From 8bbb1196379de707bb70e7d4ef92d3d214ec58bb Mon Sep 17 00:00:00 2001
From: tb <>
Date: Sun, 26 Dec 2021 15:16:50 +0000
Subject: Consistently call BN_init() before BN_with_flags()

BN_with_flags() preserves the BN_FLG_MALLOCED flag of the destination
which results in a potential use of an uninitialized bit. In practice
this doesn't matter since we don't free the cloned BIGNUMs anyway.

As jsing points out, these are mostly pointless noise and should be
garbage collected. I'll leave that for another rainy day.

Coverity flagged one instance BN_gcd_no_branch(), the rest was found by
the ever so helpful grep(1).

CID 345122

ok jsing
---
 src/lib/libcrypto/bn/bn_gcd.c | 40 +++++++++++++++++++++++++++-------------
 1 file changed, 27 insertions(+), 13 deletions(-)

(limited to 'src/lib/libcrypto/bn')

diff --git a/src/lib/libcrypto/bn/bn_gcd.c b/src/lib/libcrypto/bn/bn_gcd.c
index 469ae752fb..d756398c8f 100644
--- a/src/lib/libcrypto/bn/bn_gcd.c
+++ b/src/lib/libcrypto/bn/bn_gcd.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_gcd.c,v 1.15 2017/01/29 17:49:22 beck Exp $ */
+/* $OpenBSD: bn_gcd.c,v 1.16 2021/12/26 15:16:50 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -576,6 +576,9 @@ BN_mod_inverse_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
 	bn_check_top(a);
 	bn_check_top(n);
 
+	BN_init(&local_A);
+	BN_init(&local_B);
+
 	BN_CTX_start(ctx);
 	if ((A = BN_CTX_get(ctx)) == NULL)
 		goto err;
@@ -608,10 +611,12 @@ BN_mod_inverse_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
 	A->neg = 0;
 
 	if (B->neg || (BN_ucmp(B, A) >= 0)) {
-		/* Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
-	 	 * BN_div_no_branch will be called eventually.
-	 	 */
+		/*
+		 * Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
+		 * BN_div_no_branch will be called eventually.
+		 */
 		pB = &local_B;
+		/* BN_init() done at the top of the function. */
 		BN_with_flags(pB, B, BN_FLG_CONSTTIME);
 		if (!BN_nnmod(B, pB, A, ctx))
 			goto err;
@@ -633,10 +638,12 @@ BN_mod_inverse_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
 		 *      sign*Y*a  ==  A   (mod |n|)
 		 */
 
-		/* Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
-	 	 * BN_div_no_branch will be called eventually.
-	 	 */
+		/*
+		 * Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
+		 * BN_div_no_branch will be called eventually.
+		 */
 		pA = &local_A;
+		/* BN_init() done at the top of the function. */
 		BN_with_flags(pA, A, BN_FLG_CONSTTIME);
 
 		/* (D, M) := (A/B, A%B) ... */
@@ -740,6 +747,9 @@ BN_gcd_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
 		goto err;
 	R = in;
 
+	BN_init(&local_A);
+	BN_init(&local_B);
+
 	bn_check_top(a);
 	bn_check_top(n);
 
@@ -768,10 +778,12 @@ BN_gcd_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
 	A->neg = 0;
 
 	if (B->neg || (BN_ucmp(B, A) >= 0)) {
-		/* Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
-	 	 * BN_div_no_branch will be called eventually.
-	 	 */
+		/*
+		 * Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
+		 * BN_div_no_branch will be called eventually.
+		 */
 		pB = &local_B;
+		/* BN_init() done at the top of the function. */
 		BN_with_flags(pB, B, BN_FLG_CONSTTIME);
 		if (!BN_nnmod(B, pB, A, ctx))
 			goto err;
@@ -793,10 +805,12 @@ BN_gcd_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
 		 *      sign*Y*a  ==  A   (mod |n|)
 		 */
 
-		/* Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
-	 	 * BN_div_no_branch will be called eventually.
-	 	 */
+		/*
+		 * Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
+		 * BN_div_no_branch will be called eventually.
+		 */
 		pA = &local_A;
+		/* BN_init() done at the top of the function. */
 		BN_with_flags(pA, A, BN_FLG_CONSTTIME);
 
 		/* (D, M) := (A/B, A%B) ... */
-- 
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