pyopenssl.py

"""
SSL with SNI_-support for Python 2. Follow these instructions if you would
like to verify SSL certificates in Python 2. Note, the default libraries do
*not* do certificate checking; you need to do additional work to validate
certificates yourself.

This needs the following packages installed:

* pyOpenSSL (tested with 16.0.0)
* cryptography (minimum 1.3.4, from pyopenssl)
* idna (minimum 2.0, from cryptography)

However, pyopenssl depends on cryptography, which depends on idna, so while we
use all three directly here we end up having relatively few packages required.

You can install them with the following command:

    pip install pyopenssl cryptography idna

To activate certificate checking, call
:func:`~urllib3.contrib.pyopenssl.inject_into_urllib3` from your Python code
before you begin making HTTP requests. This can be done in a ``sitecustomize``
module, or at any other time before your application begins using ``urllib3``,
like this::

    try:
        import urllib3.contrib.pyopenssl
        urllib3.contrib.pyopenssl.inject_into_urllib3()
    except ImportError:
        pass

Now you can use :mod:`urllib3` as you normally would, and it will support SNI
when the required modules are installed.

Activating this module also has the positive side effect of disabling SSL/TLS
compression in Python 2 (see `CRIME attack`_).

If you want to configure the default list of supported cipher suites, you can
set the ``urllib3.contrib.pyopenssl.DEFAULT_SSL_CIPHER_LIST`` variable.

.. _sni: https://en.wikipedia.org/wiki/Server_Name_Indication
.. _crime attack: https://en.wikipedia.org/wiki/CRIME_(security_exploit)
"""
from __future__ import absolute_import

import OpenSSL.SSL
from cryptography import x509
from cryptography.hazmat.backends.openssl import backend as openssl_backend
from cryptography.hazmat.backends.openssl.x509 import _Certificate
try:
    from cryptography.x509 import UnsupportedExtension
except ImportError:
    # UnsupportedExtension is gone in cryptography >= 2.1.0
    class UnsupportedExtension(Exception):
        pass

from socket import timeout, error as SocketError
from io import BytesIO

try:  # Platform-specific: Python 2
    from socket import _fileobject
except ImportError:  # Platform-specific: Python 3
    _fileobject = None
    from ..packages.backports.makefile import backport_makefile

import logging
import ssl
from ..packages import six
import sys

from .. import util

__all__ = ['inject_into_urllib3', 'extract_from_urllib3']

# SNI always works.
HAS_SNI = True

# Map from urllib3 to PyOpenSSL compatible parameter-values.
_openssl_versions = {
    ssl.PROTOCOL_SSLv23: OpenSSL.SSL.SSLv23_METHOD,
    ssl.PROTOCOL_TLSv1: OpenSSL.SSL.TLSv1_METHOD,
}

if hasattr(ssl, 'PROTOCOL_TLSv1_1') and hasattr(OpenSSL.SSL, 'TLSv1_1_METHOD'):
    _openssl_versions[ssl.PROTOCOL_TLSv1_1] = OpenSSL.SSL.TLSv1_1_METHOD

if hasattr(ssl, 'PROTOCOL_TLSv1_2') and hasattr(OpenSSL.SSL, 'TLSv1_2_METHOD'):
    _openssl_versions[ssl.PROTOCOL_TLSv1_2] = OpenSSL.SSL.TLSv1_2_METHOD

try:
    _openssl_versions.update({ssl.PROTOCOL_SSLv3: OpenSSL.SSL.SSLv3_METHOD})
except AttributeError:
    pass

_stdlib_to_openssl_verify = {
    ssl.CERT_NONE: OpenSSL.SSL.VERIFY_NONE,
    ssl.CERT_OPTIONAL: OpenSSL.SSL.VERIFY_PEER,
    ssl.CERT_REQUIRED:
        OpenSSL.SSL.VERIFY_PEER + OpenSSL.SSL.VERIFY_FAIL_IF_NO_PEER_CERT,
}
_openssl_to_stdlib_verify = dict(
    (v, k) for k, v in _stdlib_to_openssl_verify.items()
)

# OpenSSL will only write 16K at a time
SSL_WRITE_BLOCKSIZE = 16384

orig_util_HAS_SNI = util.HAS_SNI
orig_util_SSLContext = util.ssl_.SSLContext


log = logging.getLogger(__name__)


def inject_into_urllib3():
    'Monkey-patch urllib3 with PyOpenSSL-backed SSL-support.'

    _validate_dependencies_met()

    util.ssl_.SSLContext = PyOpenSSLContext
    util.HAS_SNI = HAS_SNI
    util.ssl_.HAS_SNI = HAS_SNI
    util.IS_PYOPENSSL = True
    util.ssl_.IS_PYOPENSSL = True


def extract_from_urllib3():
    'Undo monkey-patching by :func:`inject_into_urllib3`.'

    util.ssl_.SSLContext = orig_util_SSLContext
    util.HAS_SNI = orig_util_HAS_SNI
    util.ssl_.HAS_SNI = orig_util_HAS_SNI
    util.IS_PYOPENSSL = False
    util.ssl_.IS_PYOPENSSL = False


def _validate_dependencies_met():
    """
    Verifies that PyOpenSSL's package-level dependencies have been met.
    Throws `ImportError` if they are not met.
    """
    # Method added in `cryptography==1.1`; not available in older versions
    from cryptography.x509.extensions import Extensions
    if getattr(Extensions, "get_extension_for_class", None) is None:
        raise ImportError("'cryptography' module missing required functionality.  "
                          "Try upgrading to v1.3.4 or newer.")

    # pyOpenSSL 0.14 and above use cryptography for OpenSSL bindings. The _x509
    # attribute is only present on those versions.
    from OpenSSL.crypto import X509
    x509 = X509()
    if getattr(x509, "_x509", None) is None:
        raise ImportError("'pyOpenSSL' module missing required functionality. "
                          "Try upgrading to v0.14 or newer.")


def _dnsname_to_stdlib(name):
    """
    Converts a dNSName SubjectAlternativeName field to the form used by the
    standard library on the given Python version.

    Cryptography produces a dNSName as a unicode string that was idna-decoded
    from ASCII bytes. We need to idna-encode that string to get it back, and
    then on Python 3 we also need to convert to unicode via UTF-8 (the stdlib
    uses PyUnicode_FromStringAndSize on it, which decodes via UTF-8).

    If the name cannot be idna-encoded then we return None signalling that
    the name given should be skipped.
    """
    def idna_encode(name):
        """
        Borrowed wholesale from the Python Cryptography Project. It turns out
        that we can't just safely call `idna.encode`: it can explode for
        wildcard names. This avoids that problem.
        """
        import idna

        try:
            for prefix in [u'*.', u'.']:
                if name.startswith(prefix):
                    name = name[len(prefix):]
                    return prefix.encode('ascii') + idna.encode(name)
            return idna.encode(name)
        except idna.core.IDNAError:
            return None

    name = idna_encode(name)
    if name is None:
        return None
    elif sys.version_info >= (3, 0):
        name = name.decode('utf-8')
    return name


def get_subj_alt_name(peer_cert):
    """
    Given an PyOpenSSL certificate, provides all the subject alternative names.
    """
    # Pass the cert to cryptography, which has much better APIs for this.
    if hasattr(peer_cert, "to_cryptography"):
        cert = peer_cert.to_cryptography()
    else:
        # This is technically using private APIs, but should work across all
        # relevant versions before PyOpenSSL got a proper API for this.
        cert = _Certificate(openssl_backend, peer_cert._x509)

    # We want to find the SAN extension. Ask Cryptography to locate it (it's
    # faster than looping in Python)
    try:
        ext = cert.extensions.get_extension_for_class(
            x509.SubjectAlternativeName
        ).value
    except x509.ExtensionNotFound:
        # No such extension, return the empty list.
        return []
    except (x509.DuplicateExtension, UnsupportedExtension,
            x509.UnsupportedGeneralNameType, UnicodeError) as e:
        # A problem has been found with the quality of the certificate. Assume
        # no SAN field is present.
        log.warning(
            "A problem was encountered with the certificate that prevented "
            "urllib3 from finding the SubjectAlternativeName field. This can "
            "affect certificate validation. The error was %s",
            e,
        )
        return []

    # We want to return dNSName and iPAddress fields. We need to cast the IPs
    # back to strings because the match_hostname function wants them as
    # strings.
    # Sadly the DNS names need to be idna encoded and then, on Python 3, UTF-8
    # decoded. This is pretty frustrating, but that's what the standard library
    # does with certificates, and so we need to attempt to do the same.
    # We also want to skip over names which cannot be idna encoded.
    names = [
        ('DNS', name) for name in map(_dnsname_to_stdlib, ext.get_values_for_type(x509.DNSName))
        if name is not None
    ]
    names.extend(
        ('IP Address', str(name))
        for name in ext.get_values_for_type(x509.IPAddress)
    )

    return names


class WrappedSocket(object):
    '''API-compatibility wrapper for Python OpenSSL's Connection-class.

    Note: _makefile_refs, _drop() and _reuse() are needed for the garbage
    collector of pypy.
    '''

    def __init__(self, connection, socket, suppress_ragged_eofs=True):
        self.connection = connection
        self.socket = socket
        self.suppress_ragged_eofs = suppress_ragged_eofs
        self._makefile_refs = 0
        self._closed = False

    def fileno(self):
        return self.socket.fileno()

    # Copy-pasted from Python 3.5 source code
    def _decref_socketios(self):
        if self._makefile_refs > 0:
            self._makefile_refs -= 1
        if self._closed:
            self.close()

    def recv(self, *args, **kwargs):
        try:
            data = self.connection.recv(*args, **kwargs)
        except OpenSSL.SSL.SysCallError as e:
            if self.suppress_ragged_eofs and e.args == (-1, 'Unexpected EOF'):
                return b''
            else:
                raise SocketError(str(e))
        except OpenSSL.SSL.ZeroReturnError:
            if self.connection.get_shutdown() == OpenSSL.SSL.RECEIVED_SHUTDOWN:
                return b''
            else:
                raise
        except OpenSSL.SSL.WantReadError:
            if not util.wait_for_read(self.socket, self.socket.gettimeout()):
                raise timeout('The read operation timed out')
            else:
                return self.recv(*args, **kwargs)
        else:
            return data

    def recv_into(self, *args, **kwargs):
        try:
            return self.connection.recv_into(*args, **kwargs)
        except OpenSSL.SSL.SysCallError as e:
            if self.suppress_ragged_eofs and e.args == (-1, 'Unexpected EOF'):
                return 0
            else:
                raise SocketError(str(e))
        except OpenSSL.SSL.ZeroReturnError:
            if self.connection.get_shutdown() == OpenSSL.SSL.RECEIVED_SHUTDOWN:
                return 0
            else:
                raise
        except OpenSSL.SSL.WantReadError:
            if not util.wait_for_read(self.socket, self.socket.gettimeout()):
                raise timeout('The read operation timed out')
            else:
                return self.recv_into(*args, **kwargs)

    def settimeout(self, timeout):
        return self.socket.settimeout(timeout)

    def _send_until_done(self, data):
        while True:
            try:
                return self.connection.send(data)
            except OpenSSL.SSL.WantWriteError:
                if not util.wait_for_write(self.socket, self.socket.gettimeout()):
                    raise timeout()
                continue
            except OpenSSL.SSL.SysCallError as e:
                raise SocketError(str(e))

    def sendall(self, data):
        total_sent = 0
        while total_sent < len(data):
            sent = self._send_until_done(data[total_sent:total_sent + SSL_WRITE_BLOCKSIZE])
            total_sent += sent

    def shutdown(self):
        # FIXME rethrow compatible exceptions should we ever use this
        self.connection.shutdown()

    def close(self):
        if self._makefile_refs < 1:
            try:
                self._closed = True
                return self.connection.close()
            except OpenSSL.SSL.Error:
                return
        else:
            self._makefile_refs -= 1

    def getpeercert(self, binary_form=False):
        x509 = self.connection.get_peer_certificate()

        if not x509:
            return x509

        if binary_form:
            return OpenSSL.crypto.dump_certificate(
                OpenSSL.crypto.FILETYPE_ASN1,
                x509)

        return {
            'subject': (
                (('commonName', x509.get_subject().CN),),
            ),
            'subjectAltName': get_subj_alt_name(x509)
        }

    def version(self):
        return self.connection.get_protocol_version_name()

    def _reuse(self):
        self._makefile_refs += 1

    def _drop(self):
        if self._makefile_refs < 1:
            self.close()
        else:
            self._makefile_refs -= 1


if _fileobject:  # Platform-specific: Python 2
    def makefile(self, mode, bufsize=-1):
        self._makefile_refs += 1
        return _fileobject(self, mode, bufsize, close=True)
else:  # Platform-specific: Python 3
    makefile = backport_makefile

WrappedSocket.makefile = makefile


class PyOpenSSLContext(object):
    """
    I am a wrapper class for the PyOpenSSL ``Context`` object. I am responsible
    for translating the interface of the standard library ``SSLContext`` object
    to calls into PyOpenSSL.
    """
    def __init__(self, protocol):
        self.protocol = _openssl_versions[protocol]
        self._ctx = OpenSSL.SSL.Context(self.protocol)
        self._options = 0
        self.check_hostname = False

    @property
    def options(self):
        return self._options

    @options.setter
    def options(self, value):
        self._options = value
        self._ctx.set_options(value)

    @property
    def verify_mode(self):
        return _openssl_to_stdlib_verify[self._ctx.get_verify_mode()]

    @verify_mode.setter
    def verify_mode(self, value):
        self._ctx.set_verify(
            _stdlib_to_openssl_verify[value],
            _verify_callback
        )

    def set_default_verify_paths(self):
        self._ctx.set_default_verify_paths()

    def set_ciphers(self, ciphers):
        if isinstance(ciphers, six.text_type):
            ciphers = ciphers.encode('utf-8')
        self._ctx.set_cipher_list(ciphers)

    def load_verify_locations(self, cafile=None, capath=None, cadata=None):
        if cafile is not None:
            cafile = cafile.encode('utf-8')
        if capath is not None:
            capath = capath.encode('utf-8')
        self._ctx.load_verify_locations(cafile, capath)
        if cadata is not None:
            self._ctx.load_verify_locations(BytesIO(cadata))

    def load_cert_chain(self, certfile, keyfile=None, password=None):
        self._ctx.use_certificate_chain_file(certfile)
        if password is not None:
            self._ctx.set_passwd_cb(lambda max_length, prompt_twice, userdata: password)
        self._ctx.use_privatekey_file(keyfile or certfile)

    def wrap_socket(self, sock, server_side=False,
                    do_handshake_on_connect=True, suppress_ragged_eofs=True,
                    server_hostname=None):
        cnx = OpenSSL.SSL.Connection(self._ctx, sock)

        if isinstance(server_hostname, six.text_type):  # Platform-specific: Python 3
            server_hostname = server_hostname.encode('utf-8')

        if server_hostname is not None:
            cnx.set_tlsext_host_name(server_hostname)

        cnx.set_connect_state()

        while True:
            try:
                cnx.do_handshake()
            except OpenSSL.SSL.WantReadError:
                if not util.wait_for_read(sock, sock.gettimeout()):
                    raise timeout('select timed out')
                continue
            except OpenSSL.SSL.Error as e:
                raise ssl.SSLError('bad handshake: %r' % e)
            break

        return WrappedSocket(cnx, sock)


def _verify_callback(cnx, x509, err_no, err_depth, return_code):
    return err_no == 0