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pydtls/dtls/sslconnection.py

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# SSL connection: state and behavior associated with the connection between
# the OpenSSL library and an individual peer.
# Copyright 2012 Ray Brown
#
# 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
#
# The License is also distributed with this work in the file named "LICENSE."
#
# 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.
"""SSL Connection
This module encapsulates the state and behavior associated with the connection
between the OpenSSL library and an individual peer when using the DTLS
protocol. It defines the application side of the interface of a client with a
DTLS server, and of a server with a DTLS client.
Classes:
SSLConnection -- DTLS peer association
Integer constants:
PROTOCOL_DTLSv1
The cert group must coincide in meaning and value with the one of the standard
library's ssl module, since its values can be passed to this module.
CERT_NONE
CERT_OPTIONAL
CERT_REQUIRED
"""
import errno
import socket
import hmac
import datetime
from logging import getLogger
from os import urandom
from select import select
from weakref import proxy
from err import openssl_error, InvalidSocketError
from err import raise_ssl_error
from err import SSL_ERROR_WANT_READ, SSL_ERROR_SYSCALL
from err import ERR_COOKIE_MISMATCH, ERR_NO_CERTS
from err import ERR_NO_CIPHER, ERR_HANDSHAKE_TIMEOUT, ERR_PORT_UNREACHABLE
from err import ERR_READ_TIMEOUT, ERR_WRITE_TIMEOUT
from x509 import _X509, decode_cert
from tlock import tlock_init
from openssl import *
from util import _Rsrc, _BIO
_logger = getLogger(__name__)
PROTOCOL_DTLSv1 = 256
CERT_NONE = 0
CERT_OPTIONAL = 1
CERT_REQUIRED = 2
#
# One-time global OpenSSL library initialization
#
SSL_library_init()
SSL_load_error_strings()
tlock_init()
DTLS_OPENSSL_VERSION_NUMBER = SSLeay()
DTLS_OPENSSL_VERSION = SSLeay_version(SSLEAY_VERSION)
DTLS_OPENSSL_VERSION_INFO = (
DTLS_OPENSSL_VERSION_NUMBER >> 28 & 0xFF, # major
DTLS_OPENSSL_VERSION_NUMBER >> 20 & 0xFF, # minor
DTLS_OPENSSL_VERSION_NUMBER >> 12 & 0xFF, # fix
DTLS_OPENSSL_VERSION_NUMBER >> 4 & 0xFF, # patch
DTLS_OPENSSL_VERSION_NUMBER & 0xF) # status
class _CTX(_Rsrc):
"""SSL_CTX wrapper"""
def __init__(self, value):
super(_CTX, self).__init__(value)
def __del__(self):
_logger.debug("Freeing SSL CTX: %d", self.raw)
SSL_CTX_free(self._value)
self._value = None
class _SSL(_Rsrc):
"""SSL structure wrapper"""
def __init__(self, value):
super(_SSL, self).__init__(value)
def __del__(self):
_logger.debug("Freeing SSL: %d", self.raw)
SSL_free(self._value)
self._value = None
class _CallbackProxy(object):
"""Callback gateway to an SSLConnection object
This class forms a weak connection between a callback method and
an SSLConnection object. It can be passed as a callback callable
without creating a strong reference through bound methods of
the SSLConnection.
"""
def __init__(self, cbm):
self.ssl_connection = proxy(cbm.im_self)
self.ssl_func = cbm.im_func
def __call__(self, *args, **kwargs):
return self.ssl_func(self.ssl_connection, *args, **kwargs)
class SSLConnection(object):
"""DTLS peer association
This class associates two DTLS peer instances, wrapping OpenSSL library
state including SSL (struct ssl_st), SSL_CTX, and BIO instances.
"""
_rnd_key = urandom(16)
def _init_server(self, peer_address):
if self._sock.type != socket.SOCK_DGRAM:
raise InvalidSocketError("sock must be of type SOCK_DGRAM")
self._wbio = _BIO(BIO_new_dgram(self._sock.fileno(), BIO_NOCLOSE))
if peer_address:
# Connect directly to this client peer, bypassing the demux
rsock = self._sock
BIO_dgram_set_connected(self._wbio.value, peer_address)
else:
from demux import UDPDemux
self._udp_demux = UDPDemux(self._sock)
rsock = self._udp_demux.get_connection(None)
if rsock is self._sock:
self._rbio = self._wbio
else:
self._rsock = rsock
self._rbio = _BIO(BIO_new_dgram(self._rsock.fileno(), BIO_NOCLOSE))
self._ctx = _CTX(SSL_CTX_new(DTLSv1_server_method()))
SSL_CTX_set_session_cache_mode(self._ctx.value, SSL_SESS_CACHE_OFF)
if self._cert_reqs == CERT_NONE:
verify_mode = SSL_VERIFY_NONE
elif self._cert_reqs == CERT_OPTIONAL:
verify_mode = SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE
else:
verify_mode = SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE | \
SSL_VERIFY_FAIL_IF_NO_PEER_CERT
self._config_ssl_ctx(verify_mode)
if not peer_address:
# Configure UDP listening socket
self._listening = False
self._listening_peer_address = None
self._pending_peer_address = None
self._cb_keepalive = SSL_CTX_set_cookie_cb(
self._ctx.value,
_CallbackProxy(self._generate_cookie_cb),
_CallbackProxy(self._verify_cookie_cb))
self._ssl = _SSL(SSL_new(self._ctx.value))
SSL_set_accept_state(self._ssl.value)
if peer_address and self._do_handshake_on_connect:
return lambda: self.do_handshake()
def _init_client(self, peer_address):
if self._sock.type != socket.SOCK_DGRAM:
raise InvalidSocketError("sock must be of type SOCK_DGRAM")
self._wbio = _BIO(BIO_new_dgram(self._sock.fileno(), BIO_NOCLOSE))
self._rbio = self._wbio
self._ctx = _CTX(SSL_CTX_new(DTLSv1_client_method()))
if self._cert_reqs == CERT_NONE:
verify_mode = SSL_VERIFY_NONE
else:
verify_mode = SSL_VERIFY_PEER
self._config_ssl_ctx(verify_mode)
self._ssl = _SSL(SSL_new(self._ctx.value))
SSL_set_connect_state(self._ssl.value)
if peer_address:
return lambda: self.connect(peer_address)
def _config_ssl_ctx(self, verify_mode):
SSL_CTX_set_verify(self._ctx.value, verify_mode)
SSL_CTX_set_read_ahead(self._ctx.value, 1)
# Compression occurs at the stream layer now, leading to datagram
# corruption when packet loss occurs
SSL_CTX_set_options(self._ctx.value, SSL_OP_NO_COMPRESSION)
if self._certfile:
SSL_CTX_use_certificate_chain_file(self._ctx.value, self._certfile)
if self._keyfile:
SSL_CTX_use_PrivateKey_file(self._ctx.value, self._keyfile,
SSL_FILE_TYPE_PEM)
if self._ca_certs:
SSL_CTX_load_verify_locations(self._ctx.value, self._ca_certs, None)
if self._ciphers:
try:
SSL_CTX_set_cipher_list(self._ctx.value, self._ciphers)
except openssl_error() as err:
raise_ssl_error(ERR_NO_CIPHER, err)
def _copy_server(self):
source = self._sock
self._udp_demux = source._udp_demux
rsock = self._udp_demux.get_connection(source._pending_peer_address)
self._ctx = source._ctx
self._ssl = source._ssl
new_source_wbio = _BIO(BIO_new_dgram(source._sock.fileno(),
BIO_NOCLOSE))
if hasattr(source, "_rsock"):
self._sock = source._sock
self._rsock = rsock
self._wbio = _BIO(BIO_new_dgram(self._sock.fileno(), BIO_NOCLOSE))
self._rbio = _BIO(BIO_new_dgram(rsock.fileno(), BIO_NOCLOSE))
new_source_rbio = _BIO(BIO_new_dgram(source._rsock.fileno(),
BIO_NOCLOSE))
BIO_dgram_set_peer(self._wbio.value, source._pending_peer_address)
else:
self._sock = rsock
self._wbio = _BIO(BIO_new_dgram(self._sock.fileno(), BIO_NOCLOSE))
self._rbio = self._wbio
new_source_rbio = new_source_wbio
BIO_dgram_set_connected(self._wbio.value,
source._pending_peer_address)
source._ssl = _SSL(SSL_new(self._ctx.value))
SSL_set_accept_state(source._ssl.value)
source._rbio = new_source_rbio
source._wbio = new_source_wbio
SSL_set_bio(source._ssl.value,
new_source_rbio.value,
new_source_wbio.value)
new_source_rbio.disown()
new_source_wbio.disown()
def _reconnect_unwrapped(self):
source = self._sock
self._sock = source._wsock
self._udp_demux = source._demux
self._rsock = source._rsock
self._ctx = source._ctx
self._wbio = _BIO(BIO_new_dgram(self._sock.fileno(), BIO_NOCLOSE))
self._rbio = _BIO(BIO_new_dgram(self._rsock.fileno(), BIO_NOCLOSE))
BIO_dgram_set_peer(self._wbio.value, source._peer_address)
self._ssl = _SSL(SSL_new(self._ctx.value))
SSL_set_accept_state(self._ssl.value)
if self._do_handshake_on_connect:
return lambda: self.do_handshake()
def _check_nbio(self):
timeout = self._sock.gettimeout()
if self._wbio_nb != timeout is not None:
BIO_set_nbio(self._wbio.value, timeout is not None)
self._wbio_nb = timeout is not None
if self._wbio is not self._rbio:
timeout = self._rsock.gettimeout()
if self._rbio_nb != timeout is not None:
BIO_set_nbio(self._rbio.value, timeout is not None)
self._rbio_nb = timeout is not None
return timeout # read channel timeout
def _wrap_socket_library_call(self, call, timeout_error):
timeout_sec_start = timeout_sec = self._check_nbio()
# Pass the call if the socket is blocking or non-blocking
if not timeout_sec: # None (blocking) or zero (non-blocking)
return call()
start_time = datetime.datetime.now()
read_sock = self.get_socket(True)
need_select = False
while timeout_sec > 0:
if need_select:
if not select([read_sock], [], [], timeout_sec)[0]:
break
timeout_sec = timeout_sec_start - \
(datetime.datetime.now() - start_time).total_seconds()
try:
return call()
except openssl_error() as err:
if err.ssl_error == SSL_ERROR_WANT_READ:
need_select = True
continue
raise
raise_ssl_error(timeout_error)
def _get_cookie(self, ssl):
assert self._listening
assert self._ssl.raw == ssl.raw
if self._listening_peer_address:
peer_address = self._listening_peer_address
else:
peer_address = BIO_dgram_get_peer(self._rbio.value)
cookie_hmac = hmac.new(self._rnd_key, str(peer_address))
return cookie_hmac.digest()
def _generate_cookie_cb(self, ssl):
return self._get_cookie(ssl)
def _verify_cookie_cb(self, ssl, cookie):
if self._get_cookie(ssl) != cookie:
raise Exception("DTLS cookie mismatch")
def __init__(self, sock, keyfile=None, certfile=None,
server_side=False, cert_reqs=CERT_NONE,
ssl_version=PROTOCOL_DTLSv1, ca_certs=None,
do_handshake_on_connect=True,
suppress_ragged_eofs=True, ciphers=None):
"""Constructor
Arguments:
these arguments match the ones of the SSLSocket class in the
standard library's ssl module
"""
if keyfile and not certfile or certfile and not keyfile:
raise_ssl_error(ERR_BOTH_KEY_CERT_FILES)
if server_side and not keyfile:
raise_ssl_error(ERR_BOTH_KEY_CERT_FILES_SVR)
if cert_reqs != CERT_NONE and not ca_certs:
raise_ssl_error(ERR_NO_CERTS)
if not ciphers:
ciphers = "DEFAULT"
self._sock = sock
self._keyfile = keyfile
self._certfile = certfile
self._cert_reqs = cert_reqs
self._ca_certs = ca_certs
self._do_handshake_on_connect = do_handshake_on_connect
self._suppress_ragged_eofs = suppress_ragged_eofs
self._ciphers = ciphers
self._handshake_done = False
self._wbio_nb = self._rbio_nb = False
if isinstance(sock, SSLConnection):
post_init = self._copy_server()
elif isinstance(sock, _UnwrappedSocket):
post_init = self._reconnect_unwrapped()
else:
try:
peer_address = sock.getpeername()
except socket.error:
peer_address = None
if server_side:
post_init = self._init_server(peer_address)
else:
post_init = self._init_client(peer_address)
SSL_set_bio(self._ssl.value, self._rbio.value, self._wbio.value)
self._rbio.disown()
self._wbio.disown()
if post_init:
post_init()
def get_socket(self, inbound):
"""Retrieve a socket used by this connection
When inbound is True, then the socket from which this connection reads
data is retrieved. Otherwise the socket to which this connection writes
data is retrieved.
Read and write sockets differ depending on whether this is a server- or
a client-side connection, and on whether a routing demux is in use.
"""
if inbound and hasattr(self, "_rsock"):
return self._rsock
return self._sock
def listen(self):
"""Server-side cookie exchange
This method reads datagrams from the socket and initiates cookie
exchange, upon whose successful conclusion one can then proceed to
the accept method. Alternatively, accept can be called directly, in
which case it will call this method. In order to prevent denial-of-
service attacks, only a small, constant set of computing resources
are used during the listen phase.
On some platforms, listen must be called so that packets will be
forwarded to accepted connections. Doing so is therefore recommened
in all cases for portable code.
Return value: a peer address if a datagram from a new peer was
encountered, None if a datagram for a known peer was forwarded
"""
if not hasattr(self, "_listening"):
raise InvalidSocketError("listen called on non-listening socket")
self._pending_peer_address = None
try:
peer_address = self._udp_demux.service()
except socket.timeout:
peer_address = None
except socket.error as sock_err:
if sock_err.errno != errno.EWOULDBLOCK:
_logger.exception("Unexpected socket error in listen")
raise
peer_address = None
if not peer_address:
_logger.debug("Listen returning without peer")
return
# The demux advises that a datagram from a new peer may have arrived
if type(peer_address) is tuple:
# For this type of demux, the write BIO must be pointed at the peer
BIO_dgram_set_peer(self._wbio.value, peer_address)
self._udp_demux.forward()
self._listening_peer_address = peer_address
self._check_nbio()
self._listening = True
try:
_logger.debug("Invoking DTLSv1_listen for ssl: %d",
self._ssl.raw)
dtls_peer_address = DTLSv1_listen(self._ssl.value)
except openssl_error() as err:
if err.ssl_error == SSL_ERROR_WANT_READ:
# This method must be called again to forward the next datagram
_logger.debug("DTLSv1_listen must be resumed")
return
elif err.errqueue and err.errqueue[0][0] == ERR_COOKIE_MISMATCH:
_logger.debug("Mismatching cookie received; aborting handshake")
return
_logger.exception("Unexpected error in DTLSv1_listen")
raise
finally:
self._listening = False
self._listening_peer_address = None
if type(peer_address) is tuple:
_logger.debug("New local peer: %s", dtls_peer_address)
self._pending_peer_address = peer_address
else:
self._pending_peer_address = dtls_peer_address
_logger.debug("New peer: %s", self._pending_peer_address)
return self._pending_peer_address
def accept(self):
"""Server-side UDP connection establishment
This method returns a server-side SSLConnection object, connected to
that peer most recently returned from the listen method and not yet
connected. If there is no such peer, then the listen method is invoked.
Return value: SSLConnection connected to a new peer, None if packet
forwarding only to an existing peer occurred.
"""
if not self._pending_peer_address:
if not self.listen():
_logger.debug("Accept returning without connection")
return
new_conn = SSLConnection(self, self._keyfile, self._certfile, True,
self._cert_reqs, PROTOCOL_DTLSv1,
self._ca_certs, self._do_handshake_on_connect,
self._suppress_ragged_eofs, self._ciphers)
new_peer = self._pending_peer_address
self._pending_peer_address = None
if self._do_handshake_on_connect:
# Note that since that connection's socket was just created in its
# constructor, the following operation must be blocking; hence
# handshake-on-connect can only be used with a routing demux if
# listen is serviced by a separate application thread, or else we
# will hang in this call
new_conn.do_handshake()
_logger.debug("Accept returning new connection for new peer")
return new_conn, new_peer
def connect(self, peer_address):
"""Client-side UDP connection establishment
This method connects this object's underlying socket. It subsequently
performs a handshake if do_handshake_on_connect was set during
initialization.
Arguments:
peer_address - address tuple of server peer
"""
self._sock.connect(peer_address)
peer_address = self._sock.getpeername() # substituted host addrinfo
BIO_dgram_set_connected(self._wbio.value, peer_address)
assert self._wbio is self._rbio
if self._do_handshake_on_connect:
self.do_handshake()
def do_handshake(self):
"""Perform a handshake with the peer
This method forces an explicit handshake to be performed with either
the client or server peer.
"""
_logger.debug("Initiating handshake...")
try:
self._wrap_socket_library_call(
lambda: SSL_do_handshake(self._ssl.value),
ERR_HANDSHAKE_TIMEOUT)
except openssl_error() as err:
if err.ssl_error == SSL_ERROR_SYSCALL and err.result == -1:
raise_ssl_error(ERR_PORT_UNREACHABLE, err)
raise
self._handshake_done = True
_logger.debug("...completed handshake")
def read(self, len=1024):
"""Read data from connection
Read up to len bytes and return them.
Arguments:
len -- maximum number of bytes to read
Return value:
string containing read bytes
"""
return self._wrap_socket_library_call(
lambda: SSL_read(self._ssl.value, len), ERR_READ_TIMEOUT)
def write(self, data):
"""Write data to connection
Write data as string of bytes.
Arguments:
data -- buffer containing data to be written
Return value:
number of bytes actually transmitted
"""
return self._wrap_socket_library_call(
lambda: SSL_write(self._ssl.value, data), ERR_WRITE_TIMEOUT)
def shutdown(self):
"""Shut down the DTLS connection
This method attemps to complete a bidirectional shutdown between
peers. For non-blocking sockets, it should be called repeatedly until
it no longer raises continuation request exceptions.
"""
if hasattr(self, "_listening"):
# Listening server-side sockets cannot be shut down
return
try:
self._wrap_socket_library_call(
lambda: SSL_shutdown(self._ssl.value), ERR_READ_TIMEOUT)
except openssl_error() as err:
if err.result == 0:
# close-notify alert was just sent; wait for same from peer
# Note: while it might seem wise to suppress further read-aheads
# with SSL_set_read_ahead here, doing so causes a shutdown
# failure (ret: -1, SSL_ERROR_SYSCALL) on the DTLS shutdown
# initiator side. And test_starttls does pass.
self._wrap_socket_library_call(
lambda: SSL_shutdown(self._ssl.value), ERR_READ_TIMEOUT)
else:
raise
if hasattr(self, "_rsock"):
# Return wrapped connected server socket (non-listening)
return _UnwrappedSocket(self._sock, self._rsock, self._udp_demux,
self._ctx,
BIO_dgram_get_peer(self._wbio.value))
# Return unwrapped client-side socket or unwrapped server-side socket
# for single-socket servers
return self._sock
def getpeercert(self, binary_form=False):
"""Retrieve the peer's certificate
When binary form is requested, the peer's DER-encoded certficate is
returned if it was transmitted during the handshake.
When binary form is not requested, and the peer's certificate has been
validated, then a certificate dictionary is returned. If the certificate
was not validated, an empty dictionary is returned.
In all cases, None is returned if no certificate was received from the
peer.
"""
try:
peer_cert = _X509(SSL_get_peer_certificate(self._ssl.value))
except openssl_error():
return
if binary_form:
return i2d_X509(peer_cert.value)
if self._cert_reqs == CERT_NONE:
return {}
return decode_cert(peer_cert)
peer_certificate = getpeercert # compatibility with _ssl call interface
def cipher(self):
"""Retrieve information about the current cipher
Return a triple consisting of cipher name, SSL protocol version defining
its use, and the number of secret bits. Return None if handshaking
has not been completed.
"""
if not self._handshake_done:
return
current_cipher = SSL_get_current_cipher(self._ssl.value)
cipher_name = SSL_CIPHER_get_name(current_cipher)
cipher_version = SSL_CIPHER_get_version(current_cipher)
cipher_bits = SSL_CIPHER_get_bits(current_cipher)
return cipher_name, cipher_version, cipher_bits
def pending(self):
"""Retrieve number of buffered bytes
Return the number of bytes that have been read from the socket and
buffered by this connection. Return 0 if no bytes have been buffered.
"""
return SSL_pending(self._ssl.value)
def get_timeout(self):
"""Retrieve the retransmission timedelta
Since datagrams are subject to packet loss, DTLS will perform
packet retransmission if a response is not received after a certain
time interval during the handshaking phase. When using non-blocking
sockets, the application must call back after that time interval to
allow for the retransmission to occur. This method returns the
timedelta after which to perform the call to handle_timeout, or None
if no such callback is needed given the current handshake state.
"""
return DTLSv1_get_timeout(self._ssl.value)
def handle_timeout(self):
"""Perform datagram retransmission, if required
This method should be called after the timedelta retrieved from
get_timeout has expired, and no datagrams were received in the
meantime. If datagrams were received, a new timeout needs to be
requested.
Return value:
True -- retransmissions were performed successfully
False -- a timeout was not in effect or had not yet expired
Exceptions:
Raised when retransmissions fail or too many timeouts occur.
"""
return DTLSv1_handle_timeout(self._ssl.value)
class _UnwrappedSocket(socket.socket):
"""Unwrapped server-side socket
Depending on UDP demux implementation, there may not be single socket
that can be used for both reading and writing to the client socket with
which it is associated. An object of this type is therefore returned from
the SSLSocket's unwrap method to allow for unencrypted communication over
the established channels, including the demux.
"""
def __init__(self, wsock, rsock, demux, ctx, peer_address):
socket.socket.__init__(self, _sock=rsock._sock)
for attr in "send", "sendto", "sendall":
try:
delattr(self, attr)
except AttributeError:
pass
self._wsock = wsock
self._rsock = rsock # continue to reference to hold in demux map
self._demux = demux
self._ctx = ctx
self._peer_address = peer_address
def send(self, data, flags=0):
__doc__ = self._wsock.send.__doc__
return self._wsock.sendto(data, flags, self._peer_address)
def sendto(self, data, flags_or_addr, addr=None):
__doc__ = self._wsock.sendto.__doc__
return self._wsock.sendto(data, flags_or_addr, addr)
def sendall(self, data, flags=0):
__doc__ = self._wsock.sendall.__doc__
amount = len(data)
count = 0
while (count < amount):
v = self.send(data[count:], flags)
count += v
return amount
def getpeername(self):
__doc__ = self._wsock.getpeername.__doc__
return self._peer_address
def connect(self, addr):
__doc__ = self._wsock.connect.__doc__
raise ValueError("Cannot connect already connected unwrapped socket")
connect_ex = connect
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