Mercurial > hg
view mercurial/sslutil.py @ 29446:2f7f1e10f840
sslutil: display a better error message when CA file loading fails
Before, sslcontext.load_verify_locations() would raise a
ssl.SSLError which would be caught further up the stack and converted
to a urlerror. By that time, we lost track of what actually errored.
Trapping the error here gives users a slightly more actionable error
message.
The behavior between Python <2.7.9 and Python 2.7.9+ differs. This
is because our fake SSLContext class installed on <2.7.9 doesn't
actually do anything during load_verify_locations: it defers actions
until wrap_socket() time. Unfortunately, a number of errors can occur
at wrap_socket() time and we're unable to ascertain what the root
cause is. But that shouldn't stop us from providing better error
messages to people running a modern and secure Python version.
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Wed, 29 Jun 2016 19:37:38 -0700 |
parents | e1778b9c8d53 |
children | 13edc11eb7b7 |
line wrap: on
line source
# 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 hashlib 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 # is insecure. We allow the connection and abort during # validation (once we have the fingerprint to print to the # user). 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: try: sslcontext.load_verify_locations(cafile=settings['cafile']) except ssl.SSLError as e: raise error.Abort(_('error loading CA file %s: %s') % ( settings['cafile'], e.args[1]), hint=_('file is empty or malformed?')) 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') 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 = { 'sha1': hashlib.sha1(peercert).hexdigest(), 'sha256': hashlib.sha256(peercert).hexdigest(), 'sha512': hashlib.sha512(peercert).hexdigest(), } def fmtfingerprint(s): return ':'.join([s[x:x + 2] for x in range(0, len(s), 2)]) nicefingerprint = 'sha256:%s' % fmtfingerprint(peerfingerprints['sha256']) if settings['certfingerprints']: for hash, fingerprint in settings['certfingerprints']: if peerfingerprints[hash].lower() == fingerprint: ui.debug('%s certificate matched fingerprint %s:%s\n' % (host, hash, fmtfingerprint(fingerprint))) return # Pinned fingerprint didn't match. This is a fatal error. if settings['legacyfingerprint']: section = 'hostfingerprint' nice = fmtfingerprint(peerfingerprints['sha1']) else: section = 'hostsecurity' nice = '%s:%s' % (hash, fmtfingerprint(peerfingerprints[hash])) raise error.Abort(_('certificate for %s has unexpected ' 'fingerprint %s') % (host, nice), hint=_('check %s configuration') % section) # Security is enabled but no CAs are loaded. We can't establish trust # for the cert so abort. if not sock._hgstate['caloaded']: raise error.Abort( _('unable to verify security of %s (no loaded CA certificates); ' 'refusing to connect') % host, hint=_('see https://mercurial-scm.org/wiki/SecureConnections for ' 'how to configure Mercurial to avoid this error or set ' 'hostsecurity.%s:fingerprints=%s to trust this server') % (host, nicefingerprint)) msg = _verifycert(peercert2, host) if msg: raise error.Abort(_('%s certificate error: %s') % (host, msg), hint=_('set hostsecurity.%s:certfingerprints=%s ' 'config setting or use --insecure to connect ' 'insecurely') % (host, nicefingerprint))