Add match_hostname implementation and monkey-patch for py<3.5

Signed-off-by: Joffrey F <joffrey@docker.com>

docker/ssladapter/ssl_match_hostname.py

+# Slightly modified version of match_hostname in python's ssl library
+# https://hg.python.org/cpython/file/tip/Lib/ssl.py
+# Changed to make code python 2.x compatible (unicode strings for ip_address
+# and 3.5-specific var assignment syntax)
+
+import ipaddress
+import re
+
+try:
+    from ssl import CertificateError
+except ImportError:
+    CertificateError = ValueError
+
+import six
+
+
+def _ipaddress_match(ipname, host_ip):
+    """Exact matching of IP addresses.
+
+    RFC 6125 explicitly doesn't define an algorithm for this
+    (section 1.7.2 - "Out of Scope").
+    """
+    # OpenSSL may add a trailing newline to a subjectAltName's IP address
+    ip = ipaddress.ip_address(six.text_type(ipname.rstrip()))
+    return ip == host_ip
+
+
+def _dnsname_match(dn, hostname, max_wildcards=1):
+    """Matching according to RFC 6125, section 6.4.3
+
+    http://tools.ietf.org/html/rfc6125#section-6.4.3
+    """
+    pats = []
+    if not dn:
+        return False
+
+    split_dn = dn.split(r'.')
+    leftmost, remainder = split_dn[0], split_dn[1:]
+
+    wildcards = leftmost.count('*')
+    if wildcards > max_wildcards:
+        # Issue #17980: avoid denials of service by refusing more
+        # than one wildcard per fragment.  A survey of established
+        # policy among SSL implementations showed it to be a
+        # reasonable choice.
+        raise CertificateError(
+            "too many wildcards in certificate DNS name: " + repr(dn))
+
+    # speed up common case w/o wildcards
+    if not wildcards:
+        return dn.lower() == hostname.lower()
+
+    # RFC 6125, section 6.4.3, subitem 1.
+    # The client SHOULD NOT attempt to match a presented identifier in which
+    # the wildcard character comprises a label other than the left-most label.
+    if leftmost == '*':
+        # When '*' is a fragment by itself, it matches a non-empty dotless
+        # fragment.
+        pats.append('[^.]+')
+    elif leftmost.startswith('xn--') or hostname.startswith('xn--'):
+        # RFC 6125, section 6.4.3, subitem 3.
+        # The client SHOULD NOT attempt to match a presented identifier
+        # where the wildcard character is embedded within an A-label or
+        # U-label of an internationalized domain name.
+        pats.append(re.escape(leftmost))
+    else:
+        # Otherwise, '*' matches any dotless string, e.g. www*
+        pats.append(re.escape(leftmost).replace(r'\*', '[^.]*'))
+
+    # add the remaining fragments, ignore any wildcards
+    for frag in remainder:
+        pats.append(re.escape(frag))
+
+    pat = re.compile(r'\A' + r'\.'.join(pats) + r'\Z', re.IGNORECASE)
+    return pat.match(hostname)
+
+
+def match_hostname(cert, hostname):
+    """Verify that *cert* (in decoded format as returned by
+    SSLSocket.getpeercert()) matches the *hostname*.  RFC 2818 and RFC 6125
+    rules are followed, but IP addresses are not accepted for *hostname*.
+
+    CertificateError is raised on failure. On success, the function
+    returns nothing.
+    """
+    if not cert:
+        raise ValueError("empty or no certificate, match_hostname needs a "
+                         "SSL socket or SSL context with either "
+                         "CERT_OPTIONAL or CERT_REQUIRED")
+    try:
+        host_ip = ipaddress.ip_address(six.text_type(hostname))
+    except ValueError:
+        # Not an IP address (common case)
+        host_ip = None
+    dnsnames = []
+    san = cert.get('subjectAltName', ())
+    for key, value in san:
+        if key == 'DNS':
+            if host_ip is None and _dnsname_match(value, hostname):
+                return
+            dnsnames.append(value)
+        elif key == 'IP Address':
+            if host_ip is not None and _ipaddress_match(value, host_ip):
+                return
+            dnsnames.append(value)
+    if not dnsnames:
+        # The subject is only checked when there is no dNSName entry
+        # in subjectAltName
+        for sub in cert.get('subject', ()):
+            for key, value in sub:
+                # XXX according to RFC 2818, the most specific Common Name
+                # must be used.
+                if key == 'commonName':
+                    if _dnsname_match(value, hostname):
+                        return
+                    dnsnames.append(value)
+    if len(dnsnames) > 1:
+        raise CertificateError(
+            "hostname %r doesn't match either of %s"
+            % (hostname, ', '.join(map(repr, dnsnames))))
+    elif len(dnsnames) == 1:
+        raise CertificateError(
+            "hostname %r doesn't match %r"
+            % (hostname, dnsnames[0])
+        )
+    else:
+        raise CertificateError(
+            "no appropriate commonName or "
+            "subjectAltName fields were found"
+        )

docker/ssladapter/ssladapter.py

@@ -2,6 +2,8 @@
       https://lukasa.co.uk/2013/01/Choosing_SSL_Version_In_Requests/
       https://github.com/kennethreitz/requests/pull/799
 """
+import sys
+
 from distutils.version import StrictVersion
 from requests.adapters import HTTPAdapter
 
@@ -10,8 +12,15 @@ try:
 except ImportError:
     import urllib3
 
+
 PoolManager = urllib3.poolmanager.PoolManager
 
+# Monkey-patching match_hostname with a version that supports
+# IP-address checking. Not necessary for Python 3.5 and above
+if sys.version_info[0] < 3 or sys.version_info[1] < 5:
+    from .ssl_match_hostname import match_hostname
+    urllib3.connection.match_hostname = match_hostname
+
 
 class SSLAdapter(HTTPAdapter):
     '''An HTTPS Transport Adapter that uses an arbitrary SSL version.'''