Switch back to the legacy stack where the maximum is less than TLSv1.3.

This allows a server configured to only support TLSv1.2 and earlier, to
correctly handle connections from a TLSv1.3 capable client.

Issue reported by pvk@

ok inoguchi@ tb@

1 files changed, 2 insertions, 2 deletions

diff --git a/src/lib/libssl/tls13_server.c b/src/lib/libssl/tls13_server.c
index ec612df90e..cd5f19afeb 100644
--- a/src/lib/libssl/tls13_server.c
+++ b/src/lib/libssl/tls13_server.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tls13_server.c,v 1.45 2020/05/11 17:49:46 jsing Exp $ */
+/* $OpenBSD: tls13_server.c,v 1.46 2020/05/13 17:53:15 jsing Exp $ */
 /*
  * Copyright (c) 2019, 2020 Joel Sing <jsing@openbsd.org>
  * Copyright (c) 2020 Bob Beck <beck@openbsd.org>
@@ -115,7 +115,7 @@ tls13_client_hello_process(struct tls13_ctx *ctx, CBS *cbs)
         if (!CBS_get_u8_length_prefixed(cbs, &compression_methods))
                 goto err;
 
-        if (tls13_client_hello_is_legacy(cbs)) {
+        if (tls13_client_hello_is_legacy(cbs) || s->version < TLS1_3_VERSION) {
                 if (!CBS_skip(cbs, CBS_len(cbs)))
                         goto err;
                 return tls13_use_legacy_server(ctx);