mercurial/sslutil.py

sslutil: fall back to commonName when no dNSName in subjectAltName (issue2798)

Any entries in subjectAltName would prevent fallback to using commonName, but
RFC 2818 says:

    If a subjectAltName extension of type dNSName is present, that MUST
    be used as the identity. Otherwise, the (most specific) Common Name
    field in the Subject field of the certificate MUST be used.

We now only consider dNSNames in subjectAltName.

(dNSName is known as 'DNS' in OpenSSL/Python.)

# 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

from mercurial import util
from mercurial.i18n import _
try:
    # avoid using deprecated/broken FakeSocket in python 2.6
    import ssl
    ssl_wrap_socket = ssl.wrap_socket
    CERT_REQUIRED = ssl.CERT_REQUIRED
except ImportError:
    CERT_REQUIRED = 2

    import socket, httplib

    def ssl_wrap_socket(sock, key_file, cert_file,
                        cert_reqs=CERT_REQUIRED, ca_certs=None):
        if ca_certs:
            raise util.Abort(_(
                'certificate checking requires Python 2.6'))

        ssl = socket.ssl(sock, key_file, cert_file)
        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 sslkwargs(ui, host):
    cacerts = ui.config('web', 'cacerts')
    hostfingerprint = ui.config('hostfingerprints', host)
    if cacerts and not hostfingerprint:
        cacerts = util.expandpath(cacerts)
        if not os.path.exists(cacerts):
            raise util.Abort(_('could not find web.cacerts: %s') % cacerts)
        return {'ca_certs': cacerts,
                'cert_reqs': CERT_REQUIRED,
                }
    return {}

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

    def __call__(self, sock):
        host = self.host
        cacerts = self.ui.config('web', 'cacerts')
        hostfingerprint = self.ui.config('hostfingerprints', host)
        if cacerts and not hostfingerprint:
            msg = _verifycert(sock.getpeercert(), host)
            if msg:
                raise util.Abort(_('%s certificate error: %s '
                                   '(use --insecure to connect '
                                   'insecurely)') % (host, msg))
            self.ui.debug('%s certificate successfully verified\n' % host)
        else:
            if getattr(sock, 'getpeercert', False):
                peercert = sock.getpeercert(True)
                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(_('invalid certificate for %s '
                                           'with fingerprint %s') %
                                         (host, nicefingerprint))
                    self.ui.debug('%s certificate matched fingerprint %s\n' %
                                  (host, nicefingerprint))
                else:
                    self.ui.warn(_('warning: %s certificate '
                                   'with fingerprint %s not verified '
                                   '(check hostfingerprints or web.cacerts '
                                   'config setting)\n') %
                                 (host, nicefingerprint))
            else: # python 2.5 ?
                if hostfingerprint:
                    raise util.Abort(_('no certificate for %s with '
                                       'configured hostfingerprint') % host)
                self.ui.warn(_('warning: %s certificate not verified '
                               '(check web.cacerts config setting)\n') %
                             host)