Avoid undefined behavior with memcmp(NULL, x, 0) in ASN1_STRING_cmp()

ok jsing miod

1 files changed, 6 insertions, 4 deletions

diff --git a/src/lib/libcrypto/asn1/a_string.c b/src/lib/libcrypto/asn1/a_string.c
index bfd2abf2f7..ca03008186 100644
--- a/src/lib/libcrypto/asn1/a_string.c
+++ b/src/lib/libcrypto/asn1/a_string.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: a_string.c,v 1.14 2023/07/05 21:23:36 beck Exp $ */
+/* $OpenBSD: a_string.c,v 1.15 2023/08/15 17:38:00 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -119,10 +119,12 @@ ASN1_STRING_cmp(const ASN1_STRING *a, const ASN1_STRING *b)
                 return -1;
         if ((cmp = (a->length - b->length)) != 0)
                 return cmp;
-        if ((cmp = memcmp(a->data, b->data, a->length)) != 0)
-                return cmp;
+        if (a->length != 0) {
+                if ((cmp = memcmp(a->data, b->data, a->length)) != 0)
+                        return 0;
+        }
 
-        return (a->type - b->type);
+        return a->type - b->type;
 }
 LCRYPTO_ALIAS(ASN1_STRING_cmp);