ssl: load CA certificates from system's store by default on Python 2.7.9

This will make it easy to manage in-house CA certificates, which are often
used in corporate environment and installed into the Windows' certs store.

Unlike Apple python, the dummycert trick isn't necessary on Python 2.7.9.
The default web.cacerts will be set as follows:

  environment    web.cacerts  behavior
  -------------  -----------  -----------------------------------------
  Apple Python   dummycert    fall back to system's store
  Python 2.7.8   '!'          never use CA certs (show warning instead)
  Python 2.7.9+  None         load CA certs from system's store

mercurial/sslutil.py

@@ -1,222 +1,231 b''
 # 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.
 import os, sys
 
 from mercurial import util
 from mercurial.i18n import _
+
+_canloaddefaultcerts = False
 try:
     # avoid using deprecated/broken FakeSocket in python 2.6
     import ssl
     CERT_REQUIRED = ssl.CERT_REQUIRED
     try:
         ssl_context = ssl.SSLContext
+        _canloaddefaultcerts = util.safehasattr(ssl_context,
+                                                'load_default_certs')
 
         def ssl_wrap_socket(sock, keyfile, certfile, cert_reqs=ssl.CERT_NONE,
                             ca_certs=None, serverhostname=None):
             # Allow any version of SSL starting with TLSv1 and
             # up. Note that specifying TLSv1 here prohibits use of
             # newer standards (like TLSv1_2), so this is the right way
             # to do this. Note that in the future it'd be better to
             # support using ssl.create_default_context(), which sets
             # up a bunch of things in smart ways (strong ciphers,
             # protocol versions, etc) and is upgraded by Python
             # maintainers for us, but that breaks too many things to
             # do it in a hurry.
             sslcontext = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
             sslcontext.options &= ssl.OP_NO_SSLv2 & ssl.OP_NO_SSLv3
             if certfile is not None:
                 sslcontext.load_cert_chain(certfile, keyfile)
             sslcontext.verify_mode = cert_reqs
             if ca_certs is not None:
                 sslcontext.load_verify_locations(cafile=ca_certs)
+            elif _canloaddefaultcerts:
+                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 util.Abort(_('ssl connection failed'))
             return sslsocket
     except AttributeError:
         def ssl_wrap_socket(sock, keyfile, certfile, cert_reqs=ssl.CERT_NONE,
                             ca_certs=None, serverhostname=None):
             sslsocket = ssl.wrap_socket(sock, keyfile, certfile,
                                         cert_reqs=cert_reqs, ca_certs=ca_certs,
                                         ssl_version=ssl.PROTOCOL_TLSv1)
             # check if wrap_socket failed silently because socket had been
             # closed
             # - see http://bugs.python.org/issue13721
             if not sslsocket.cipher():
                 raise util.Abort(_('ssl connection failed'))
             return sslsocket
 except ImportError:
     CERT_REQUIRED = 2
 
     import socket, httplib
 
     def ssl_wrap_socket(sock, keyfile, certfile, cert_reqs=CERT_REQUIRED,
                         ca_certs=None, serverhostname=None):
         if not util.safehasattr(socket, 'ssl'):
             raise util.Abort(_('Python SSL support not found'))
         if ca_certs:
             raise util.Abort(_(
                 'certificate checking requires Python 2.6'))
 
         ssl = socket.ssl(sock, keyfile, certfile)
         return httplib.FakeSocket(sock, ssl)
 
 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.
 #
 # We COMPLETELY ignore CERT_REQUIRED on Python <= 2.5, as it's totally
 # busted on those versions.
 
 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():
         return False
     exe = (sys.executable or '').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 = {}
     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 util.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': 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')
         hostfingerprint = self.ui.config('hostfingerprints', host)
         if not getattr(sock, 'getpeercert', False): # python 2.5 ?
             if hostfingerprint:
                 raise util.Abort(_("host fingerprint for %s can't be "
                                    "verified (Python too old)") % host)
             if strict:
                 raise util.Abort(_("certificate for %s can't be verified "
                                    "(Python too old)") % host)
             if self.ui.configbool('ui', 'reportoldssl', True):
                 self.ui.warn(_("warning: certificate for %s can't be verified "
                                "(Python too old)\n") % host)
             return
 
         if not sock.cipher(): # work around http://bugs.python.org/issue13721
             raise util.Abort(_('%s ssl connection error') % host)
         try:
             peercert = sock.getpeercert(True)
             peercert2 = sock.getpeercert()
         except AttributeError:
             raise util.Abort(_('%s ssl connection error') % host)
 
         if not peercert:
             raise util.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 hostfingerprint:
             if peerfingerprint.lower() != \
                     hostfingerprint.replace(':', '').lower():
                 raise util.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 util.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 util.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))