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, 16 insertions, 6 deletions

diff --git a/src/lib/libssl/ssl_kex.c b/src/lib/libssl/ssl_kex.c
index 78b528b168..cd6713b8b2 100644
--- a/src/lib/libssl/ssl_kex.c
+++ b/src/lib/libssl/ssl_kex.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_kex.c,v 1.8 2021/12/04 14:03:22 jsing Exp $ */
+/* $OpenBSD: ssl_kex.c,v 1.9 2022/01/11 18:28:41 jsing Exp $ */
 /*
  * Copyright (c) 2020, 2021 Joel Sing <jsing@openbsd.org>
  *
@@ -156,18 +156,24 @@ ssl_kex_public_dhe(DH *dh, CBB *cbb)
 }
 
 int
-ssl_kex_peer_params_dhe(DH *dh, CBS *cbs, int *invalid_params)
+ssl_kex_peer_params_dhe(DH *dh, CBS *cbs, int *decode_error,
+    int *invalid_params)
 {
         BIGNUM *p = NULL, *g = NULL;
         CBS dh_p, dh_g;
         int ret = 0;
 
+        *decode_error = 0;
         *invalid_params = 0;
 
-        if (!CBS_get_u16_length_prefixed(cbs, &dh_p))
+        if (!CBS_get_u16_length_prefixed(cbs, &dh_p)) {
+                *decode_error = 1;
                 goto err;
-        if (!CBS_get_u16_length_prefixed(cbs, &dh_g))
+        }
+        if (!CBS_get_u16_length_prefixed(cbs, &dh_g)) {
+                *decode_error = 1;
                 goto err;
+        }
 
         if ((p = BN_bin2bn(CBS_data(&dh_p), CBS_len(&dh_p), NULL)) == NULL)
                 goto err;
@@ -194,17 +200,21 @@ ssl_kex_peer_params_dhe(DH *dh, CBS *cbs, int *invalid_params)
 }
 
 int
-ssl_kex_peer_public_dhe(DH *dh, CBS *cbs, int *invalid_key)
+ssl_kex_peer_public_dhe(DH *dh, CBS *cbs, int *decode_error,
+    int *invalid_key)
 {
         BIGNUM *pub_key = NULL;
         int check_flags;
         CBS dh_y;
         int ret = 0;
 
+        *decode_error = 0;
         *invalid_key = 0;
 
-        if (!CBS_get_u16_length_prefixed(cbs, &dh_y))
+        if (!CBS_get_u16_length_prefixed(cbs, &dh_y)) {
+                *decode_error = 1;
                 goto err;
+        }
 
         if ((pub_key = BN_bin2bn(CBS_data(&dh_y), CBS_len(&dh_y),
             NULL)) == NULL)