Cast int64_t to uint64_t before negating.

Avoid undefined behaviour/integer overflow by casting an int64_t to
uint64_t before negating.

Fixes oss-fuzz #49043

ok tb@

1 files changed, 7 insertions, 3 deletions

diff --git a/src/lib/libcrypto/asn1/a_int.c b/src/lib/libcrypto/asn1/a_int.c
index 1f1e587d39..d7790c787d 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 1.43 2022/07/09 14:46:42 tb Exp $ */
+/* $OpenBSD: a_int.c,v 1.44 2022/07/13 20:07:44 jsing Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -282,14 +282,18 @@ ASN1_INTEGER_get_int64(int64_t *out_val, const ASN1_INTEGER *aint)
 int
 ASN1_INTEGER_set_int64(ASN1_INTEGER *aint, int64_t val)
 {
+        uint64_t uval;
+
         asn1_aint_clear(aint);
 
+        uval = (uint64_t)val;
+
         if (val < 0) {
                 aint->type = V_ASN1_NEG_INTEGER;
-                val = -val;
+                uval = -uval;
         }
 
-        return asn1_aint_set_uint64((uint64_t)val, &aint->data, &aint->length);
+        return asn1_aint_set_uint64(uval, &aint->data, &aint->length);
 }
 
 long