_tls, sni=None):
"""
Set the TLS settings for the next server connection that will be established.
This function will not alter an existing connection.
Args:
server_tls: Shall we establish TLS with the server?
sni: ``bytes`` for a custom SNI value,
``None`` for the client SNI value,
``False`` if no SNI value should be sent.
"""
self._server_tls = server_tls
self._custom_server_sni = sni
@property
def sni_for_server_connection(self):
if self._sni_from_server_change is False:
def server_tls(self):
"""
``True``, if the next server connection that will be established should be upgraded to TLS.
"""
return self._server_tls
@property
def server_sni(self):
"""
The Server Name Indication we want to send with the next server TLS handshake.
"""
if self._custom_server_sni is False:
return None
else:
return self._sni_from_server_change or self.client_sni
return self._custom_server_sni or self.client_sni
@property
def alpn_for_client_connection(self):
return self.server_conn.get_alpn_proto_negotiated()
def __alpn_select_callback(self, conn_, options):
"""
Once the client signals the alternate protocols it supports,
we reconnect upstream with the same list and pass the server's choice down to the client.
"""
# This gets triggered if we haven't established an upstream connection yet.
default_alpn = b'http/1.1'
# alpn_preference = b'h2'
@ -424,12 +440,12 @@ class TlsLayer(Layer):
return choice
def _establish_tls_with_client_and_server(self):
# If establishing TLS with the server fails, we try to establish TLS with the client nonetheless
# to send an error message over TLS.
try:
self.ctx.connect()
self._establish_tls_with_server()
except Exception:
# If establishing TLS with the server fails, we try to establish TLS with the client nonetheless
# to send an error message over TLS.
try:
self._establish_tls_with_client()
except:
@ -499,7 +515,7 @@ class TlsLayer(Layer):
self.server_conn.establish_ssl(
self.config.clientcerts,
self.sni_for_server_connection,
self.server_sni,
method=self.config.openssl_method_server,
options=self.config.openssl_options_server,
verify_options=self.config.openssl_verification_mode_server,
@ -526,7 +542,7 @@ class TlsLayer(Layer):
TlsProtocolException,
TlsProtocolException("Cannot establish TLS with {address} (sni: {sni}): {e}".format(
address=repr(self.server_conn.address),
sni=self.sni_for_server_connection,
sni=self.server_sni,
e=repr(e),
)),
sys.exc_info()[2]
@ -536,7 +552,7 @@ class TlsLayer(Layer):
TlsProtocolException,
TlsProtocolException("Cannot establish TLS with {address} (sni: {sni}): {e}".format(
address=repr(self.server_conn.address),
sni=self.sni_for_server_connection,
sni=self.server_sni,
e=repr(e),
)),
sys.exc_info()[2]
@ -573,11 +589,11 @@ class TlsLayer(Layer):
# Also add SNI values.
if self.client_sni:
sans.add(self.client_sni)
if self._sni_from_server_change:
sans.add(self._sni_from_server_change)
if self._custom_server_sni:
sans.add(self._custom_server_sni)
# Some applications don't consider the CN and expect the hostname to be in the SANs.
# For example, Thunderbird 38 will display a warning if the remote host is only the CN.
# RFC 2818: If a subjectAltName extension of type dNSName is present, that MUST be used as the identity.
# In other words, the Common Name is irrelevant then.
if host:
sans.add(host)
return self.config.certstore.get_cert(host, list(sans))