Add redis SSL configuration options (#15312)

* Add SSL options to redis config

* fix lint issues

* Add documentation and changelog file

* add missing . at the end of the changelog

* Move client context factory to new file

* Rename ssl to tls and fix typo

* fix lint issues

* Added when redis attributes were added

7 files changed, 98 insertions, 14 deletions

diff --git a/changelog.d/15312.feature b/changelog.d/15312.feature
new file mode 100644
index 0000000000..e4e972cfeb
--- /dev/null
+++ b/changelog.d/15312.feature
@@ -0,0 +1 @@
+Add redis TLS configuration options.
\ No newline at end of file
diff --git a/contrib/docker_compose_workers/README.md b/contrib/docker_compose_workers/README.md
index d3cdfe5614..ebb225fba6 100644
--- a/contrib/docker_compose_workers/README.md
+++ b/contrib/docker_compose_workers/README.md
@@ -70,6 +70,10 @@ redis:
   port: 6379
   # dbid:  <redis_logical_db_id>
   # password: <secret_password>  
+  # use_tls: True
+  # certificate_file: <path_to_certificate>
+  # private_key_file: <path_to_private_key>
+  # ca_file: <path_to_ca_certificate>
 ```
 
 This assumes that your Redis service is called `redis` in your Docker Compose file.
diff --git a/docs/usage/configuration/config_documentation.md b/docs/usage/configuration/config_documentation.md
index dc965b4119..93b132b6e4 100644
--- a/docs/usage/configuration/config_documentation.md
+++ b/docs/usage/configuration/config_documentation.md
@@ -3981,9 +3981,16 @@ This setting has the following sub-options:
    localhost and 6379
 * `password`: Optional password if configured on the Redis instance.
 * `dbid`: Optional redis dbid if needs to connect to specific redis logical db.
+* `use_tls`: Whether to use tls connection. Defaults to false.
+* `certificate_file`: Optional path to the certificate file
+* `private_key_file`: Optional path to the private key file
+* `ca_file`: Optional path to the CA certificate file. Use this one or:
+* `ca_path`: Optional path to the folder containing the CA certificate file
 
   _Added in Synapse 1.78.0._
 
+  _Changed in Synapse 1.84.0: Added use\_tls, certificate\_file, private\_key\_file, ca\_file and ca\_path attributes_
+
 Example configuration:
 ```yaml
 redis:
@@ -3992,6 +3999,10 @@ redis:
   port: 6379
   password: <secret_password>
   dbid: <dbid>
+  #use_tls: True
+  #certificate_file: <path_to_the_certificate_file>
+  #private_key_file: <path_to_the_private_key_file>
+  #ca_file: <path_to_the_ca_certificate_file>
 ```
 ---
 ## Individual worker configuration
diff --git a/synapse/config/redis.py b/synapse/config/redis.py
index e6a75be434..636cb450b8 100644
--- a/synapse/config/redis.py
+++ b/synapse/config/redis.py
@@ -35,3 +35,9 @@ class RedisConfig(Config):
         self.redis_port = redis_config.get("port", 6379)
         self.redis_dbid = redis_config.get("dbid", None)
         self.redis_password = redis_config.get("password")
+
+        self.redis_use_tls = redis_config.get("use_tls", False)
+        self.redis_certificate = redis_config.get("certificate_file", None)
+        self.redis_private_key = redis_config.get("private_key_file", None)
+        self.redis_ca_file = redis_config.get("ca_file", None)
+        self.redis_ca_path = redis_config.get("ca_path", None)
diff --git a/synapse/replication/tcp/context.py b/synapse/replication/tcp/context.py
new file mode 100644
index 0000000000..4688b2200b
--- /dev/null
+++ b/synapse/replication/tcp/context.py
@@ -0,0 +1,34 @@
+# Copyright 2023 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from OpenSSL.SSL import Context
+from twisted.internet import ssl
+
+from synapse.config.redis import RedisConfig
+
+
+class ClientContextFactory(ssl.ClientContextFactory):
+    def __init__(self, redis_config: RedisConfig):
+        self.redis_config = redis_config
+
+    def getContext(self) -> Context:
+        ctx = super().getContext()
+        if self.redis_config.redis_certificate:
+            ctx.use_certificate_file(self.redis_config.redis_certificate)
+        if self.redis_config.redis_private_key:
+            ctx.use_privatekey_file(self.redis_config.redis_private_key)
+        if self.redis_config.redis_ca_file:
+            ctx.load_verify_locations(cafile=self.redis_config.redis_ca_file)
+        elif self.redis_config.redis_ca_path:
+            ctx.load_verify_locations(capath=self.redis_config.redis_ca_path)
+        return ctx
diff --git a/synapse/replication/tcp/handler.py b/synapse/replication/tcp/handler.py
index 2290b3e6fe..233ad61d49 100644
--- a/synapse/replication/tcp/handler.py
+++ b/synapse/replication/tcp/handler.py
@@ -46,6 +46,7 @@ from synapse.replication.tcp.commands import (
     UserIpCommand,
     UserSyncCommand,
 )
+from synapse.replication.tcp.context import ClientContextFactory
 from synapse.replication.tcp.protocol import IReplicationConnection
 from synapse.replication.tcp.streams import (
     STREAMS_MAP,
@@ -348,13 +349,27 @@ class ReplicationCommandHandler:
             outbound_redis_connection,
             channel_names=self._channels_to_subscribe_to,
         )
-        hs.get_reactor().connectTCP(
-            hs.config.redis.redis_host,
-            hs.config.redis.redis_port,
-            self._factory,
-            timeout=30,
-            bindAddress=None,
-        )
+
+        reactor = hs.get_reactor()
+        redis_config = hs.config.redis
+        if hs.config.redis.redis_use_tls:
+            ssl_context_factory = ClientContextFactory(hs.config.redis)
+            reactor.connectSSL(
+                redis_config.redis_host,
+                redis_config.redis_port,
+                self._factory,
+                ssl_context_factory,
+                timeout=30,
+                bindAddress=None,
+            )
+        else:
+            reactor.connectTCP(
+                redis_config.redis_host,
+                redis_config.redis_port,
+                self._factory,
+                timeout=30,
+                bindAddress=None,
+            )
 
     def get_streams(self) -> Dict[str, Stream]:
         """Get a map from stream name to all streams."""
diff --git a/synapse/replication/tcp/redis.py b/synapse/replication/tcp/redis.py
index dfc061eb5e..c8f4bf8b27 100644
--- a/synapse/replication/tcp/redis.py
+++ b/synapse/replication/tcp/redis.py
@@ -35,6 +35,7 @@ from synapse.replication.tcp.commands import (
     ReplicateCommand,
     parse_command_from_line,
 )
+from synapse.replication.tcp.context import ClientContextFactory
 from synapse.replication.tcp.protocol import (
     IReplicationConnection,
     tcp_inbound_commands_counter,
@@ -386,12 +387,24 @@ def lazyConnection(
     factory.continueTrying = reconnect
 
     reactor = hs.get_reactor()
-    reactor.connectTCP(
-        host,
-        port,
-        factory,
-        timeout=30,
-        bindAddress=None,
-    )
+
+    if hs.config.redis.redis_use_tls:
+        ssl_context_factory = ClientContextFactory(hs.config.redis)
+        reactor.connectSSL(
+            host,
+            port,
+            factory,
+            ssl_context_factory,
+            timeout=30,
+            bindAddress=None,
+        )
+    else:
+        reactor.connectTCP(
+            host,
+            port,
+            factory,
+            timeout=30,
+            bindAddress=None,
+        )
 
     return factory.handler