From a5ce0fd77f51651f8bd1a7fe4c423ee7f87edaa3 Mon Sep 17 00:00:00 2001
From: Hanno Becker <hanno.becker@arm.com>
Date: Tue, 23 Oct 2018 11:54:44 +0100
Subject: [PATCH] Don't suggest the use of a PSK suite if no PSK configured on
 client

---
 library/ssl_cli.c | 38 +++++++++++++++++++++++++++++++++++---
 1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index ff576f3a8..70ce90f75 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -51,6 +51,27 @@
 #include "mbedtls/platform_util.h"
 #endif
 
+#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+static int ssl_conf_has_psk( mbedtls_ssl_config const *conf )
+{
+    if( conf->psk_identity     == NULL ||
+        conf->psk_identity_len == 0     )
+    {
+        return( 0 );
+    }
+
+    if( conf->psk != NULL && conf->psk_len != 0 )
+        return( 1 );
+
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+    if( conf->psk_opaque != 0 )
+        return( 1 );
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
+
+    return( 0 );
+}
+#endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
+
 #if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
 static void ssl_write_hostname_ext( mbedtls_ssl_context *ssl,
                                     unsigned char *buf,
@@ -754,6 +775,15 @@ static int ssl_validate_ciphersuite( const mbedtls_ssl_ciphersuite_t * suite_inf
         return( 1 );
 #endif
 
+    /* Don't suggest PSK-based ciphersuite if no PSK is available. */
+#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+    if( mbedtls_ssl_ciphersuite_uses_psk( suite_info ) &&
+        ssl_conf_has_psk( ssl ) == 0 )
+    {
+        return( 1 );
+    }
+#endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
+
     return( 0 );
 }
 
@@ -3007,10 +3037,12 @@ ecdh_calc_secret:
         /*
          * opaque psk_identity<0..2^16-1>;
          */
-        if( ssl->conf->psk == NULL || ssl->conf->psk_identity == NULL )
+        if( ssl_conf_has_psk( ssl ) == 0 )
         {
-            MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no private key for PSK" ) );
-            return( MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED );
+            /* We don't offer PSK suites if we don't have a PSK,
+             * and we check that the server's choice is among the
+             * ciphersuites we offered, so this should never happen. */
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
         }
 
         i = 4;