From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Shilovsky Subject: Re: [PATCH v2 0/8] Add O_DENY* support for VFS and CIFS/NFS Date: Tue, 5 Feb 2013 15:33:21 +0400 Message-ID: References: <1358441537-8672-1-git-send-email-piastry@etersoft.ru> <20130130221118.GB15584@fieldses.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-cifs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, wine-devel-5vRYHf7vrtgdnm+yROfE0A@public.gmane.org To: "J. Bruce Fields" Return-path: In-Reply-To: <20130130221118.GB15584-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org> Sender: linux-cifs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: 2013/1/31 J. Bruce Fields : > On Thu, Jan 17, 2013 at 08:52:09PM +0400, 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. > > Maybe that's good enough. A mount flag might be simpler and give > consistent enforcement for all users. > >> >> 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. > > It would be useful to have some really careful documentation of how > these are meant to work. Maybe try updating the open man page? Yes, that's a good idea. Do you mean smth like this? O_DENYMAND - used to inforce a mandatory share reservation scheme of the file access. If this flag is passed, the open fails with -ETXTBSY in following cases: 1) if O_DENYREAD flag is specified and there is another open with O_DENYMAND flag and READ access to the file; 2) if O_DENYWRITE flag is specified and there is another open with O_DENYMAND flag and WRITE access to the file; 3) if READ access is requested and there is another open with O_DENYMAND and O_DENYREAD flags; 4) if WRITE access is requested and there is another open with O_DENYMAND and O_DENYWRITE flags; Also, if O_DENYDELETE flag is specified and the open succeded, any further unlink operation will fail with -ETXTBSY untill this open is closed. Now this flag is processed by CIFS filesystems only. -- Best regards, Pavel Shilovsky. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754886Ab3BELd1 (ORCPT ); Tue, 5 Feb 2013 06:33:27 -0500 Received: from mail-ia0-f172.google.com ([209.85.210.172]:34204 "EHLO mail-ia0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751146Ab3BELdW convert rfc822-to-8bit (ORCPT ); Tue, 5 Feb 2013 06:33:22 -0500 MIME-Version: 1.0 In-Reply-To: <20130130221118.GB15584@fieldses.org> References: <1358441537-8672-1-git-send-email-piastry@etersoft.ru> <20130130221118.GB15584@fieldses.org> Date: Tue, 5 Feb 2013 15:33:21 +0400 X-Google-Sender-Auth: e6urHKY9mpNJLTidji_vgtyPeH8 Message-ID: Subject: Re: [PATCH v2 0/8] Add O_DENY* support for VFS and CIFS/NFS From: Pavel Shilovsky To: "J. Bruce Fields" Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org, wine-devel@winehq.org Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2013/1/31 J. Bruce Fields : > On Thu, Jan 17, 2013 at 08:52:09PM +0400, 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. > > Maybe that's good enough. A mount flag might be simpler and give > consistent enforcement for all users. > >> >> 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. > > It would be useful to have some really careful documentation of how > these are meant to work. Maybe try updating the open man page? Yes, that's a good idea. Do you mean smth like this? O_DENYMAND - used to inforce a mandatory share reservation scheme of the file access. If this flag is passed, the open fails with -ETXTBSY in following cases: 1) if O_DENYREAD flag is specified and there is another open with O_DENYMAND flag and READ access to the file; 2) if O_DENYWRITE flag is specified and there is another open with O_DENYMAND flag and WRITE access to the file; 3) if READ access is requested and there is another open with O_DENYMAND and O_DENYREAD flags; 4) if WRITE access is requested and there is another open with O_DENYMAND and O_DENYWRITE flags; Also, if O_DENYDELETE flag is specified and the open succeded, any further unlink operation will fail with -ETXTBSY untill this open is closed. Now this flag is processed by CIFS filesystems only. -- Best regards, Pavel Shilovsky.