view mercurial/sslutil.py @ 28651:4827d07073e6

sslutil: always use SSLContext

Now that we have a fake SSLContext instance, we can unify the code
paths for wrapping sockets to always use the SSLContext APIs.

Because this is security code, I've retained the try..except to
make the diff easier to read. It will be removed in the next patch.

I took the liberty of updating the inline docs about supported
protocols and how the constants work because this stuff is important
and needs to be explicitly documented.

# sslutil.py - SSL handling for mercurial
#
# Copyright 2005, 2006, 2007, 2008 Matt Mackall <[e-mail]>
# Copyright 2006, 2007 Alexis S. L. Carvalho <[e-mail]>
# Copyright 2006 Vadim Gelfer <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import os
import ssl
import sys

from .i18n import _
from . import (
    error,
    util,
)

# Python 2.7.9+ overhauled the built-in SSL/TLS features of Python. It added
# support for TLS 1.1, TLS 1.2, SNI, system CA stores, etc. These features are
# all exposed via the "ssl" module.
#
# Depending on the version of Python being used, SSL/TLS support is either
# modern/secure or legacy/insecure. Many operations in this module have
# separate code paths depending on support in Python.

hassni = getattr(ssl, 'HAS_SNI', False)

try:
    OP_NO_SSLv2 = ssl.OP_NO_SSLv2
    OP_NO_SSLv3 = ssl.OP_NO_SSLv3
except AttributeError:
    OP_NO_SSLv2 = 0x1000000
    OP_NO_SSLv3 = 0x2000000

try:
    # ssl.SSLContext was added in 2.7.9 and presence indicates modern
    # SSL/TLS features are available.
    SSLContext = ssl.SSLContext
    modernssl = True
    _canloaddefaultcerts = util.safehasattr(SSLContext, 'load_default_certs')
except AttributeError:
    modernssl = False
    _canloaddefaultcerts = False

    # We implement SSLContext using the interface from the standard library.
    class SSLContext(object):
        # ssl.wrap_socket gained the "ciphers" named argument in 2.7.
        _supportsciphers = sys.version_info >= (2, 7)

        def __init__(self, protocol):
            # From the public interface of SSLContext
            self.protocol = protocol
            self.check_hostname = False
            self.options = 0
            self.verify_mode = ssl.CERT_NONE

            # Used by our implementation.
            self._certfile = None
            self._keyfile = None
            self._certpassword = None
            self._cacerts = None
            self._ciphers = None

        def load_cert_chain(self, certfile, keyfile=None, password=None):
            self._certfile = certfile
            self._keyfile = keyfile
            self._certpassword = password

        def load_default_certs(self, purpose=None):
            pass

        def load_verify_locations(self, cafile=None, capath=None, cadata=None):
            if capath:
                raise error.Abort('capath not supported')
            if cadata:
                raise error.Abort('cadata not supported')

            self._cacerts = cafile

        def set_ciphers(self, ciphers):
            if not self._supportsciphers:
                raise error.Abort('setting ciphers not supported')

            self._ciphers = ciphers

        def wrap_socket(self, socket, server_hostname=None, server_side=False):
            # server_hostname is unique to SSLContext.wrap_socket and is used
            # for SNI in that context. So there's nothing for us to do with it
            # in this legacy code since we don't support SNI.

            args = {
                'keyfile': self._keyfile,
                'certfile': self._certfile,
                'server_side': server_side,
                'cert_reqs': self.verify_mode,
                'ssl_version': self.protocol,
                'ca_certs': self._cacerts,
            }

            if self._supportsciphers:
                args['ciphers'] = self._ciphers

            return ssl.wrap_socket(socket, **args)

try:
    def wrapsocket(sock, keyfile, certfile, ui, cert_reqs=ssl.CERT_NONE,
                   ca_certs=None, serverhostname=None):
        # Despite its name, PROTOCOL_SSLv23 selects the highest protocol
        # that both ends support, including TLS protocols. On legacy stacks,
        # the highest it likely goes in TLS 1.0. On modern stacks, it can
        # support TLS 1.2.
        #
        # The PROTOCOL_TLSv* constants select a specific TLS version
        # only (as opposed to multiple versions). So the method for
        # supporting multiple TLS versions is to use PROTOCOL_SSLv23 and
        # disable protocols via SSLContext.options and OP_NO_* constants.
        # However, SSLContext.options doesn't work unless we have the
        # full/real SSLContext available to us.
        #
        # SSLv2 and SSLv3 are broken. We ban them outright.
        if modernssl:
            protocol = ssl.PROTOCOL_SSLv23
        else:
            protocol = ssl.PROTOCOL_TLSv1

        # TODO use ssl.create_default_context() on modernssl.
        sslcontext = SSLContext(protocol)

        # This is a no-op on old Python.
        sslcontext.options |= OP_NO_SSLv2 | OP_NO_SSLv3

        if certfile is not None:
            def password():
                f = keyfile or certfile
                return ui.getpass(_('passphrase for %s: ') % f, '')
            sslcontext.load_cert_chain(certfile, keyfile, password)
        sslcontext.verify_mode = cert_reqs
        if ca_certs is not None:
            sslcontext.load_verify_locations(cafile=ca_certs)
        else:
            # This is a no-op on old Python.
            sslcontext.load_default_certs()

        sslsocket = sslcontext.wrap_socket(sock, server_hostname=serverhostname)
        # check if wrap_socket failed silently because socket had been
        # closed
        # - see http://bugs.python.org/issue13721
        if not sslsocket.cipher():
            raise error.Abort(_('ssl connection failed'))
        return sslsocket
except AttributeError:
    raise util.Abort('this should not happen')

def _verifycert(cert, hostname):
    '''Verify that cert (in socket.getpeercert() format) matches hostname.
    CRLs is not handled.

    Returns error message if any problems are found and None on success.
    '''
    if not cert:
        return _('no certificate received')
    dnsname = hostname.lower()
    def matchdnsname(certname):
        return (certname == dnsname or
                '.' in dnsname and certname == '*.' + dnsname.split('.', 1)[1])

    san = cert.get('subjectAltName', [])
    if san:
        certnames = [value.lower() for key, value in san if key == 'DNS']
        for name in certnames:
            if matchdnsname(name):
                return None
        if certnames:
            return _('certificate is for %s') % ', '.join(certnames)

    # subject is only checked when subjectAltName is empty
    for s in cert.get('subject', []):
        key, value = s[0]
        if key == 'commonName':
            try:
                # 'subject' entries are unicode
                certname = value.lower().encode('ascii')
            except UnicodeEncodeError:
                return _('IDN in certificate not supported')
            if matchdnsname(certname):
                return None
            return _('certificate is for %s') % certname
    return _('no commonName or subjectAltName found in certificate')


# CERT_REQUIRED means fetch the cert from the server all the time AND
# validate it against the CA store provided in web.cacerts.

def _plainapplepython():
    """return true if this seems to be a pure Apple Python that
    * is unfrozen and presumably has the whole mercurial module in the file
      system
    * presumably is an Apple Python that uses Apple OpenSSL which has patches
      for using system certificate store CAs in addition to the provided
      cacerts file
    """
    if sys.platform != 'darwin' or util.mainfrozen() or not sys.executable:
        return False
    exe = os.path.realpath(sys.executable).lower()
    return (exe.startswith('/usr/bin/python') or
            exe.startswith('/system/library/frameworks/python.framework/'))

def _defaultcacerts():
    """return path to CA certificates; None for system's store; ! to disable"""
    if _plainapplepython():
        dummycert = os.path.join(os.path.dirname(__file__), 'dummycert.pem')
        if os.path.exists(dummycert):
            return dummycert
    if _canloaddefaultcerts:
        return None
    return '!'

def sslkwargs(ui, host):
    kws = {'ui': ui}
    hostfingerprint = ui.config('hostfingerprints', host)
    if hostfingerprint:
        return kws
    cacerts = ui.config('web', 'cacerts')
    if cacerts == '!':
        pass
    elif cacerts:
        cacerts = util.expandpath(cacerts)
        if not os.path.exists(cacerts):
            raise error.Abort(_('could not find web.cacerts: %s') % cacerts)
    else:
        cacerts = _defaultcacerts()
        if cacerts and cacerts != '!':
            ui.debug('using %s to enable OS X system CA\n' % cacerts)
        ui.setconfig('web', 'cacerts', cacerts, 'defaultcacerts')
    if cacerts != '!':
        kws.update({'ca_certs': cacerts,
                    'cert_reqs': ssl.CERT_REQUIRED,
                    })
    return kws

class validator(object):
    def __init__(self, ui, host):
        self.ui = ui
        self.host = host

    def __call__(self, sock, strict=False):
        host = self.host
        cacerts = self.ui.config('web', 'cacerts')
        hostfingerprints = self.ui.configlist('hostfingerprints', host)

        if not sock.cipher(): # work around http://bugs.python.org/issue13721
            raise error.Abort(_('%s ssl connection error') % host)
        try:
            peercert = sock.getpeercert(True)
            peercert2 = sock.getpeercert()
        except AttributeError:
            raise error.Abort(_('%s ssl connection error') % host)

        if not peercert:
            raise error.Abort(_('%s certificate error: '
                               'no certificate received') % host)
        peerfingerprint = util.sha1(peercert).hexdigest()
        nicefingerprint = ":".join([peerfingerprint[x:x + 2]
            for x in xrange(0, len(peerfingerprint), 2)])
        if hostfingerprints:
            fingerprintmatch = False
            for hostfingerprint in hostfingerprints:
                if peerfingerprint.lower() == \
                        hostfingerprint.replace(':', '').lower():
                    fingerprintmatch = True
                    break
            if not fingerprintmatch:
                raise error.Abort(_('certificate for %s has unexpected '
                                   'fingerprint %s') % (host, nicefingerprint),
                                 hint=_('check hostfingerprint configuration'))
            self.ui.debug('%s certificate matched fingerprint %s\n' %
                          (host, nicefingerprint))
        elif cacerts != '!':
            msg = _verifycert(peercert2, host)
            if msg:
                raise error.Abort(_('%s certificate error: %s') % (host, msg),
                                 hint=_('configure hostfingerprint %s or use '
                                        '--insecure to connect insecurely') %
                                      nicefingerprint)
            self.ui.debug('%s certificate successfully verified\n' % host)
        elif strict:
            raise error.Abort(_('%s certificate with fingerprint %s not '
                               'verified') % (host, nicefingerprint),
                             hint=_('check hostfingerprints or web.cacerts '
                                     'config setting'))
        else:
            self.ui.warn(_('warning: %s certificate with fingerprint %s not '
                           'verified (check hostfingerprints or web.cacerts '
                           'config setting)\n') %
                         (host, nicefingerprint))