commit 58ab9ba0bd98b992e51390219c39a3c63bdbe5b1
author Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> Wed Aug 14 09:47:38 2024 +0200
committer Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> Mon Sep 02 12:46:03 2024 +0200
tree 5a1bcde890d7e2f737bbddbe7451f276df1cb02c
parent aefc5938b0b73bd3174e6b32c6ebcb4371b29103

Allow optional authentication of the server in 1.3

This is for compatibility, for people transitioning from 1.2 to 1.3.
See https://github.com/Mbed-TLS/mbedtls/issues/9223 "Mandatory server
authentication" and reports linked from there.

In the future we're likely to make server authentication mandatory in
both 1.2 and 1.3. See https://github.com/Mbed-TLS/mbedtls/issues/7080

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>

library/ssl_tls.c

diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 3bcf4f4..dd793d1 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -1354,29 +1354,6 @@
         return ret;
     }
 
-#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
-    /* RFC 8446 section 4.4.3
-     *
-     * If the verification fails, the receiver MUST terminate the handshake with
-     * a "decrypt_error" alert.
-     *
-     * If the client is configured as TLS 1.3 only with optional verify, return
-     * bad config.
-     *
-     */
-    if (mbedtls_ssl_conf_tls13_is_ephemeral_enabled(
-            (mbedtls_ssl_context *) ssl)                            &&
-        ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT                &&
-        ssl->conf->max_tls_version == MBEDTLS_SSL_VERSION_TLS1_3    &&
-        ssl->conf->min_tls_version == MBEDTLS_SSL_VERSION_TLS1_3    &&
-        ssl->conf->authmode == MBEDTLS_SSL_VERIFY_OPTIONAL) {
-        MBEDTLS_SSL_DEBUG_MSG(
-            1, ("Optional verify auth mode "
-                "is not available for TLS 1.3 client"));
-        return MBEDTLS_ERR_SSL_BAD_CONFIG;
-    }
-#endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
-
     if (ssl->conf->f_rng == NULL) {
         MBEDTLS_SSL_DEBUG_MSG(1, ("no RNG provided"));
         return MBEDTLS_ERR_SSL_NO_RNG;
@@ -8190,6 +8167,7 @@
 {
     int ret = 0;
     int crt_expected;
+    /* Authmode: precedence order is SNI if used else configuration */
 #if defined(MBEDTLS_SSL_SRV_C) && defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
     const int authmode = ssl->handshake->sni_authmode != MBEDTLS_SSL_VERIFY_UNSET
                        ? ssl->handshake->sni_authmode

library/ssl_tls13_generic.c

diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 8f8f8c2..4b027de 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -629,22 +629,17 @@
 static int ssl_tls13_validate_certificate(mbedtls_ssl_context *ssl)
 {
     int ret = 0;
-    int authmode = MBEDTLS_SSL_VERIFY_REQUIRED;
     mbedtls_x509_crt *ca_chain;
     mbedtls_x509_crl *ca_crl;
     uint32_t verify_result = 0;
 
-    /* If SNI was used, overwrite authentication mode
-     * from the configuration. */
-#if defined(MBEDTLS_SSL_SRV_C)
-    if (ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER) {
-#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
-        if (ssl->handshake->sni_authmode != MBEDTLS_SSL_VERIFY_UNSET) {
-            authmode = ssl->handshake->sni_authmode;
-        } else
-#endif
-        authmode = ssl->conf->authmode;
-    }
+    /* Authmode: precedence order is SNI if used else configuration */
+#if defined(MBEDTLS_SSL_SRV_C) && defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
+    const int authmode = ssl->handshake->sni_authmode != MBEDTLS_SSL_VERIFY_UNSET
+                       ? ssl->handshake->sni_authmode
+                       : ssl->conf->authmode;
+#else
+    const int authmode = ssl->conf->authmode;
 #endif
 
     /*