Handle BN_CTX at the EC API boundary.

The EC API allows callers to optionally pass in a BN_CTX, which means that
any code needing a BN_CTX has to check if one was provided, allocate one if
not, then free it again. Rather than doing this dance throughout the EC
code, handle the BN_CTX existance at the EC API boundary. This means that
lower level implementation code can simply assume that the BN_CTX is
available.

ok tb@

1 files changed, 21 insertions, 41 deletions

diff --git a/src/lib/libcrypto/ec/ecp_oct.c b/src/lib/libcrypto/ec/ecp_oct.c
index f2f1929e84..8cdf544bf1 100644
--- a/src/lib/libcrypto/ec/ecp_oct.c
+++ b/src/lib/libcrypto/ec/ecp_oct.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ecp_oct.c,v 1.19 2022/11/26 16:08:52 tb Exp $ */
+/* $OpenBSD: ecp_oct.c,v 1.20 2023/04/11 18:58:20 jsing Exp $ */
 /* Includes code written by Lenka Fibikova <fibikova@exp-math.uni-essen.de>
  * for the OpenSSL project.
  * Includes code written by Bodo Moeller for the OpenSSL project.
@@ -70,21 +70,16 @@ int
 ec_GFp_simple_set_compressed_coordinates(const EC_GROUP *group,
     EC_POINT *point, const BIGNUM *x_, int y_bit, BN_CTX *ctx)
 {
-        BN_CTX *new_ctx = NULL;
         BIGNUM *tmp1, *tmp2, *x, *y;
         int ret = 0;
 
         /* clear error queue */
         ERR_clear_error();
 
-        if (ctx == NULL) {
-                ctx = new_ctx = BN_CTX_new();
-                if (ctx == NULL)
-                        return 0;
-        }
         y_bit = (y_bit != 0);
 
         BN_CTX_start(ctx);
+
         if ((tmp1 = BN_CTX_get(ctx)) == NULL)
                 goto err;
         if ((tmp2 = BN_CTX_get(ctx)) == NULL)
@@ -179,27 +174,25 @@ ec_GFp_simple_set_compressed_coordinates(const EC_GROUP *group,
 
  err:
         BN_CTX_end(ctx);
-        BN_CTX_free(new_ctx);
+
         return ret;
 }
 
-
 size_t
-ec_GFp_simple_point2oct(const EC_GROUP *group, const EC_POINT *point, point_conversion_form_t form,
-    unsigned char *buf, size_t len, BN_CTX *ctx)
+ec_GFp_simple_point2oct(const EC_GROUP *group, const EC_POINT *point,
+    point_conversion_form_t form, unsigned char *buf, size_t len, BN_CTX *ctx)
 {
-        size_t ret;
-        BN_CTX *new_ctx = NULL;
-        int used_ctx = 0;
         BIGNUM *x, *y;
         size_t field_len, i, skip;
+        size_t ret = 0;
 
-        if ((form != POINT_CONVERSION_COMPRESSED)
-            && (form != POINT_CONVERSION_UNCOMPRESSED)
-            && (form != POINT_CONVERSION_HYBRID)) {
+        if (form != POINT_CONVERSION_COMPRESSED &&
+            form != POINT_CONVERSION_UNCOMPRESSED &&
+            form != POINT_CONVERSION_HYBRID) {
                 ECerror(EC_R_INVALID_FORM);
-                goto err;
+                return 0;
         }
+
         if (EC_POINT_is_at_infinity(group, point) > 0) {
                 /* encodes to a single 0 octet */
                 if (buf != NULL) {
@@ -211,23 +204,20 @@ ec_GFp_simple_point2oct(const EC_GROUP *group, const EC_POINT *point, point_conv
                 }
                 return 1;
         }
+
         /* ret := required output buffer length */
         field_len = BN_num_bytes(&group->field);
         ret = (form == POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
 
+        BN_CTX_start(ctx);
+
         /* if 'buf' is NULL, just return required length */
         if (buf != NULL) {
                 if (len < ret) {
                         ECerror(EC_R_BUFFER_TOO_SMALL);
                         goto err;
                 }
-                if (ctx == NULL) {
-                        ctx = new_ctx = BN_CTX_new();
-                        if (ctx == NULL)
-                                return 0;
-                }
-                BN_CTX_start(ctx);
-                used_ctx = 1;
+
                 if ((x = BN_CTX_get(ctx)) == NULL)
                         goto err;
                 if ((y = BN_CTX_get(ctx)) == NULL)
@@ -276,18 +266,12 @@ ec_GFp_simple_point2oct(const EC_GROUP *group, const EC_POINT *point, point_conv
                         goto err;
                 }
         }
-        if (used_ctx)
-                BN_CTX_end(ctx);
-        BN_CTX_free(new_ctx);
-        return ret;
 
  err:
-        if (used_ctx)
-                BN_CTX_end(ctx);
-        BN_CTX_free(new_ctx);
-        return 0;
-}
+        BN_CTX_end(ctx);
 
+        return ret;
+}
 
 int
 ec_GFp_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
@@ -295,7 +279,6 @@ ec_GFp_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
 {
         point_conversion_form_t form;
         int y_bit;
-        BN_CTX *new_ctx = NULL;
         BIGNUM *x, *y;
         size_t field_len, enc_len;
         int ret = 0;
@@ -331,12 +314,9 @@ ec_GFp_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
                 ECerror(EC_R_INVALID_ENCODING);
                 return 0;
         }
-        if (ctx == NULL) {
-                ctx = new_ctx = BN_CTX_new();
-                if (ctx == NULL)
-                        return 0;
-        }
+
         BN_CTX_start(ctx);
+
         if ((x = BN_CTX_get(ctx)) == NULL)
                 goto err;
         if ((y = BN_CTX_get(ctx)) == NULL)
@@ -380,6 +360,6 @@ ec_GFp_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
 
  err:
         BN_CTX_end(ctx);
-        BN_CTX_free(new_ctx);
+
         return ret;
 }