Provide BN_zero()/BN_one() as functions and make BN_zero() always succeed.

BN_zero() is currently implemented using BN_set_word(), which means it can
fail, however almost nothing ever checks the return value. A long time
ago OpenSSL changed BN_zero() to always succeed and return void, however
kept BN_zero as a macro that calls a new BN_zero_ex() function, so that
it can be switched back to the "can fail" version.

Take a simpler approach - change BN_zero()/BN_one() to functions and make
BN_zero() always succeed. This will be exposed in the next bump, at which
point we can hopefully also remove the BN_zero_ex() function.

ok tb@

3 files changed, 22 insertions, 7 deletions

diff --git a/src/lib/libcrypto/bn/bn.h b/src/lib/libcrypto/bn/bn.h
index bef0a878e2..ba6c25ba0a 100644
--- a/src/lib/libcrypto/bn/bn.h
+++ b/src/lib/libcrypto/bn/bn.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn.h,v 1.56 2022/11/30 01:47:19 jsing Exp $ */
+/* $OpenBSD: bn.h,v 1.57 2022/12/17 15:56:25 jsing Exp $ */
 /* Copyright (C) 1995-1997 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -329,6 +329,10 @@ int BN_is_one(const BIGNUM *a);
 int BN_is_word(const BIGNUM *a, const BN_ULONG w);
 int BN_is_odd(const BIGNUM *a);
 
+#if defined(LIBRESSL_INTERNAL) || defined(LIBRESSL_NEXT_API)
+void BN_zero(BIGNUM *a);
+int BN_one(BIGNUM *a);
+#else
 #define BN_one(a)       BN_set_word((a), 1)
 
 void BN_zero_ex(BIGNUM *a);
@@ -338,6 +342,7 @@ void BN_zero_ex(BIGNUM *a);
 #else
 #define BN_zero(a)      (BN_set_word((a),0))
 #endif
+#endif
 
 const BIGNUM *BN_value_one(void);
 char *  BN_options(void);
diff --git a/src/lib/libcrypto/bn/bn_isqrt.c b/src/lib/libcrypto/bn/bn_isqrt.c
index 81f90b10be..ec77e1b078 100644
--- a/src/lib/libcrypto/bn/bn_isqrt.c
+++ b/src/lib/libcrypto/bn/bn_isqrt.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: bn_isqrt.c,v 1.5 2022/12/01 21:59:54 tb Exp $ */
+/*      $OpenBSD: bn_isqrt.c,v 1.6 2022/12/17 15:56:25 jsing Exp $ */
 /*
  * Copyright (c) 2022 Theo Buehler <tb@openbsd.org>
  *
@@ -74,8 +74,7 @@ bn_isqrt(BIGNUM *out_sqrt, int *out_perfect, const BIGNUM *n, BN_CTX *in_ctx)
 
         if (BN_is_zero(n)) {
                 perfect = 1;
-                if (!BN_zero(a))
-                        goto err;
+                BN_zero(a);
                 goto done;
         }
 
diff --git a/src/lib/libcrypto/bn/bn_lib.c b/src/lib/libcrypto/bn/bn_lib.c
index 851c337ef0..c47f2fa024 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 1.66 2022/11/30 03:08:39 jsing Exp $ */
+/* $OpenBSD: bn_lib.c,v 1.67 2022/12/17 15:56:25 jsing Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -998,11 +998,22 @@ BN_swap_ct(BN_ULONG condition, BIGNUM *a, BIGNUM *b, size_t nwords)
 }
 
 void
-BN_zero_ex(BIGNUM *a)
+BN_zero(BIGNUM *a)
 {
         a->neg = 0;
         a->top = 0;
-        /* XXX: a->flags &= ~BN_FIXED_TOP */
+}
+
+void
+BN_zero_ex(BIGNUM *a)
+{
+        BN_zero(a);
+}
+
+int
+BN_one(BIGNUM *a)
+{
+        return BN_set_word(a, 1);
 }
 
 int