Clean up ec_asn1_group2fieldid()

This drops some unnecessary freeing that was turned into a double free
reachable via public API in OpenSSL 1.1. Other than that it unindents
code and uses better variable names.

ok jsing

1 files changed, 28 insertions, 32 deletions

diff --git a/src/lib/libcrypto/ec/ec_asn1.c b/src/lib/libcrypto/ec/ec_asn1.c
index 3cc91fe4c1..291b59ac06 100644
--- a/src/lib/libcrypto/ec/ec_asn1.c
+++ b/src/lib/libcrypto/ec/ec_asn1.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ec_asn1.c,v 1.66 2024/10/11 18:35:39 tb Exp $ */
+/* $OpenBSD: ec_asn1.c,v 1.67 2024/10/11 18:55:44 tb Exp $ */
 /*
  * Written by Nils Larsch for the OpenSSL project.
  */
@@ -559,50 +559,46 @@ EC_PRIVATEKEY_free(EC_PRIVATEKEY *a)
 static int
 ec_asn1_group2fieldid(const EC_GROUP *group, X9_62_FIELDID *field)
 {
-        int ok = 0, nid;
-        BIGNUM *tmp = NULL;
+        BIGNUM *p = NULL;
+        int nid;
+        int ret = 0;
 
         if (group == NULL || field == NULL)
-                return 0;
-
-        /* clear the old values (if necessary) */
-        if (field->fieldType != NULL)
-                ASN1_OBJECT_free(field->fieldType);
-        if (field->p.other != NULL)
-                ASN1_TYPE_free(field->p.other);
+                goto err;
 
         nid = EC_METHOD_get_field_type(EC_GROUP_method_of(group));
-        /* set OID for the field */
+        if (nid == NID_X9_62_characteristic_two_field) {
+                ECerror(EC_R_GF2M_NOT_SUPPORTED);
+                goto err;
+        }
+        if (nid != NID_X9_62_prime_field) {
+                ECerror(EC_R_INVALID_FIELD);
+                goto err;
+        }
+
         if ((field->fieldType = OBJ_nid2obj(nid)) == NULL) {
                 ECerror(ERR_R_OBJ_LIB);
                 goto err;
         }
-        if (nid == NID_X9_62_prime_field) {
-                if ((tmp = BN_new()) == NULL) {
-                        ECerror(ERR_R_MALLOC_FAILURE);
-                        goto err;
-                }
-                /* the parameters are specified by the prime number p */
-                if (!EC_GROUP_get_curve(group, tmp, NULL, NULL, NULL)) {
-                        ECerror(ERR_R_EC_LIB);
-                        goto err;
-                }
-                /* set the prime number */
-                field->p.prime = BN_to_ASN1_INTEGER(tmp, NULL);
-                if (field->p.prime == NULL) {
-                        ECerror(ERR_R_ASN1_LIB);
-                        goto err;
-                }
-        } else {
-                ECerror(EC_R_GF2M_NOT_SUPPORTED);
+        if ((p = BN_new()) == NULL) {
+                ECerror(ERR_R_MALLOC_FAILURE);
+                goto err;
+        }
+        if (!EC_GROUP_get_curve(group, p, NULL, NULL, NULL)) {
+                ECerror(ERR_R_EC_LIB);
+                goto err;
+        }
+        if ((field->p.prime = BN_to_ASN1_INTEGER(p, NULL)) == NULL) {
+                ECerror(ERR_R_ASN1_LIB);
                 goto err;
         }
 
-        ok = 1;
+        ret = 1;
 
  err:
-        BN_free(tmp);
-        return (ok);
+        BN_free(p);
+
+        return ret;
 }
 
 static int