From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760740Ab3B1Vxb (ORCPT ); Thu, 28 Feb 2013 16:53:31 -0500 Received: from mail-pa0-f49.google.com ([209.85.220.49]:33963 "EHLO mail-pa0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755450Ab3B1Vx2 (ORCPT ); Thu, 28 Feb 2013 16:53:28 -0500 Message-ID: <512FD1D5.3010106@mit.edu> Date: Thu, 28 Feb 2013 13:53:25 -0800 From: Andy Lutomirski User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130219 Thunderbird/17.0.3 MIME-Version: 1.0 To: Pavel Shilovsky CC: 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> In-Reply-To: <1362065133-9490-1-git-send-email-piastry@etersoft.ru> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [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. --Andy