From c6e3089538d69e8e70c037404ec0d7cb5bcece4d Mon Sep 17 00:00:00 2001
From: jsing <>
Date: Tue, 14 Feb 2023 18:22:35 +0000
Subject: Make BN_is_zero() check word values.

Rather than completely relying on top, check the words of a bignum.
This gets us one step away from being dependent on top and additionally
means that we correctly report zero even if top is not yet correct.

ok tb@
---
 src/lib/libcrypto/bn/bn_lib.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

(limited to 'src')

diff --git a/src/lib/libcrypto/bn/bn_lib.c b/src/lib/libcrypto/bn/bn_lib.c
index b792250fbc..89e2713a0f 100644
--- a/src/lib/libcrypto/bn/bn_lib.c
+++ b/src/lib/libcrypto/bn/bn_lib.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_lib.c,v 1.75 2023/02/14 18:06:06 jsing Exp $ */
+/* $OpenBSD: bn_lib.c,v 1.76 2023/02/14 18:22:35 jsing Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -252,7 +252,6 @@ BN_num_bits(const BIGNUM *a)
 {
 	int i = a->top - 1;
 
-
 	if (BN_is_zero(a))
 		return 0;
 	return ((i * BN_BITS2) + BN_num_bits_word(a->d[i]));
@@ -917,9 +916,15 @@ BN_abs_is_word(const BIGNUM *a, const BN_ULONG w)
 }
 
 int
-BN_is_zero(const BIGNUM *a)
+BN_is_zero(const BIGNUM *bn)
 {
-	return a->top == 0;
+	BN_ULONG bits = 0;
+	int i;
+
+	for (i = 0; i < bn->top; i++)
+		bits |= bn->d[i];
+
+	return bits == 0;
 }
 
 int
-- 
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