Avoid duplicate default CApath lookups

Fixes #21067

crypto/x509/by_store.c

@@ -111,14 +111,7 @@ static int by_store_ctrl_ex(X509_LOOKUP *ctx, int cmd, const char *argp,
 {
     switch (cmd) {
     case X509_L_ADD_STORE:
-        /* If no URI is given, use the default cert dir as default URI */
-        if (argp == NULL)
-            argp = ossl_safe_getenv(X509_get_default_cert_dir_env());
-
-        if (argp == NULL)
-            argp = X509_get_default_cert_dir();
-
-        {
+        if (argp != NULL) {
             STACK_OF(OPENSSL_STRING) *uris = X509_LOOKUP_get_method_data(ctx);
             char *data = OPENSSL_strdup(argp);
 
@@ -131,12 +124,15 @@ static int by_store_ctrl_ex(X509_LOOKUP *ctx, int cmd, const char *argp,
             }
             return sk_OPENSSL_STRING_push(uris, data) > 0;
         }
+        /* NOP if no URI is given. */
+        return 1;
     case X509_L_LOAD_STORE:
         /* This is a shortcut for quick loading of specific containers */
         return cache_objects(ctx, argp, NULL, 0, libctx, propq);
+    default:
+        /* Unsupported command */
+        return 0;
     }
-
-    return 0;
 }
 
 static int by_store_ctrl(X509_LOOKUP *ctx, int cmd,

crypto/x509/x509_d2.c

@@ -30,6 +30,11 @@ int X509_STORE_set_default_paths_ex(X509_STORE *ctx, OSSL_LIB_CTX *libctx,
     lookup = X509_STORE_add_lookup(ctx, X509_LOOKUP_store());
     if (lookup == NULL)
         return 0;
+    /*
+     * The NULL URI argument will activate any default URIs (presently none),
+     * DO NOT pass the default CApath or CAfile, they're already handled above,
+     * likely much more efficiently.
+     */
     X509_LOOKUP_add_store_ex(lookup, NULL, libctx, propq);
 
     /* clear any errors */