Harden tls12_finished_verify_data() by checking master key length.

Require master key length to be greater than zero if we're asked to derive
verify data for a finished or peer finished message.

ok tb@

1 files changed, 4 insertions, 1 deletions

diff --git a/src/lib/libssl/tls12_lib.c b/src/lib/libssl/tls12_lib.c
index e7171ba833..f30f3a7b46 100644
--- a/src/lib/libssl/tls12_lib.c
+++ b/src/lib/libssl/tls12_lib.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: tls12_lib.c,v 1.2 2021/04/30 19:26:45 jsing Exp $ */
+/*      $OpenBSD: tls12_lib.c,v 1.3 2021/05/02 15:57:29 jsing Exp $ */
 /*
  * Copyright (c) 2021 Joel Sing <jsing@openbsd.org>
  *
@@ -27,6 +27,9 @@ tls12_finished_verify_data(SSL *s, const char *finished_label,
 
         *out_len = 0;
 
+        if (s->session->master_key_length <= 0)
+                return 0;
+
         if (verify_data_len < TLS1_FINISH_MAC_LENGTH)
                 return 0;