# 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 _hostsettings(ui, hostname):

    """Obtain security settings for a hostname.

    Returns a dict of settings relevant to that hostname.

    """

    s = {

        # Whether we should attempt to load default/available CA certs

        # if an explicit ``cafile`` is not defined.

        'allowloaddefaultcerts': True,

        # List of 2-tuple of (hash algorithm, hash).

        'certfingerprints': [],

        # Path to file containing concatenated CA certs. Used by

        # SSLContext.load_verify_locations().

        'cafile': None,

        # Whether certificate verification should be disabled.

        'disablecertverification': False,

        # Whether the legacy [hostfingerprints] section has data for this host.

        'legacyfingerprint': False,

        # ssl.CERT_* constant used by SSLContext.verify_mode.

        'verifymode': None,

    }

    # Look for fingerprints in [hostsecurity] section. Value is a list

    # of <alg>:<fingerprint> strings.

    fingerprints = ui.configlist('hostsecurity', '%s:fingerprints' % hostname,

                                 [])

    for fingerprint in fingerprints:

        if not (fingerprint.startswith(('sha1:', 'sha256:', 'sha512:'))):

            raise error.Abort(_('invalid fingerprint for %s: %s') % (

                                hostname, fingerprint),

                              hint=_('must begin with "sha1:", "sha256:", '

                                     'or "sha512:"'))

        alg, fingerprint = fingerprint.split(':', 1)

        fingerprint = fingerprint.replace(':', '').lower()

        s['certfingerprints'].append((alg, fingerprint))

    # Fingerprints from [hostfingerprints] are always SHA-1.

    for fingerprint in ui.configlist('hostfingerprints', hostname, []):

        fingerprint = fingerprint.replace(':', '').lower()

        s['certfingerprints'].append(('sha1', fingerprint))

        s['legacyfingerprint'] = True

    # If a host cert fingerprint is defined, it is the only thing that

    # matters. No need to validate CA certs.

    if s['certfingerprints']:

        s['verifymode'] = ssl.CERT_NONE

    # If --insecure is used, don't take CAs into consideration.

    elif ui.insecureconnections:

        s['disablecertverification'] = True

        s['verifymode'] = ssl.CERT_NONE

    if ui.configbool('devel', 'disableloaddefaultcerts'):

        s['allowloaddefaultcerts'] = False

    # If both fingerprints and a per-host ca file are specified, issue a warning

    # because users should not be surprised about what security is or isn't

    # being performed.

    cafile = ui.config('hostsecurity', '%s:verifycertsfile' % hostname)

    if s['certfingerprints'] and cafile:

        ui.warn(_('(hostsecurity.%s:verifycertsfile ignored when host '

                  'fingerprints defined; using host fingerprints for '

                  'verification)\n') % hostname)

    # Try to hook up CA certificate validation unless something above

    # makes it not necessary.

    if s['verifymode'] is None:

        # Look at per-host ca file first.

        if cafile:

            cafile = util.expandpath(cafile)

            if not os.path.exists(cafile):

                raise error.Abort(_('path specified by %s does not exist: %s') %

                                  ('hostsecurity.%s:verifycertsfile' % hostname,

                                   cafile))

            s['cafile'] = cafile

        else:

            # Find global certificates file in config.

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

            if cafile:

                cafile = util.expandpath(cafile)

                if not os.path.exists(cafile):

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

                                      cafile)

            else:

                # No global CA certs. See if we can load defaults.

                cafile = _defaultcacerts()

                if cafile:

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

            s['cafile'] = cafile

        # Require certificate validation if CA certs are being loaded and

        # verification hasn't been disabled above.

        if cafile or (_canloaddefaultcerts and s['allowloaddefaultcerts']):

            s['verifymode'] = ssl.CERT_REQUIRED

        else:

            # At this point we don't have a fingerprint, aren't being

            # explicitly insecure, and can't load CA certs. Connecting

            # at this point is insecure. But we do it for BC reasons.

            # TODO abort here to make secure by default.

            s['verifymode'] = ssl.CERT_NONE

    assert s['verifymode'] is not None

    return s

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')

    settings = _hostsettings(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 = settings['verifymode']

    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 settings['cafile'] is not None:

        sslcontext.load_verify_locations(cafile=settings['cafile'])

        caloaded = True

    elif settings['allowloaddefaultcerts']:

        # This is a no-op on old Python.

        sslcontext.load_default_certs()

        caloaded = True

    else:

        caloaded = False

    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,

        'settings': settings,

        '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):

    """Validate a socket meets security requiremnets.

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

    """

    host = sock._hgstate['hostname']

    ui = sock._hgstate['ui']

    settings = sock._hgstate['settings']

    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 settings['disablecertverification']:

        # We don't print the certificate fingerprint because it shouldn't

        # be necessary: if the user requested certificate verification be

        # disabled, they presumably already saw a message about the inability

        # to verify the certificate and this message would have printed the

        # fingerprint. So printing the fingerprint here adds little to no

        # value.

        ui.warn(_('warning: connection security to %s is disabled per current '

                  'settings; communication is susceptible to eavesdropping '

                  'and tampering\n') % host)

        return

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

    # validate the remote cert.

    peerfingerprints = {

    }

    def fmtfingerprint(s):

        return ':'.join([s[x:x + 2] for x in range(0, len(s), 2)])