fix various issues

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index 88f0fe5..6b8f8e1 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -655,6 +655,8 @@
     size_t transcript_len;
 
     unsigned char *base_key = NULL;
+    mbedtls_ssl_tls13_handshake_secrets *tls13_hs_secrets =
+                                            &ssl->handshake->tls13_hs_secrets;
 
     mbedtls_md_type_t const md_type = ssl->handshake->ciphersuite_info->mac;
     const mbedtls_md_info_t* const md_info =
@@ -664,7 +666,10 @@
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> mbedtls_ssl_tls13_calculate_verify_data" ) );
 
     if( dst_len < md_size )
-        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+    {
+        ret = MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL;
+        goto exit;
+    }
 
     ret = mbedtls_ssl_get_handshake_transcript( ssl, md_type,
                                                 transcript, sizeof( transcript ),
@@ -677,9 +682,9 @@
     MBEDTLS_SSL_DEBUG_BUF( 4, "handshake hash", transcript, transcript_len );
 
     if( from == MBEDTLS_SSL_IS_CLIENT )
-        base_key = ssl->handshake->tls13_hs_secrets.client_handshake_traffic_secret;
+        base_key = tls13_hs_secrets->client_handshake_traffic_secret;
     else
-        base_key = ssl->handshake->tls13_hs_secrets.server_handshake_traffic_secret;
+        base_key = tls13_hs_secrets->server_handshake_traffic_secret;
 
     ret = ssl_tls13_calc_finished_core( md_type, base_key, transcript, dst );
     if( ret != 0 )
@@ -692,9 +697,15 @@
 exit:
     /* Erase handshake secrets */
     if( from == MBEDTLS_SSL_IS_CLIENT )
-        mbedtls_platform_zeroize( base_key, sizeof( ssl->handshake->tls13_hs_secrets.client_handshake_traffic_secret ) );
+    {
+        mbedtls_platform_zeroize( base_key,
+                sizeof( tls13_hs_secrets->client_handshake_traffic_secret ) );
+    }
     else
-        mbedtls_platform_zeroize( base_key, sizeof( ssl->handshake->tls13_hs_secrets.server_handshake_traffic_secret ) );
+    {
+        mbedtls_platform_zeroize( base_key,
+                sizeof( tls13_hs_secrets->server_handshake_traffic_secret ) );
+    }
     mbedtls_platform_zeroize( transcript, sizeof( transcript ) );
     return( ret );
 }