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@

diff --git a/lib/libssl/tls12_lib.c b/lib/libssl/tls12_lib.c
index e7171ba..f30f3a7 100644 (file)
--- a/lib/libssl/tls12_lib.c
+++ b/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;