Allow to control the minimum SSL version (#3127)

* Allow to control the minimum SSL version

It's useful for applications that has strict security requirements.

* Add tests for minimum SSL version

The commit updates test_tcp_ssl_connect for both sync and async
connections. Now it sets the minimum SSL version. The test is ran with
both TLSv1.2 and TLSv1.3 (if supported).

A new test case is test_tcp_ssl_version_mismatch. The test added for
both sync and async connections. It uses TLS 1.3 on the client side,
and TLS 1.2 on the server side. It expects a connection error. The
test is skipped if TLS 1.3 is not supported.

* Add example of using a minimum TLS version

CHANGES

@@ -1,3 +1,4 @@
+    * Allow to control the minimum SSL version
     * Add an optional lock_name attribute to LockError.
     * Fix return types for `get`, `set_path` and `strappend` in JSONCommands
     * Connection.register_connect_callback() is made public.

docs/examples/ssl_connection_examples.ipynb

@@ -76,6 +76,42 @@
     "ssl_connection.ping()"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Connecting to a Redis instance via SSL, while specifying a minimum TLS version"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "True"
+      ]
+     },
+     "execution_count": 6,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "import redis\n",
+    "import ssl\n",
+    "\n",
+    "ssl_conn = redis.Redis(\n",
+    "    host=\"localhost\",\n",
+    "    port=6666,\n",
+    "    ssl=True,\n",
+    "    ssl_min_version=ssl.TLSVersion.TLSv1_3,\n",
+    ")\n",
+    "ssl_conn.ping()"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},

redis/asyncio/client.py

@@ -2,6 +2,7 @@
 import copy
 import inspect
 import re
+import ssl
 import warnings
 from typing import (
     TYPE_CHECKING,
@@ -225,6 +226,7 @@ def __init__(
         ssl_ca_certs: Optional[str] = None,
         ssl_ca_data: Optional[str] = None,
         ssl_check_hostname: bool = False,
+        ssl_min_version: Optional[ssl.TLSVersion] = None,
         max_connections: Optional[int] = None,
         single_connection_client: bool = False,
         health_check_interval: int = 0,
@@ -331,6 +333,7 @@ def __init__(
                             "ssl_ca_certs": ssl_ca_certs,
                             "ssl_ca_data": ssl_ca_data,
                             "ssl_check_hostname": ssl_check_hostname,
+                            "ssl_min_version": ssl_min_version,
                         }
                     )
             # This arg only used if no pool is passed in

redis/asyncio/cluster.py

@@ -2,6 +2,7 @@
 import collections
 import random
 import socket
+import ssl
 import warnings
 from typing import (
     Any,
@@ -271,6 +272,7 @@ def __init__(
         ssl_certfile: Optional[str] = None,
         ssl_check_hostname: bool = False,
         ssl_keyfile: Optional[str] = None,
+        ssl_min_version: Optional[ssl.TLSVersion] = None,
         protocol: Optional[int] = 2,
         address_remap: Optional[Callable[[str, int], Tuple[str, int]]] = None,
         cache_enabled: bool = False,
@@ -344,6 +346,7 @@ def __init__(
                     "ssl_certfile": ssl_certfile,
                     "ssl_check_hostname": ssl_check_hostname,
                     "ssl_keyfile": ssl_keyfile,
+                    "ssl_min_version": ssl_min_version,
                 }
             )
 

redis/asyncio/connection.py

@@ -822,6 +822,7 @@ def __init__(
         ssl_ca_certs: Optional[str] = None,
         ssl_ca_data: Optional[str] = None,
         ssl_check_hostname: bool = False,
+        ssl_min_version: Optional[ssl.TLSVersion] = None,
         **kwargs,
     ):
         self.ssl_context: RedisSSLContext = RedisSSLContext(
@@ -831,6 +832,7 @@ def __init__(
             ca_certs=ssl_ca_certs,
             ca_data=ssl_ca_data,
             check_hostname=ssl_check_hostname,
+            min_version=ssl_min_version,
         )
         super().__init__(**kwargs)
 
@@ -863,6 +865,10 @@ def ca_data(self):
     def check_hostname(self):
         return self.ssl_context.check_hostname
 
+    @property
+    def min_version(self):
+        return self.ssl_context.min_version
+
 
 class RedisSSLContext:
     __slots__ = (
@@ -873,6 +879,7 @@ class RedisSSLContext:
         "ca_data",
         "context",
         "check_hostname",
+        "min_version",
     )
 
     def __init__(
@@ -883,6 +890,7 @@ def __init__(
         ca_certs: Optional[str] = None,
         ca_data: Optional[str] = None,
         check_hostname: bool = False,
+        min_version: Optional[ssl.TLSVersion] = None,
     ):
         self.keyfile = keyfile
         self.certfile = certfile
@@ -902,6 +910,7 @@ def __init__(
         self.ca_certs = ca_certs
         self.ca_data = ca_data
         self.check_hostname = check_hostname
+        self.min_version = min_version
         self.context: Optional[ssl.SSLContext] = None
 
     def get(self) -> ssl.SSLContext:
@@ -913,6 +922,8 @@ def get(self) -> ssl.SSLContext:
                 context.load_cert_chain(certfile=self.certfile, keyfile=self.keyfile)
             if self.ca_certs or self.ca_data:
                 context.load_verify_locations(cafile=self.ca_certs, cadata=self.ca_data)
+            if self.min_version is not None:
+                context.minimum_version = self.min_version
             self.context = context
         return self.context
 

redis/client.py

@@ -198,6 +198,7 @@ def __init__(
         ssl_validate_ocsp_stapled=False,
         ssl_ocsp_context=None,
         ssl_ocsp_expected_cert=None,
+        ssl_min_version=None,
         max_connections=None,
         single_connection_client=False,
         health_check_interval=0,
@@ -311,6 +312,7 @@ def __init__(
                             "ssl_validate_ocsp": ssl_validate_ocsp,
                             "ssl_ocsp_context": ssl_ocsp_context,
                             "ssl_ocsp_expected_cert": ssl_ocsp_expected_cert,
+                            "ssl_min_version": ssl_min_version,
                         }
                     )
             connection_pool = ConnectionPool(**kwargs)

redis/connection.py

@@ -769,6 +769,7 @@ def __init__(
         ssl_validate_ocsp_stapled=False,
         ssl_ocsp_context=None,
         ssl_ocsp_expected_cert=None,
+        ssl_min_version=None,
         **kwargs,
     ):
         """Constructor
@@ -787,6 +788,7 @@ def __init__(
             ssl_validate_ocsp_stapled: If set, perform a validation on a stapled ocsp response
             ssl_ocsp_context: A fully initialized OpenSSL.SSL.Context object to be used in verifying the ssl_ocsp_expected_cert
             ssl_ocsp_expected_cert: A PEM armoured string containing the expected certificate to be returned from the ocsp verification service.
+            ssl_min_version: The lowest supported SSL version. It affects the supported SSL versions of the SSLContext. None leaves the default provided by ssl module.
 
         Raises:
             RedisError
@@ -819,6 +821,7 @@ def __init__(
         self.ssl_validate_ocsp_stapled = ssl_validate_ocsp_stapled
         self.ssl_ocsp_context = ssl_ocsp_context
         self.ssl_ocsp_expected_cert = ssl_ocsp_expected_cert
+        self.ssl_min_version = ssl_min_version
         super().__init__(**kwargs)
 
     def _connect(self):
@@ -841,6 +844,8 @@ def _connect(self):
             context.load_verify_locations(
                 cafile=self.ca_certs, capath=self.ca_path, cadata=self.ca_data
             )
+        if self.ssl_min_version is not None:
+            context.minimum_version = self.ssl_min_version
         sslsock = context.wrap_socket(sock, server_hostname=self.host)
         if self.ssl_validate_ocsp is True and CRYPTOGRAPHY_AVAILABLE is False:
             raise RedisError("cryptography is not installed.")

tests/test_asyncio/test_connect.py

@@ -10,6 +10,7 @@
     SSLConnection,
     UnixDomainSocketConnection,
 )
+from redis.exceptions import ConnectionError
 
 from ..ssl_utils import get_ssl_filename
 
@@ -50,7 +51,17 @@ async def test_uds_connect(uds_address):
 
 
 @pytest.mark.ssl
-async def test_tcp_ssl_connect(tcp_address):
+@pytest.mark.parametrize(
+    "ssl_min_version",
+    [
+        ssl.TLSVersion.TLSv1_2,
+        pytest.param(
+            ssl.TLSVersion.TLSv1_3,
+            marks=pytest.mark.skipif(not ssl.HAS_TLSv1_3, reason="requires TLSv1.3"),
+        ),
+    ],
+)
+async def test_tcp_ssl_connect(tcp_address, ssl_min_version):
     host, port = tcp_address
     certfile = get_ssl_filename("server-cert.pem")
     keyfile = get_ssl_filename("server-key.pem")
@@ -60,12 +71,44 @@ async def test_tcp_ssl_connect(tcp_address):
         client_name=_CLIENT_NAME,
         ssl_ca_certs=certfile,
         socket_timeout=10,
+        ssl_min_version=ssl_min_version,
     )
     await _assert_connect(conn, tcp_address, certfile=certfile, keyfile=keyfile)
     await conn.disconnect()
 
 
-async def _assert_connect(conn, server_address, certfile=None, keyfile=None):
+@pytest.mark.ssl
+@pytest.mark.skipif(not ssl.HAS_TLSv1_3, reason="requires TLSv1.3")
+async def test_tcp_ssl_version_mismatch(tcp_address):
+    host, port = tcp_address
+    certfile = get_ssl_filename("server-cert.pem")
+    keyfile = get_ssl_filename("server-key.pem")
+    conn = SSLConnection(
+        host=host,
+        port=port,
+        client_name=_CLIENT_NAME,
+        ssl_ca_certs=certfile,
+        socket_timeout=1,
+        ssl_min_version=ssl.TLSVersion.TLSv1_3,
+    )
+    with pytest.raises(ConnectionError):
+        await _assert_connect(
+            conn,
+            tcp_address,
+            certfile=certfile,
+            keyfile=keyfile,
+            ssl_version=ssl.TLSVersion.TLSv1_2,
+        )
+    await conn.disconnect()
+
+
+async def _assert_connect(
+    conn,
+    server_address,
+    certfile=None,
+    keyfile=None,
+    ssl_version=None,
+):
     stop_event = asyncio.Event()
     finished = asyncio.Event()
 
@@ -82,7 +125,9 @@ async def _handler(reader, writer):
     elif certfile:
         host, port = server_address
         context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
-        context.minimum_version = ssl.TLSVersion.TLSv1_2
+        if ssl_version is not None:
+            context.minimum_version = ssl_version
+            context.maximum_version = ssl_version
         context.load_cert_chain(certfile=certfile, keyfile=keyfile)
         server = await asyncio.start_server(_handler, host=host, port=port, ssl=context)
     else:
@@ -94,6 +139,9 @@ async def _handler(reader, writer):
         try:
             await conn.connect()
             await conn.disconnect()
+        except ConnectionError:
+            finished.set()
+            raise
         finally:
             stop_event.set()
             aserver.close()