Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757304AbYFCMCF (ORCPT ); Tue, 3 Jun 2008 08:02:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757433AbYFCMBs (ORCPT ); Tue, 3 Jun 2008 08:01:48 -0400 Received: from mail2.shareable.org ([80.68.89.115]:52269 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756122AbYFCMBq (ORCPT ); Tue, 3 Jun 2008 08:01:46 -0400 X-Greylist: delayed 1873 seconds by postgrey-1.27 at vger.kernel.org; Tue, 03 Jun 2008 08:01:45 EDT Date: Tue, 3 Jun 2008 13:01:35 +0100 From: Jamie Lokier To: Al Viro Cc: Michael Kerrisk , Miklos Szeredi , drepper@redhat.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-man@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] utimensat() non-conformances and fixes [v3] Message-ID: <20080603120135.GA28905@shareable.org> References: <482D4665.4050401@gmail.com> <48401E7E.9090304@gmail.com> <20080603112221.GW28946@ZenIV.linux.org.uk> <20080603113018.GA27955@shareable.org> <20080603114921.GX28946@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080603114921.GX28946@ZenIV.linux.org.uk> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1615 Lines: 38 Al Viro wrote: > On Tue, Jun 03, 2008 at 01:39:07PM +0200, Michael Kerrisk wrote: > > > > Is there anything else where the file descriptor's access mode allows > > > doing things on Linux, but the standard requires a permissions check > > > each time? > > > > Jamie, > > > > I can't think of examples offhand -- but I'm also not quite sure what > > your question is about. Could you say a little more? > > "Is anything else equally stupid?", I suspect... AFAICS, behaviour in > question is inherited from futimes(2) in one of the *BSD - nothing to > do about that now (at least 10 years too late). It's rather inconsistent > with a lot of things, starting with "why utimes(2) has weaker requirements > with NULL argument", but we are far too late to fix that. To be fair, having a writable file descriptor only lets you change the mtime to "now", and having a readable file descriptor only lets you change the atime to "now". Changing the times _in general_ can be seen as over-reaching those capabilities and arguably justifies more strict checks. E.g. setting times in the past, you can break some caching systems, Make, etc. Setting times to "now" will not break those things. (A bit analogous with O_APPEND vs. O_WRITE. Someone hands you an O_APPEND descriptor and they can continue to assume you won't clobber earlier records in their file.) -- Jamie -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/