From: "J. Bruce Fields" Subject: Re: [NFS] [PATCH] nfs4, special files, and set/listxattr asymmetry Date: Tue, 8 Jan 2008 16:57:37 -0500 Message-ID: <20080108215736.GP22155@fieldses.org> References: <20080108182038.GJ22155@fieldses.org> <200801082147.m08LlF3D023364@agora.fsl.cs.sunysb.edu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Cc: Trond Myklebust , nfs@lists.sourceforge.net To: Erez Zadok Return-path: Received: from neil.brown.name ([220.233.11.133]:53824 "EHLO neil.brown.name" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751480AbYAHV5q (ORCPT ); Tue, 8 Jan 2008 16:57:46 -0500 Received: from brown by neil.brown.name with local (Exim 4.63) (envelope-from ) id 1JCMS8-0000By-Dm for linux-nfs@vger.kernel.org; Wed, 09 Jan 2008 08:57:44 +1100 In-Reply-To: <200801082147.m08LlF3D023364-zop+azHP2WsZjdeEBZXbMidm6ipF23ct@public.gmane.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, Jan 08, 2008 at 04:47:15PM -0500, Erez Zadok wrote: > A few months ago I looked into the issue of xattrs and copyup in more > detail, when I was tracking a problem for a user using an SE-linux enabled > livecd with unionfs. I didn't realize before then that selinux made such a > heavy use of xattrs. After tracking down the code maze I found out that the > list of xattrs being defined/used depends on your overall security mode and > global security ops. > > Anyway, xattrs can be used for security reasons, and really any semantics > could be attached to them. So in Unionfs I take the conservative approach: > if unionfs is compiled with xattr support, then during copyup I try to copy > the xattrs too (if any exist). If unionfs fails to copyup the xattrs, then > I abort the copyup. I figured it's safer to abort the copyup (which is > typically initiated when trying to modify a file on a readonly > branch/media), than to potentially open up a security hole by giving a > copied-up file more permissions than its source file may have had. This > policy has so far worked for unionfs, at least for those users who use > xattrs/selinux, and in my limited testing. But maybe I've got to rethink > it? > > NFS in some sense shares some common traits with a stackable file system, in > that it has three "layers": client -> server -> backing-store f/s. I'm > curious how does nfs/d handle xattrs (and selinux's use of them)? Does the > client depend on having xattr support of any sort? Does the server depend > on having xattr support in the export f/s? How do you handle mixes of those > when one of the three layers has xattr support and another doesn't? We ignore xattr's entirely for now. The labeled nfs people (mailing list at labeled-nfs@linux-nfs.org) have plans to address the selinux case, but I haven't really followed that. --b. ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace _______________________________________________ NFS maillist - NFS@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/nfs _______________________________________________ Please note that nfs@lists.sourceforge.net is being discontinued. Please subscribe to linux-nfs@vger.kernel.org instead. http://vger.kernel.org/vger-lists.html#linux-nfs