Avoid clobbering the error code when sending an alert

In order to fail gracefully on encountering a self-signed cert, curl looks
at the top-most error on the stack and needs specific SSL_R_ error codes.
This mechanism was broken when the tls13_alert_sent_cb() was added after
people complained about unhelpful unknown errors. Fix this by only setting
the error code from a fatal alert if no error has been set previously.

Issue reported by Christopher Reid

ok jsing

1 files changed, 3 insertions, 2 deletions

diff --git a/src/lib/libssl/tls13_lib.c b/src/lib/libssl/tls13_lib.c
index 9dbb7d6430..f064521c8b 100644
--- a/src/lib/libssl/tls13_lib.c
+++ b/src/lib/libssl/tls13_lib.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: tls13_lib.c,v 1.58 2021/03/21 18:36:34 jsing Exp $ */
+/*      $OpenBSD: tls13_lib.c,v 1.59 2021/04/07 21:48:23 tb Exp $ */
 /*
  * Copyright (c) 2018, 2019 Joel Sing <jsing@openbsd.org>
  * Copyright (c) 2019 Bob Beck <beck@openbsd.org>
@@ -147,7 +147,8 @@ tls13_alert_sent_cb(uint8_t alert_desc, void *arg)
         }
 
         /* All other alerts are treated as fatal in TLSv1.3. */
-        SSLerror(ctx->ssl, SSL_AD_REASON_OFFSET + alert_desc);
+        if (ctx->error.code == 0)
+                SSLerror(ctx->ssl, SSL_AD_REASON_OFFSET + alert_desc);
 }
 
 static void