Merge pull request #1865 from docker/dperny-change-tls-default

Change default TLS version

docker/tls.py

@@ -37,13 +37,33 @@ class TLSConfig(object):
         self.assert_hostname = assert_hostname
         self.assert_fingerprint = assert_fingerprint
 
-        # TLS v1.0 seems to be the safest default; SSLv23 fails in mysterious
-        # ways: https://github.com/docker/docker-py/issues/963
-
-        self.ssl_version = ssl_version or ssl.PROTOCOL_TLSv1
-
-        # "tls" and "tls_verify" must have both or neither cert/key files
-        # In either case, Alert the user when both are expected, but any are
+        # TODO(dperny): according to the python docs, PROTOCOL_TLSvWhatever is
+        # depcreated, and it's recommended to use OPT_NO_TLSvWhatever instead
+        # to exclude versions. But I think that might require a bigger
+        # architectural change, so I've opted not to pursue it at this time
+
+        # If the user provides an SSL version, we should use their preference
+        if ssl_version:
+            self.ssl_version = ssl_version
+        else:
+            # If the user provides no ssl version, we should default to
+            # TLSv1_2.  This option is the most secure, and will work for the
+            # majority of users with reasonably up-to-date software. However,
+            # before doing so, detect openssl version to ensure we can support
+            # it.
+            if ssl.OPENSSL_VERSION_INFO[:3] >= (1, 0, 1) and hasattr(
+                    ssl, 'PROTOCOL_TLSv1_2'):
+                # If the OpenSSL version is high enough to support TLSv1_2,
+                # then we should use it.
+                self.ssl_version = getattr(ssl, 'PROTOCOL_TLSv1_2')
+            else:
+                # Otherwise, TLS v1.0 seems to be the safest default;
+                # SSLv23 fails in mysterious ways:
+                # https://github.com/docker/docker-py/issues/963
+                self.ssl_version = ssl.PROTOCOL_TLSv1
+
+        # "tls" and "tls_verify" must have both or neither cert/key files In
+        # either case, Alert the user when both are expected, but any are
         # missing.
 
         if client_cert: