TLS: Session caching configuration support. (#7420)

* TLS: Session caching configuration support.
* TLS: Remove redundant config initialization.

TLS.md

@@ -68,8 +68,6 @@ but there are probably other good reasons to improve that part anyway.
 To-Do List
 ----------
 
-- [ ] Add session caching support. Check if/how it's handled by clients to
-  assess how useful/important it is.
 - [ ] redis-benchmark support. The current implementation is a mix of using
   hiredis for parsing and basic networking (establishing connections), but
   directly manipulating sockets for most actions. This will need to be cleaned

redis.conf

@@ -199,6 +199,22 @@ tcp-keepalive 300
 #
 # tls-prefer-server-ciphers yes
 
+# By default, TLS session caching is enabled to allow faster and less expensive
+# reconnections by clients that support it. Use the following directive to disable
+# caching.
+#
+# tls-session-caching no
+
+# Change the default number of TLS sessions cached. A zero value sets the cache
+# to unlimited size. The default size is 20480.
+#
+# tls-session-cache-size 5000
+
+# Change the default timeout of cached TLS sessions. The default timeout is 300
+# seconds.
+#
+# tls-session-cache-timeout 60
+
 ################################# GENERAL #####################################
 
 # By default Redis does not run as a daemon. Use 'yes' if you need it.

src/config.c

@@ -2071,7 +2071,7 @@ static int updateTlsCfg(char *val, char *prev, char **err) {
     UNUSED(prev);
     UNUSED(err);
     if (tlsConfigure(&server.tls_ctx_config) == C_ERR) {
-        *err = "Unable to configure tls-cert-file. Check server logs.";
+        *err = "Unable to update TLS configuration. Check server logs.";
         return 0;
     }
     return 1;
@@ -2081,6 +2081,12 @@ static int updateTlsCfgBool(int val, int prev, char **err) {
     UNUSED(prev);
     return updateTlsCfg(NULL, NULL, err);
 }
+
+static int updateTlsCfgInt(long long val, long long prev, char **err) {
+    UNUSED(val);
+    UNUSED(prev);
+    return updateTlsCfg(NULL, NULL, err);
+}
 #endif  /* USE_OPENSSL */
 
 standardConfig configs[] = {
@@ -2216,10 +2222,13 @@ standardConfig configs[] = {
 
 #ifdef USE_OPENSSL
     createIntConfig("tls-port", NULL, IMMUTABLE_CONFIG, 0, 65535, server.tls_port, 0, INTEGER_CONFIG, NULL, NULL), /* TCP port. */
+    createIntConfig("tls-session-cache-size", NULL, MODIFIABLE_CONFIG, 0, INT_MAX, server.tls_ctx_config.session_cache_size, 20*1024, INTEGER_CONFIG, NULL, updateTlsCfgInt),
+    createIntConfig("tls-session-cache-timeout", NULL, MODIFIABLE_CONFIG, 0, INT_MAX, server.tls_ctx_config.session_cache_timeout, 300, INTEGER_CONFIG, NULL, updateTlsCfgInt),
     createBoolConfig("tls-cluster", NULL, MODIFIABLE_CONFIG, server.tls_cluster, 0, NULL, NULL),
     createBoolConfig("tls-replication", NULL, MODIFIABLE_CONFIG, server.tls_replication, 0, NULL, NULL),
     createBoolConfig("tls-auth-clients", NULL, MODIFIABLE_CONFIG, server.tls_auth_clients, 1, NULL, NULL),
     createBoolConfig("tls-prefer-server-ciphers", NULL, MODIFIABLE_CONFIG, server.tls_ctx_config.prefer_server_ciphers, 0, NULL, updateTlsCfgBool),
+    createBoolConfig("tls-session-caching", NULL, MODIFIABLE_CONFIG, server.tls_ctx_config.session_caching, 1, NULL, updateTlsCfgBool),
     createStringConfig("tls-cert-file", NULL, MODIFIABLE_CONFIG, EMPTY_STRING_IS_NULL, server.tls_ctx_config.cert_file, NULL, NULL, updateTlsCfg),
     createStringConfig("tls-key-file", NULL, MODIFIABLE_CONFIG, EMPTY_STRING_IS_NULL, server.tls_ctx_config.key_file, NULL, NULL, updateTlsCfg),
     createStringConfig("tls-dh-params-file", NULL, MODIFIABLE_CONFIG, EMPTY_STRING_IS_NULL, server.tls_ctx_config.dh_params_file, NULL, NULL, updateTlsCfg),

src/server.h

@@ -1011,6 +1011,9 @@ typedef struct redisTLSContextConfig {
     char *ciphers;
     char *ciphersuites;
     int prefer_server_ciphers;
+    int session_caching;
+    int session_cache_size;
+    int session_cache_timeout;
 } redisTLSContextConfig;
 
 /*-----------------------------------------------------------------------------

src/tls.c

@@ -148,9 +148,6 @@ void tlsInit(void) {
     }
 
     pending_list = listCreate();
-
-    /* Server configuration */
-    server.tls_auth_clients = 1;    /* Secure by default */
 }
 
 /* Attempt to configure/reconfigure TLS. This operation is atomic and will
@@ -184,6 +181,15 @@ int tlsConfigure(redisTLSContextConfig *ctx_config) {
     SSL_CTX_set_options(ctx, SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS);
 #endif
 
+    if (ctx_config->session_caching) {
+        SSL_CTX_set_session_cache_mode(ctx, SSL_SESS_CACHE_SERVER);
+        SSL_CTX_sess_set_cache_size(ctx, ctx_config->session_cache_size);
+        SSL_CTX_set_timeout(ctx, ctx_config->session_cache_timeout);
+        SSL_CTX_set_session_id_context(ctx, (void *) "redis", 5);
+    } else {
+        SSL_CTX_set_session_cache_mode(ctx, SSL_SESS_CACHE_OFF);
+    }
+
     int protocols = parseProtocolsConfig(ctx_config->protocols);
     if (protocols == -1) goto error;
 

tests/unit/introspection.tcl

@@ -78,17 +78,8 @@ start_server {tags {"introspection"}} {
             syslog-facility
             databases
             port
-            io-threads
             tls-port
-            tls-prefer-server-ciphers
-            tls-cert-file
-            tls-key-file
-            tls-dh-params-file
-            tls-ca-cert-file
-            tls-ca-cert-dir
-            tls-protocols
-            tls-ciphers
-            tls-ciphersuites
+            io-threads
             logfile
             unixsocketperm
             slaveof
@@ -100,6 +91,23 @@ start_server {tags {"introspection"}} {
             bgsave_cpulist
         }
 
+        if {!$::tls} {
+            append skip_configs {
+                tls-prefer-server-ciphers
+                tls-session-cache-timeout
+                tls-session-cache-size
+                tls-session-caching
+                tls-cert-file
+                tls-key-file
+                tls-dh-params-file
+                tls-ca-cert-file
+                tls-ca-cert-dir
+                tls-protocols
+                tls-ciphers
+                tls-ciphersuites
+            }
+        }
+
         set configs {}
         foreach {k v} [r config get *] {
             if {[lsearch $skip_configs $k] != -1} {