Extract some code to separate function

Goals include:
- reducing the number of local variables in the main function (so that we
  don't have to worry about saving/restoring them)
- reducing the number exit points in the main function, making it easier to
  update ssl->state only right before we return

library/ssl_tls.c

@@ -4309,62 +4309,16 @@ write_msg:
     return( ret );
 }
 
-int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl )
+/*
+ * Once the certificate message is read, parse it into a cert chain and
+ * perform basic checks, but leave actual verification to the caller
+ */
+static int ssl_parse_certificate_chain( mbedtls_ssl_context *ssl )
 {
-    int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
+    int ret;
     size_t i, n;
-    const mbedtls_ssl_ciphersuite_t * const ciphersuite_info =
-          ssl->transform_negotiate->ciphersuite_info;
-#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
     uint8_t alert;
 
-    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse certificate" ) );
-
-    if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK ||
-        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_PSK ||
-        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_PSK ||
-        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECJPAKE )
-    {
-        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate" ) );
-        ssl->state++;
-        return( 0 );
-    }
-
-#if defined(MBEDTLS_SSL_SRV_C)
-    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER &&
-        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK )
-    {
-        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate" ) );
-        ssl->state++;
-        return( 0 );
-    }
-
-    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER &&
-        authmode == MBEDTLS_SSL_VERIFY_NONE )
-    {
-        ssl->session_negotiate->verify_result = MBEDTLS_X509_BADCERT_SKIP_VERIFY;
-        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate" ) );
-        ssl->state++;
-        return( 0 );
-    }
-#endif
-
-    if( ( ret = mbedtls_ssl_read_record( ssl ) ) != 0 )
-    {
-        /* mbedtls_ssl_read_record may have sent an alert already. We
-           let it decide whether to alert. */
-        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
-        return( ret );
-    }
-
-    ssl->state++;
-
 #if defined(MBEDTLS_SSL_SRV_C)
 #if defined(MBEDTLS_SSL_PROTO_SSL3)
     /*
@@ -4384,10 +4338,7 @@ int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl )
                one. The client should know what's going on, so we
                don't send an alert. */
             ssl->session_negotiate->verify_result = MBEDTLS_X509_BADCERT_MISSING;
-            if( authmode == MBEDTLS_SSL_VERIFY_OPTIONAL )
+            return( MBEDTLS_ERR_SSL_NO_CLIENT_CERTIFICATE );
-                return( 0 );
-            else
-                return( MBEDTLS_ERR_SSL_NO_CLIENT_CERTIFICATE );
         }
     }
 #endif /* MBEDTLS_SSL_PROTO_SSL3 */
@@ -4408,10 +4359,7 @@ int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl )
                one. The client should know what's going on, so we
                don't send an alert. */
             ssl->session_negotiate->verify_result = MBEDTLS_X509_BADCERT_MISSING;
-            if( authmode == MBEDTLS_SSL_VERIFY_OPTIONAL )
+            return( MBEDTLS_ERR_SSL_NO_CLIENT_CERTIFICATE );
-                return( 0 );
-            else
-                return( MBEDTLS_ERR_SSL_NO_CLIENT_CERTIFICATE );
         }
     }
 #endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \
@@ -4555,6 +4503,75 @@ int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl )
     }
 #endif /* MBEDTLS_SSL_RENEGOTIATION && MBEDTLS_SSL_CLI_C */
 
+    return( 0 );
+}
+
+int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl )
+{
+    int ret;
+    const mbedtls_ssl_ciphersuite_t * const ciphersuite_info =
+          ssl->transform_negotiate->ciphersuite_info;
+#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
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse certificate" ) );
+
+    if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK ||
+        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_PSK ||
+        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_PSK ||
+        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECJPAKE )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate" ) );
+        ssl->state++;
+        return( 0 );
+    }
+
+#if defined(MBEDTLS_SSL_SRV_C)
+    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER &&
+        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate" ) );
+        ssl->state++;
+        return( 0 );
+    }
+
+    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER &&
+        authmode == MBEDTLS_SSL_VERIFY_NONE )
+    {
+        ssl->session_negotiate->verify_result = MBEDTLS_X509_BADCERT_SKIP_VERIFY;
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate" ) );
+        ssl->state++;
+        return( 0 );
+    }
+#endif
+
+    if( ( ret = mbedtls_ssl_read_record( ssl ) ) != 0 )
+    {
+        /* mbedtls_ssl_read_record may have sent an alert already. We
+           let it decide whether to alert. */
+        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
+        return( ret );
+    }
+
+    if( ( ret = ssl_parse_certificate_chain( ssl ) ) != 0 )
+    {
+#if defined(MBEDTLS_SSL_SRV_C)
+        if( ret == MBEDTLS_ERR_SSL_NO_CLIENT_CERTIFICATE &&
+            authmode == MBEDTLS_SSL_VERIFY_OPTIONAL )
+        {
+            ret = 0;
+        }
+#endif
+
+        ssl->state++;
+        return( ret );
+    }
+
     if( authmode != MBEDTLS_SSL_VERIFY_NONE )
     {
         mbedtls_x509_crt *ca_chain;
@@ -4641,6 +4658,8 @@ int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl )
 
         if( ret != 0 )
         {
+            uint8_t alert;
+
             /* The certificate may have been rejected for several reasons.
                Pick one and send the corresponding alert. Which alert to send
                may be a subject of debate in some cases. */
@@ -4683,6 +4702,8 @@ int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl )
 #endif /* MBEDTLS_DEBUG_C */
     }
 
+    ssl->state++;
+
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse certificate" ) );
 
     return( ret );