From e273f7203dfa7d6533ed868a02a4a8ae73138a66 Mon Sep 17 00:00:00 2001
From: Ronald Cron <ronald.cron@arm.com>
Date: Tue, 13 Feb 2024 18:22:26 +0100
Subject: [PATCH] tls13: client: Improve CCS handling

Call unconditionally the CCS writing function
when sending a CCS may be necessary in the
course of an handshake. Enforce in the writing
function and only in the writing function that
only one CCS is sent.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
---
 library/ssl_tls13_client.c  | 18 ++++++------------
 library/ssl_tls13_generic.c |  6 ++++++
 library/ssl_tls13_server.c  |  9 +++------
 3 files changed, 15 insertions(+), 18 deletions(-)

diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index 5d7a495901..cedebad29a 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -3063,23 +3063,17 @@ int mbedtls_ssl_tls13_handshake_client_step(mbedtls_ssl_context *ssl)
              */
 #if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
         case MBEDTLS_SSL_CLIENT_CCS_BEFORE_2ND_CLIENT_HELLO:
-            ret = 0;
-            if (ssl->handshake->ccs_count == 0) {
-                ret = mbedtls_ssl_tls13_write_change_cipher_spec(ssl);
-                if (ret != 0) {
-                    break;
-                }
+            ret = mbedtls_ssl_tls13_write_change_cipher_spec(ssl);
+            if (ret != 0) {
+                break;
             }
             mbedtls_ssl_handshake_set_state(ssl, MBEDTLS_SSL_CLIENT_HELLO);
             break;
 
         case MBEDTLS_SSL_CLIENT_CCS_AFTER_SERVER_FINISHED:
-            ret = 0;
-            if (ssl->handshake->ccs_count == 0) {
-                ret = mbedtls_ssl_tls13_write_change_cipher_spec(ssl);
-                if (ret != 0) {
-                    break;
-                }
+            ret = mbedtls_ssl_tls13_write_change_cipher_spec(ssl);
+            if (ret != 0) {
+                break;
             }
             mbedtls_ssl_handshake_set_state(ssl, MBEDTLS_SSL_CLIENT_CERTIFICATE);
             break;
diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 386a754024..c6bb770278 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -1379,6 +1379,12 @@ int mbedtls_ssl_tls13_write_change_cipher_spec(mbedtls_ssl_context *ssl)
 
     MBEDTLS_SSL_DEBUG_MSG(2, ("=> write change cipher spec"));
 
+    /* Only one CCS to send. */
+    if (ssl->handshake->ccs_count > 0) {
+        ret = 0;
+        goto cleanup;
+    }
+
     /* Write CCS message */
     MBEDTLS_SSL_PROC_CHK(ssl_tls13_write_change_cipher_spec_body(
                              ssl, ssl->out_msg,
diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index 05693f3bfc..f9f3cc5714 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -3482,12 +3482,9 @@ int mbedtls_ssl_tls13_handshake_server_step(mbedtls_ssl_context *ssl)
             break;
 
         case MBEDTLS_SSL_SERVER_CCS_AFTER_SERVER_HELLO:
-            ret = 0;
-            if (ssl->handshake->ccs_count == 0) {
-                ret = mbedtls_ssl_tls13_write_change_cipher_spec(ssl);
-                if (ret != 0) {
-                    break;
-                }
+            ret = mbedtls_ssl_tls13_write_change_cipher_spec(ssl);
+            if (ret != 0) {
+                break;
             }
             mbedtls_ssl_handshake_set_state(ssl, MBEDTLS_SSL_ENCRYPTED_EXTENSIONS);
             break;