Plumb decode errors through key share parsing code.

Distinguish between decode errors and other errors, so that we can send
a SSL_AD_DECODE_ERROR alert when appropriate.

Fixes a tlsfuzzer failure, due to it expecting a decode error alert and
not receiving one.

Prompted by anton@

ok tb@

1 files changed, 11 insertions, 3 deletions

diff --git a/src/lib/libssl/ssl_tlsext.c b/src/lib/libssl/ssl_tlsext.c
index 7538efdc8c..69f8ddbc40 100644
--- a/src/lib/libssl/ssl_tlsext.c
+++ b/src/lib/libssl/ssl_tlsext.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_tlsext.c,v 1.107 2022/01/11 18:24:03 jsing Exp $ */
+/* $OpenBSD: ssl_tlsext.c,v 1.108 2022/01/11 18:28:41 jsing Exp $ */
 /*
  * Copyright (c) 2016, 2017, 2019 Joel Sing <jsing@openbsd.org>
  * Copyright (c) 2017 Doug Hogan <doug@openbsd.org>
@@ -1478,6 +1478,7 @@ int
 tlsext_keyshare_server_parse(SSL *s, uint16_t msg_type, CBS *cbs, int *alert)
 {
         CBS client_shares, key_exchange;
+        int decode_error;
         uint16_t group;
 
         if (!CBS_get_u16_length_prefixed(cbs, &client_shares))
@@ -1515,8 +1516,11 @@ tlsext_keyshare_server_parse(SSL *s, uint16_t msg_type, CBS *cbs, int *alert)
                         return 0;
                 }
                 if (!tls_key_share_peer_public(S3I(s)->hs.key_share,
-                    &key_exchange, NULL))
+                    &key_exchange, &decode_error, NULL)) {
+                        if (!decode_error)
+                                *alert = SSL_AD_INTERNAL_ERROR;
                         return 0;
+                }
         }
 
         return 1;
@@ -1561,6 +1565,7 @@ int
 tlsext_keyshare_client_parse(SSL *s, uint16_t msg_type, CBS *cbs, int *alert)
 {
         CBS key_exchange;
+        int decode_error;
         uint16_t group;
 
         /* Unpack server share. */
@@ -1588,8 +1593,11 @@ tlsext_keyshare_client_parse(SSL *s, uint16_t msg_type, CBS *cbs, int *alert)
                 return 0;
         }
         if (!tls_key_share_peer_public(S3I(s)->hs.key_share,
-            &key_exchange, NULL))
+            &key_exchange, &decode_error, NULL)) {
+                if (!decode_error)
+                        *alert = SSL_AD_INTERNAL_ERROR;
                 return 0;
+        }
 
         return 1;
 }