Mercurial > hg
view mercurial/sslutil.py @ 28850:3819c349b194
sslutil: document and slightly refactor validation logic
This main purpose of this patch is to make it clearer that fingerprint
pinning takes precedence over CA verification. This will make
subsequent refactoring to the validation code easier to read.
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Sun, 10 Apr 2016 11:02:58 -0700 |
parents | 1fde84d42f9c |
children | 693b856a4d45 |
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# 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 wrapsocket(sock, keyfile, certfile, ui, cert_reqs=ssl.CERT_NONE, ca_certs=None, 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 required') # 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) else: # This is a no-op on old Python. 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 error.Abort(_('ssl connection failed')) 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 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 = {'ui': ui} 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 error.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': ssl.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 if not sock.cipher(): # work around http://bugs.python.org/issue13721 raise error.Abort(_('%s ssl connection error') % host) 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 = self.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')) self.ui.debug('%s certificate matched fingerprint %s\n' % (host, nicefingerprint)) return # No pinned fingerprint. Establish trust by looking at the CAs. cacerts = self.ui.config('web', 'cacerts') if cacerts != '!': 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) self.ui.debug('%s certificate successfully verified\n' % host) elif strict: raise error.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))