From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964984Ab3GLQbB (ORCPT ); Fri, 12 Jul 2013 12:31:01 -0400 Received: from plane.gmane.org ([80.91.229.3]:50084 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933305Ab3GLQbA (ORCPT ); Fri, 12 Jul 2013 12:31:00 -0400 X-Injected-Via-Gmane: http://gmane.org/ To: linux-kernel@vger.kernel.org From: Rasmus Villemoes Subject: Re: [git pull] vfs.git part 2 Date: Fri, 12 Jul 2013 16:30:45 +0000 Organization: D03 Message-ID: <87wqovviyy.fsf@rasmusvillemoes.dk> References: <20130703122918.GK4165@ZenIV.linux.org.uk> <20130712054817.GY4165@ZenIV.linux.org.uk> <8738rk9eai.fsf@rasmusvillemoes.dk> <20130712154833.GA4165@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: 130.225.20.53 User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.3 (gnu/linux) Cancel-Lock: sha1:GDWxxVGgUdCzDdlBpQgLL27WJDI= Cc: linux-fsdevel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Al Viro writes: > On Fri, Jul 12, 2013 at 12:02:45PM +0000, Rasmus Villemoes wrote: > >> But isn't the problem the case where dirname does not exist? I.e., the >> application has to make sure that "/some/where" exists and is a directory >> before open("/some/where", O_CREAT | O_TMPFILE | O_RDWR, 0666) can be >> relied upon to fail on kernels not recognizing O_TMPFILE, instead of >> just creating "where" in "/some". >> >> Just thinking out loud, and please tell me to shut up if it doesn't make >> sense: The documentation for O_DIRECTORY seems to imply that one could >> require O_DIRECTORY to be given when using O_TMPFILE. The "If pathname >> is not a directory, cause the open to fail" certainly seems to make >> sense when O_TMPFILE is used, and older kernels should complain when >> seeing the O_CREAT|O_DIRECTORY combination. It is a hack, though. > > They should, but they won't ;-/ I see; I should test before I post, but... > It's the same problem - we do *not* validate the flags argument. > We'll get to do_last(), hit lookup_open(), which will create the > sucker and go to finish_open_created. Which is past the logics > checking for LOOKUP_DIRECTORY trying to return a non-directory and it > would've been too late to fail anyway - the file has already been > created. IOW, O_DIRECTORY is ignored when O_CREAT is present *and* > file didn't exist already. In that case we almost certainly can treat > that as a bug (i.e. start failing open() on O_CREAT | O_DIRECTORY in > all cases - I'd be _very_ surprised if somebody called open() with > such combination of flags), but that doesn't help with older > kernels... ... it seems that if one then omits O_CREAT, things work out ok, as long as one uses O_RDWR (which is the only sane thing to do with O_TMPFILE, I guess): open("/tmp/test/dir", O_DIRECTORY | O_RDWR, 0666) -> -1; Is a directory open("/tmp/test/dir", O_DIRECTORY | O_RDONLY, 0666) -> 3; Success open("/tmp/test/file", O_DIRECTORY | O_RDWR, 0666) -> -1; Not a directory open("/tmp/test/link_to_file", O_DIRECTORY | O_RDWR, 0666) -> -1; Not a directory open("/tmp/test/link_to_nowhere", O_DIRECTORY | O_RDWR, 0666) -> -1; No such file or directory open("/tmp/test/link_to_dir", O_DIRECTORY | O_RDWR, 0666) -> -1; Is a directory open("/tmp/test/link_to_dir", O_DIRECTORY | O_RDONLY, 0666) -> 3; Success open("/tmp/test/link_to_dir", O_NOFOLLOW | O_DIRECTORY | O_RDWR, 0666) -> -1; Too many levels of symbolic links open("/tmp/test/link_to_dir", O_NOFOLLOW | O_DIRECTORY | O_RDONLY, 0666) -> -1; Too many levels of symbolic links (The above flags are what an old kernel would effectively see with or without O_TMPFILE present, I suppose.) How about simply making O_TMPFILE == O_DIRECTORY | O_RDWR | O_TMPFILE_INTERNAL, and letting the correct use be open("/some/dir", O_TMPFILE) [with or without a mode argument] Using O_DIRECTORY when we don't want to open a directory, and omitting O_CREAT when we do want to create something new, is somewhat counter-intuitive, but I think this would solve the problem with old kernels. Rasmus