From f6b6cc33007e6d3d1d9d24955ba7783b71bb73c4 Mon Sep 17 00:00:00 2001
From: jsing <jsing@openbsd.org>
Date: Wed, 11 Jan 2023 04:35:26 +0000
Subject: [PATCH] Simplify BIGNUM handling in dsa_builtin_keygen().

Rather than having complicated "attempt to reuse" dances, always allocate
priv_key/pub_key, then free and assign on success.

ok tb@
---
 lib/libcrypto/dsa/dsa_key.c | 35 +++++++++++++++++------------------
 1 file changed, 17 insertions(+), 18 deletions(-)

diff --git a/lib/libcrypto/dsa/dsa_key.c b/lib/libcrypto/dsa/dsa_key.c
index 051c8127811..890f991df9f 100644
--- a/lib/libcrypto/dsa/dsa_key.c
+++ b/lib/libcrypto/dsa/dsa_key.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: dsa_key.c,v 1.32 2022/11/26 16:08:52 tb Exp $ */
+/* $OpenBSD: dsa_key.c,v 1.33 2023/01/11 04:35:26 jsing Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -82,39 +82,38 @@ DSA_generate_key(DSA *dsa)
 static int
 dsa_builtin_keygen(DSA *dsa)
 {
-	int ok = 0;
-	BN_CTX *ctx = NULL;
 	BIGNUM *pub_key = NULL, *priv_key = NULL;
+	BN_CTX *ctx = NULL;
+	int ok = 0;
 
-	if ((ctx = BN_CTX_new()) == NULL)
+	if ((priv_key = BN_new()) == NULL)
+		goto err;
+	if ((pub_key = BN_new()) == NULL)
 		goto err;
 
-	if ((priv_key = dsa->priv_key) == NULL) {
-		if ((priv_key = BN_new()) == NULL)
-			goto err;
-	}
+	if ((ctx = BN_CTX_new()) == NULL)
+		goto err;
 
 	if (!bn_rand_interval(priv_key, BN_value_one(), dsa->q))
 		goto err;
-
-	if ((pub_key = dsa->pub_key) == NULL) {
-		if ((pub_key = BN_new()) == NULL)
-			goto err;
-	}
-
 	if (!BN_mod_exp_ct(pub_key, dsa->g, priv_key, dsa->p, ctx))
 		goto err;
 
+	BN_free(dsa->priv_key);
 	dsa->priv_key = priv_key;
+	priv_key = NULL;
+
+	BN_free(dsa->pub_key);
 	dsa->pub_key = pub_key;
+	pub_key = NULL;
+
 	ok = 1;
 
  err:
-	if (dsa->pub_key == NULL)
-		BN_free(pub_key);
-	if (dsa->priv_key == NULL)
-		BN_free(priv_key);
+	BN_free(pub_key);
+	BN_free(priv_key);
 	BN_CTX_free(ctx);
+
 	return ok;
 }
 #endif
-- 
2.20.1