From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2992866AbXDYRUT (ORCPT ); Wed, 25 Apr 2007 13:20:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S2992878AbXDYRUT (ORCPT ); Wed, 25 Apr 2007 13:20:19 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:57892 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2992864AbXDYRUQ (ORCPT ); Wed, 25 Apr 2007 13:20:16 -0400 Date: Wed, 25 Apr 2007 12:20:12 -0500 From: "Serge E. Hallyn" To: "H. Peter Anvin" Cc: Miklos Szeredi , akpm@linux-foundation.org, serue@us.ibm.com, viro@ftp.linux.org.uk, linuxram@us.ibm.com, ebiederm@xmission.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, containers@lists.osdl.org, linux-security-module@vger.kernel.org Subject: Re: [patch] unprivileged mounts update Message-ID: <20070425172012.GA20336@sergelap.austin.ibm.com> References: <462F87EA.1000002@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <462F87EA.1000002@zytor.com> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Quoting H. Peter Anvin (hpa@zytor.com): > Miklos Szeredi wrote: > > > > Andrew, please skip this patch, for now. > > > > Serge found a problem with the fsuid approach: setfsuid(nonzero) will > > remove filesystem related capabilities. So even if root is trying to > > set the "user=UID" flag on a mount, access to the target (and in case > > of bind, the source) is checked with user privileges. > > > > Root should be able to set this flag on any mountpoint, _regardless_ > > of permissions. > > > > Right, if you're using fsuid != 0, you're not running as root Sure, but what I'm not clear on is why, if I've done a prctl(PR_SET_KEEPCAPS, 1) before the setfsuid, I still lose the CAP_FS_MASK perms. I see the special case handling in cap_task_post_setuid(). I'm sure there was a reason for it, but this is a piece of the capability implementation I don't understand right now. I would send in a patch to make it honor current->keep_capabilities, but I have a feeling there was a good reason not to do so in the first place. > (fsuid is > the equivalent to euid for the filesystem.) If it were really the equivalent then I could keep my capabilities :) after changing it. > I fail to see how ruid should have *any* impact on mount(2). That seems > to be a design flaw. May be, but just using fsuid at this point stops me from enabling user mounts under /share if /share is chmod 000 (which it is). thanks, -serge