# sslutil.py - SSL handling for mercurial

#

# Copyright 2005, 2006, 2007, 2008 Matt Mackall <mpm@selenic.com>

# Copyright 2006, 2007 Alexis S. L. Carvalho <alexis@cecm.usp.br>

# Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com>

#

# 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)

def _determinecertoptions(ui, host):

    """Determine certificate options for a connections.

    Returns a tuple of (cert_reqs, ca_certs).

    """

    # If a host key fingerprint is on file, it is the only thing that matters

    # and CA certs don't come into play.

    hostfingerprint = ui.config('hostfingerprints', host)

    if hostfingerprint:

        return ssl.CERT_NONE, None

    # The code below sets up CA verification arguments. If --insecure is

    # used, we don't take CAs into consideration, so return early.

    if ui.insecureconnections:

        return ssl.CERT_NONE, None

    cacerts = ui.config('web', 'cacerts')

    # If a value is set in the config, validate against a path and load

    # and require those certs.

    if cacerts:

        cacerts = util.expandpath(cacerts)

        if not os.path.exists(cacerts):

            raise error.Abort(_('could not find web.cacerts: %s') % cacerts)

        return ssl.CERT_REQUIRED, cacerts

    # No CAs in config. See if we can load defaults.

    cacerts = _defaultcacerts()

    # We found an alternate CA bundle to use. Load it.

    if cacerts:

        ui.debug('using %s to enable OS X system CA\n' % cacerts)

        ui.setconfig('web', 'cacerts', cacerts, 'defaultcacerts')

        return ssl.CERT_REQUIRED, cacerts

    # FUTURE this can disappear once wrapsocket() is secure by default.

    if _canloaddefaultcerts:

        return ssl.CERT_REQUIRED, None

    return ssl.CERT_NONE, None

def wrapsocket(sock, keyfile, certfile, ui, serverhostname=None):

    """Add SSL/TLS to a socket.

    This is a glorified wrapper for ``ssl.wrap_socket()``. It makes sane

    choices based on what security options are available.

    In addition to the arguments supported by ``ssl.wrap_socket``, we allow

    the following additional arguments:

    * serverhostname - The expected hostname of the remote server. If the

      server (and client) support SNI, this tells the server which certificate

      to use.

    """

    if not serverhostname:

        raise error.Abort('serverhostname argument is required')

    cert_reqs, ca_certs = _determinecertoptions(ui, serverhostname)

    # 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

    # This still works on our fake SSLContext.

    sslcontext.verify_mode = cert_reqs

    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)

    if ca_certs is not None:

        sslcontext.load_verify_locations(cafile=ca_certs)

        caloaded = True

    else:

        # This is a no-op on old Python.

        sslcontext.load_default_certs()

        caloaded = _canloaddefaultcerts

    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'))

    sslsocket._hgstate = {

        'caloaded': caloaded,

        'hostname': serverhostname,

        'ui': ui,

    }

    return sslsocket

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 default CA certificates or None."""

    if _plainapplepython():

        dummycert = os.path.join(os.path.dirname(__file__), 'dummycert.pem')

        if os.path.exists(dummycert):

            return dummycert

    return None

def validatesocket(sock, strict=False):

    """Validate a socket meets security requiremnets.

    The passed socket must have been created with ``wrapsocket()``.

    """

    host = sock._hgstate['hostname']

    ui = sock._hgstate['ui']

    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)

    # If a certificate fingerprint is pinned, use it and only it to

    # validate the remote cert.

    hostfingerprints = ui.configlist('hostfingerprints', 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'))

        ui.debug('%s certificate matched fingerprint %s\n' %

                 (host, nicefingerprint))

        return

    # If insecure connections were explicitly requested via --insecure,

    # print a warning and do no verification.

    #

    # It may seem odd that this is checked *after* host fingerprint pinning.

    # This is for backwards compatibility (for now). The message is also

    # the same as below for BC.

    if ui.insecureconnections:

        ui.warn(_('warning: %s certificate with fingerprint %s not '

                  'verified (check hostfingerprints or web.cacerts '

                  'config setting)\n') %

                (host, nicefingerprint))

        return

    if not sock._hgstate['caloaded']:

        if strict:

            raise error.Abort(_('%s certificate with fingerprint %s not '

                                'verified') % (host, nicefingerprint),

                              hint=_('check hostfingerprints or '

                                     'web.cacerts config setting'))

        else:

            ui.warn(_('warning: %s certificate with fingerprint %s '

                      'not verified (check hostfingerprints or '

                      'web.cacerts config setting)\n') %

                    (host, nicefingerprint))

        return

    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)