Avoid memcmp(NULL, x, 0) in OBJ_cmp()

If a->length is 0, either a->data or b->data could be NULL and memcmp()
will rely on undefined behavior to compare them as equal. So avoid this
comparison in the first place.

ok jsing

diff --git a/lib/libcrypto/objects/obj_lib.c b/lib/libcrypto/objects/obj_lib.c
index 83575c1..45062db 100644 (file)
--- a/lib/libcrypto/objects/obj_lib.c
+++ b/lib/libcrypto/objects/obj_lib.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: obj_lib.c,v 1.18 2023/07/08 12:27:51 beck Exp $ */
+/* $OpenBSD: obj_lib.c,v 1.19 2023/08/17 09:13:01 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -124,11 +124,12 @@ LCRYPTO_ALIAS(OBJ_dup);
 int
 OBJ_cmp(const ASN1_OBJECT *a, const ASN1_OBJECT *b)
 {
-       int ret;
+       int cmp;
 
-       ret = (a->length - b->length);
-       if (ret)
-               return (ret);
-       return (memcmp(a->data, b->data, a->length));
+       if ((cmp = a->length - b->length) != 0)
+               return cmp;
+       if (a->length == 0)
+               return 0;
+       return memcmp(a->data, b->data, a->length);
 }
 LCRYPTO_ALIAS(OBJ_cmp);