Return-Path: linux-nfs-owner@vger.kernel.org Received: from fn.samba.org ([216.83.154.106]:54567 "EHLO mail.samba.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754911Ab3CETHv (ORCPT ); Tue, 5 Mar 2013 14:07:51 -0500 Message-ID: <51364285.4040406@samba.org> Date: Tue, 05 Mar 2013 14:07:49 -0500 From: Simo MIME-Version: 1.0 To: "J. Bruce Fields" CC: Andy Lutomirski , Pavel Shilovsky , linux-kernel@vger.kernel.org, linux-cifs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, wine-devel@winehq.org Subject: Re: [PATCH v3 0/7] Add O_DENY* support for VFS and CIFS/NFS References: <1362065133-9490-1-git-send-email-piastry@etersoft.ru> <512FD1D5.3010106@mit.edu> <20130304211923.GI20389@fieldses.org> <5135250A.30604@samba.org> <20130305181306.GA15816@fieldses.org> In-Reply-To: <20130305181306.GA15816@fieldses.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Sender: linux-nfs-owner@vger.kernel.org List-ID: On 03/05/2013 01:13 PM, J. Bruce Fields wrote: > On Mon, Mar 04, 2013 at 05:49:46PM -0500, Simo wrote: >> On 03/04/2013 04:19 PM, J. Bruce Fields wrote: >>> On Thu, Feb 28, 2013 at 01:53:25PM -0800, Andy Lutomirski wrote: >>>> [possible resend -- sorry] >>>> >>>> On 02/28/2013 07:25 AM, Pavel Shilovsky wrote: >>>>> This patchset adds support of O_DENY* flags for Linux fs layer. These flags can be used by any application that needs share reservations to organize a file access. VFS already has some sort of this capability - now it's done through flock/LOCK_MAND mechanis, but that approach is non-atomic. This patchset build new capabilities on top of the existing one but doesn't bring any changes into the flock call semantic. >>>>> >>>>> These flags can be used by NFS (built-in-kernel) and CIFS (Samba) servers and Wine applications through VFS (for local filesystems) or CIFS/NFS modules. This will help when e.g. Samba and NFS server share the same directory for Windows and Linux users or Wine applications use Samba/NFS share to access the same data from different clients. >>>>> >>>>> According to the previous discussions the most problematic question is how to prevent situations like DoS attacks where e.g /lib/liba.so file can be open with DENYREAD, or smth like this. That's why one extra flag O_DENYMAND is added. It indicates to underlying layer that an application want to use O_DENY* flags semantic. It allows us not affect native Linux applications (that don't use O_DENYMAND flag) - so, these flags (and the semantic of open syscall that they bring) are used only for those applications that really want it proccessed that way. >>>>> >>>>> So, we have four new flags: >>>>> O_DENYREAD - to prevent other opens with read access, >>>>> O_DENYWRITE - to prevent other opens with write access, >>>>> O_DENYDELETE - to prevent delete operations (this flag is not implemented in VFS and NFS part and only suitable for CIFS module), >>>>> O_DENYMAND - to switch on/off three flags above. >>>> O_DENYMAND doesn't deny anything. Would a name like O_RESPECT_DENY be >>>> better? >>>> >>>> Other than that, this seems like a sensible mechanism. >>> I'm a little more worried: these are mandatory locks, and applications >>> that use them are used to the locks being enforced correctly. Are we >>> sure that an application that opens a file O_DENYWRITE won't crash if it >>> sees the file data change while it holds the open? >> The redirector may simply assume it has full control of that part of >> the file and not read nor send data until the lock is released too, >> so you get conflicting views of the file contents between different >> clients if you let a mandatory lock not be mandatory. >> >>> In general the idea of making a mandatory lock opt-in makes me nervous. >>> I'd prefer something like a mount option, so that we know that everyone >>> on that one filesystem is playing by the same rules, but we can still >>> mount filesystems like / without the option. >> +1 >> >>> But I'll admit I'm definitely not an expert on Windows locking and may >>> be missing something about how these locks are meant to work. >> Mandatory locks really are mandatory in Windows. >> That may not be nice to a Unix system but what can you do ? > I wonder if we could repurpose the existing -omand mount option? > > That would be a problem for anyone that wants to allow mandatory fcntl > locks without allowing share locks. I doubt anyone sane actually uses > mandatory fcntl locks, but still I suppose it would probably be better > to play it safe and use a new mount option. Maybe we should have a -o win_semantics option :-) /me runs Simo.