sign_sig: drop ckinv

The only reason ckinv exists is to be able to avoid a copy. This copy
leaks some timing info, that will be mitigated in a subsequent step.
It is an unused or at least uncommonly used codepath.

ok jsing

1 files changed, 7 insertions, 5 deletions

diff --git a/src/lib/libcrypto/ecdsa/ecs_ossl.c b/src/lib/libcrypto/ecdsa/ecs_ossl.c
index d935d237ba..2140f8a8e1 100644
--- a/src/lib/libcrypto/ecdsa/ecs_ossl.c
+++ b/src/lib/libcrypto/ecdsa/ecs_ossl.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ecs_ossl.c,v 1.60 2023/07/03 13:53:54 tb Exp $ */
+/* $OpenBSD: ecs_ossl.c,v 1.61 2023/07/03 14:51:09 tb Exp $ */
 /*
  * Written by Nils Larsch for the OpenSSL project
  */
@@ -274,7 +274,7 @@ ossl_ecdsa_sign_sig(const unsigned char *dgst, int dgst_len,
         BN_CTX *ctx = NULL;
         BIGNUM *kinv = NULL, *r = NULL, *s = NULL;
         BIGNUM *b, *binv, *bm, *bxr, *m;
-        const BIGNUM *ckinv, *order, *priv_key;
+        const BIGNUM *order, *priv_key;
         int caller_supplied_values = 0;
         int attempts = 0;
         ECDSA_SIG *sig = NULL;
@@ -331,7 +331,10 @@ ossl_ecdsa_sign_sig(const unsigned char *dgst, int dgst_len,
                  */
                 caller_supplied_values = 1;
 
-                ckinv = in_kinv;
+                if ((kinv = BN_dup(in_kinv)) == NULL) {
+                        ECDSAerror(ERR_R_MALLOC_FAILURE);
+                        goto err;
+                }
                 if (!bn_copy(r, in_r)) {
                         ECDSAerror(ERR_R_MALLOC_FAILURE);
                         goto err;
@@ -344,7 +347,6 @@ ossl_ecdsa_sign_sig(const unsigned char *dgst, int dgst_len,
                                 ECDSAerror(ERR_R_ECDSA_LIB);
                                 goto err;
                         }
-                        ckinv = kinv;
                 }
 
                 /*
@@ -386,7 +388,7 @@ ossl_ecdsa_sign_sig(const unsigned char *dgst, int dgst_len,
                         ECDSAerror(ERR_R_BN_LIB);
                         goto err;
                 }
-                if (!BN_mod_mul(s, s, ckinv, order, ctx)) { /* s = b(m + xr)k^-1 */
+                if (!BN_mod_mul(s, s, kinv, order, ctx)) { /* s = b(m + xr)k^-1 */
                         ECDSAerror(ERR_R_BN_LIB);
                         goto err;
                 }