From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 98820C3B187 for ; Wed, 12 Feb 2020 20:18:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 717B324677 for ; Wed, 12 Feb 2020 20:18:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728962AbgBLUS1 (ORCPT ); Wed, 12 Feb 2020 15:18:27 -0500 Received: from 216-12-86-13.cv.mvl.ntelos.net ([216.12.86.13]:50546 "EHLO brightrain.aerifal.cx" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728887AbgBLUS1 (ORCPT ); Wed, 12 Feb 2020 15:18:27 -0500 Received: from dalias by brightrain.aerifal.cx with local (Exim 3.15 #2) id 1j1ySb-0004um-00; Wed, 12 Feb 2020 20:18:13 +0000 Date: Wed, 12 Feb 2020 15:18:13 -0500 From: Rich Felker To: Florian Weimer Cc: Al Viro , "Darrick J. Wong" , Christoph Hellwig , linux-xfs@vger.kernel.org, libc-alpha@sourceware.org, linux-fsdevel@vger.kernel.org Subject: Re: XFS reports lchmod failure, but changes file system contents Message-ID: <20200212201813.GB1663@brightrain.aerifal.cx> References: <874kvwowke.fsf@mid.deneb.enyo.de> <20200212161604.GP6870@magnolia> <20200212181128.GA31394@infradead.org> <20200212183718.GQ6870@magnolia> <87d0ajmxc3.fsf@mid.deneb.enyo.de> <20200212195118.GN23230@ZenIV.linux.org.uk> <87wo8rlgml.fsf@mid.deneb.enyo.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87wo8rlgml.fsf@mid.deneb.enyo.de> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, Feb 12, 2020 at 09:01:22PM +0100, Florian Weimer wrote: > * Al Viro: > > > On Wed, Feb 12, 2020 at 08:15:08PM +0100, Florian Weimer wrote: > > > >> | Further, I've found some inconsistent behavior with ext4: chmod on the > >> | magic symlink fails with EOPNOTSUPP as in Florian's test, but fchmod > >> | on the O_PATH fd succeeds and changes the symlink mode. This is with > >> | 5.4. Cany anyone else confirm this? Is it a problem? > >> > >> It looks broken to me because fchmod (as an inode-changing operation) > >> is not supposed to work on O_PATH descriptors. > > > > Why? O_PATH does have an associated inode just fine; where does > > that "not supposed to" come from? > > It fails on most file systems right now. I thought that was expected. > Other system calls (fsetxattr IIRC) do not work on O_PATH descriptors, > either. I assumed that an O_PATH descriptor was not intending to > confer that capability. Even openat fails. > > Although fchmod does succeed on read-only descriptors, which is a bit > strange. That's intentional and as-specified (and matches all historical practice): "The fchmod() function shall be equivalent to chmod() except that the file whose permissions are changed is specified by the file descriptor fildes." And chmod is specified as: "The application shall ensure that the effective user ID of the process matches the owner of the file or the process has appropriate privileges in order to do this." No alternate behavior regarding permissions is specified; ability to operate on the file does not depend on the open file mode. Rich