Move BN_RECP_CTX to the heap

This introduces a BN_RECP_CTX_create() function that allocates and
populates the BN_RECP_CTX in a single call, without taking an unused
BN_CTX argument.

At the same time, make the N and Nr members BIGNUMs on the heap which
are allocated by BN_RECP_CTX_create() and freed by BN_RECP_CTX_free()
and remove the unnecessary flags argument.

Garbage collect the now unused BN_RECP_CTX_{new,init,set}().

ok jsing

1 files changed, 10 insertions, 12 deletions

diff --git a/src/lib/libcrypto/bn/bn_exp.c b/src/lib/libcrypto/bn/bn_exp.c
index c51296c3c3..8ff518e938 100644
--- a/src/lib/libcrypto/bn/bn_exp.c
+++ b/src/lib/libcrypto/bn/bn_exp.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_exp.c,v 1.53 2024/04/10 14:58:06 beck Exp $ */
+/* $OpenBSD: bn_exp.c,v 1.54 2025/01/21 15:44:22 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -972,7 +972,7 @@ BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
         BIGNUM *aa, *q;
         /* Table of variables obtained from 'ctx' */
         BIGNUM *val[TABLE_SIZE];
-        BN_RECP_CTX recp;
+        BN_RECP_CTX *recp = NULL;
         int ret = 0;
 
         if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
@@ -992,8 +992,6 @@ BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
                 return ret;
         }
 
-        BN_RECP_CTX_init(&recp);
-
         BN_CTX_start(ctx);
         if ((aa = BN_CTX_get(ctx)) == NULL)
                 goto err;
@@ -1007,10 +1005,10 @@ BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
                 if (!bn_copy(aa, m))
                         goto err;
                 aa->neg = 0;
-                if (BN_RECP_CTX_set(&recp, aa, ctx) <= 0)
+                if ((recp = BN_RECP_CTX_create(aa)) == 0)
                         goto err;
         } else {
-                if (BN_RECP_CTX_set(&recp, m, ctx) <= 0)
+                if ((recp = BN_RECP_CTX_create(m)) == 0)
                         goto err;
         }
 
@@ -1025,13 +1023,13 @@ BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
 
         window = BN_window_bits_for_exponent_size(bits);
         if (window > 1) {
-                if (!BN_mod_mul_reciprocal(aa, val[0], val[0], &recp, ctx))
+                if (!BN_mod_mul_reciprocal(aa, val[0], val[0], recp, ctx))
                         goto err;
                 j = 1 << (window - 1);
                 for (i = 1; i < j; i++) {
                         if (((val[i] = BN_CTX_get(ctx)) == NULL) ||
                             !BN_mod_mul_reciprocal(val[i], val[i - 1],
-                            aa, &recp, ctx))
+                            aa, recp, ctx))
                                 goto err;
                 }
         }
@@ -1049,7 +1047,7 @@ BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
         for (;;) {
                 if (BN_is_bit_set(q, wstart) == 0) {
                         if (!start)
-                                if (!BN_mod_mul_reciprocal(r, r, r, &recp, ctx))
+                                if (!BN_mod_mul_reciprocal(r, r, r, recp, ctx))
                                         goto err;
                         if (wstart == 0)
                                 break;
@@ -1078,12 +1076,12 @@ BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
                 /* add the 'bytes above' */
                 if (!start)
                         for (i = 0; i < j; i++) {
-                                if (!BN_mod_mul_reciprocal(r, r, r, &recp, ctx))
+                                if (!BN_mod_mul_reciprocal(r, r, r, recp, ctx))
                                         goto err;
                         }
 
                 /* wvalue will be an odd number < 2^window */
-                if (!BN_mod_mul_reciprocal(r, r, val[wvalue >> 1], &recp, ctx))
+                if (!BN_mod_mul_reciprocal(r, r, val[wvalue >> 1], recp, ctx))
                         goto err;
 
                 /* move the 'window' down further */
@@ -1099,7 +1097,7 @@ BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
 
  err:
         BN_CTX_end(ctx);
-        BN_RECP_CTX_free(&recp);
+        BN_RECP_CTX_free(recp);
 
         return ret;
 }