From: Billy Brumley <bbrumley@gmail.com>
Date: Thu, 9 Jun 2022 21:03:23 +0000 (+0300)
Subject: [crypto/bn] BN_consttime_swap: remove superfluous early exit
X-Git-Tag: openssl-3.2.0-alpha1~2541
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a644cb7c1c19c78e2ca393c8ca36989e7ca61715;p=thirdparty%2Fopenssl.git

[crypto/bn] BN_consttime_swap: remove superfluous early exit

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18518)
---

diff --git a/crypto/bn/bn_lib.c b/crypto/bn/bn_lib.c
index 23a4415fb9f..089b23963d2 100644
--- a/crypto/bn/bn_lib.c
+++ b/crypto/bn/bn_lib.c
@@ -910,9 +910,6 @@ void BN_consttime_swap(BN_ULONG condition, BIGNUM *a, BIGNUM *b, int nwords)
     BN_ULONG t;
     int i;
 
-    if (a == b)
-        return;
-
     bn_wcheck_size(a, nwords);
     bn_wcheck_size(b, nwords);
 
diff --git a/test/bntest.c b/test/bntest.c
index 9f4bc0b3eb5..85445b701b1 100644
--- a/test/bntest.c
+++ b/test/bntest.c
@@ -171,6 +171,11 @@ static int test_swap(void)
             || !equalBN("swap", b, c))
         goto err;
 
+    /* regular swap: same pointer */
+    BN_swap(a, a);
+    if (!equalBN("swap with same pointer", a, d))
+        goto err;
+
     /* conditional swap: true */
     cond = 1;
     BN_consttime_swap(cond, a, b, top);
@@ -178,6 +183,11 @@ static int test_swap(void)
             || !equalBN("cswap true", b, d))
         goto err;
 
+    /* conditional swap: true, same pointer */
+    BN_consttime_swap(cond, a, a, top);
+    if (!equalBN("cswap true", a, c))
+        goto err;
+
     /* conditional swap: false */
     cond = 0;
     BN_consttime_swap(cond, a, b, top);
@@ -185,6 +195,11 @@ static int test_swap(void)
             || !equalBN("cswap false", b, d))
         goto err;
 
+    /* conditional swap: false, same pointer */
+    BN_consttime_swap(cond, a, a, top);
+    if (!equalBN("cswap false", a, c))
+        goto err;
+
     /* same tests but checking flag swap */
     BN_set_flags(a, BN_FLG_CONSTTIME);