Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751603AbaJOXH6 (ORCPT ); Wed, 15 Oct 2014 19:07:58 -0400 Received: from mail-lb0-f175.google.com ([209.85.217.175]:56636 "EHLO mail-lb0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751130AbaJOXH4 (ORCPT ); Wed, 15 Oct 2014 19:07:56 -0400 MIME-Version: 1.0 In-Reply-To: <20141015225900.GC988@ubuntu-mba51> References: <1413296756-25071-1-git-send-email-seth.forshee@canonical.com> <1413296756-25071-3-git-send-email-seth.forshee@canonical.com> <543E8983.5090001@mit.edu> <20141015150512.GA22951@ubuntu-mba51> <20141015225900.GC988@ubuntu-mba51> From: Andy Lutomirski Date: Wed, 15 Oct 2014 16:07:34 -0700 Message-ID: Subject: Re: [PATCH v4 2/5] fuse: Support fuse filesystems outside of init_user_ns To: Andy Lutomirski , Miklos Szeredi , fuse-devel@lists.sourceforge.net, "linux-kernel@vger.kernel.org" , Linux FS Devel , "Eric W. Biederman" , "Serge H. Hallyn" Cc: Seth Forshee Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 15, 2014 at 3:59 PM, Seth Forshee wrote: > On Wed, Oct 15, 2014 at 10:05:46AM -0700, Andy Lutomirski wrote: >> On Wed, Oct 15, 2014 at 8:05 AM, Seth Forshee >> wrote: >> > On Wed, Oct 15, 2014 at 07:49:39AM -0700, Andy Lutomirski wrote: >> >> On 10/14/2014 07:25 AM, Seth Forshee wrote: >> >> > Update fuse to translate uids and gids to/from the user namspace >> >> > of the process servicing requests on /dev/fuse. Any ids which do >> >> > not map into the namespace will result in errors. inodes will >> >> > also be marked bad when unmappable ids are received from >> >> > userspace. >> >> > >> >> > Due to security concerns the namespace used should be fixed, >> >> > otherwise a user might be able to gain elevated privileges or >> >> > influence processes that the user would otherwise be unable to >> >> > manipulate. Thus the namespace of the mounting process is used >> >> > for all translations, and this namespace is required to be the >> >> > same as the one in use when /dev/fuse was opened. >> >> > >> >> >> >> I'm not sure that this is necessary if my nosuid patch goes in, but I >> >> also don't think it makes any sense to hold this up while we find a >> >> perfect solution. >> >> >> >> Is there a decent way to extend this to different translation schemes in >> >> the future (e.g. a flag at fs setup that could be used)? >> > >> > I think it would be possible to relax the translation scheme >> > restrictions in the future, certainly that's easier than tightening down >> > a looser restriction. I still favor picking one namespace to use for >> > translation (surely that's how it would work with other filesystems >> > anyway) rather than using the current namespace during /dev/fuse I/O. I >> > did an implementation using the latter technique, and it's far more >> > complex with no benefits that I can see. >> >> Long term, I think we'll want more flexible translations for >> filesystems on removable media, even when both the mounter and the >> accessing process are in the init user namespace. But this can wait. > > You've piqued my interest. What are you thinking of which would require > this flexibility? > For an easy example, if I stick a USB stick into my computer and copy a file to it, I probably want the file to be owned by uid 0 in the FS metadata (but still owned by me as reported by stat(2) and friends). For a more complex example, tools like Sandstorm (http://sandstorm.io) probably want to use FUSE mounted by an outer (non-root) userns and accessed from an inner userns. With your patches, this *might* work, but it might also be a little tricky. I can also see this ability being extremely useful for NFS and other network filesystems, where keeping all the uids in sync is currently a royal PITA. --Andy -- 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/