Encode an ASN.1 INTEGER with NULL data to value of zero.

When an ASN1_INTEGER is created it has NULL data until a value is set -
previously, an ASN1_INTEGER in this state encoded to an ASN.1 INTEGER with
a value of 0, rather than being treated as an error. While code should
really set values, the historical behaviour has not required this.

Found the hard way by sthen@ with acme-client.

ok tb@

1 files changed, 4 insertions, 2 deletions

diff --git a/src/lib/libcrypto/asn1/a_int.c b/src/lib/libcrypto/asn1/a_int.c
index 6a24c5183c..1f4778922d 100644
--- a/src/lib/libcrypto/asn1/a_int.c
+++ b/src/lib/libcrypto/asn1/a_int.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: a_int.c,v 1.45 2022/08/20 18:17:33 jsing Exp $ */
+/* $OpenBSD: a_int.c,v 1.46 2022/08/28 17:49:25 jsing Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -553,7 +553,9 @@ i2c_ASN1_INTEGER_cbb(ASN1_INTEGER *aint, CBB *cbb)
         CBS cbs;
         int ret = 0;
 
-        if (aint->data == NULL || aint->length < 0)
+        if (aint->length < 0)
+                goto err;
+        if (aint->data == NULL && aint->length != 0)
                 goto err;
 
         if ((aint->type & ~V_ASN1_NEG) != V_ASN1_ENUMERATED &&