Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760708AbXH3Omo (ORCPT ); Thu, 30 Aug 2007 10:42:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757486AbXH3Omf (ORCPT ); Thu, 30 Aug 2007 10:42:35 -0400 Received: from sovereign.computergmbh.de ([85.214.69.204]:45269 "EHLO sovereign.computergmbh.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751330AbXH3Ome (ORCPT ); Thu, 30 Aug 2007 10:42:34 -0400 Date: Thu, 30 Aug 2007 16:42:33 +0200 (CEST) From: Jan Engelhardt To: Trond Myklebust cc: Linux Kernel Mailing List Subject: Re: NFS4 authentification / fsuid In-Reply-To: <1188484337.6755.41.camel@heimdal.trondhjem.org> Message-ID: References: <1188484155.6755.38.camel@heimdal.trondhjem.org> <1188484337.6755.41.camel@heimdal.trondhjem.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1719 Lines: 38 On Aug 30 2007 10:29, Trond Myklebust wrote: >On Thu, 2007-08-30 at 16:12 +0200, Jan Engelhardt wrote: >> >> with NFS3, there is this 'root hole', i.e. any person who has a root >> account (perhaps by use of a laptop) can mount an export (let's say this >> export had the "root_squash" option), and still have a look at the user >> files, because he can locally setuid() into another user. >> >> So I was looking for alternatives. CIFS is my favorite candidate, but it >> has a few issues right now. So does sshfs and about everything I have >> come across. Since I remember NFS4 can use KRB5 authentification, my >> question is, will the NFS(4) server process run with an fsuid equal to >> the user that authenticated? > >NFSv3 should work fine with krb5 too, but that won't solve your problem >with setuid: kerberos saves the TGT in a file on /tmp, so root can still >suid and grab your cred (and the same goes for CIFS). Hm? I do not see this problem with CIFS. The user may have local root, but on the server, he only has his non-root account on the server, and as such, can only operate on the server using this non-root fsuid. Did I miss something? (Especially the /dev/mem thing is not quite clear to me.) >BTW: even when this task is done, a creative root can still find ways to >subvert the security (he can read /dev/mem, replace the kernel with a >compromised one, ....). The bottom line is that if you can't trust root, >don't even log in. Jan -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/