Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755420AbaJGWTg (ORCPT ); Tue, 7 Oct 2014 18:19:36 -0400 Received: from mail-la0-f50.google.com ([209.85.215.50]:60872 "EHLO mail-la0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752691AbaJGWTe (ORCPT ); Tue, 7 Oct 2014 18:19:34 -0400 MIME-Version: 1.0 In-Reply-To: <87zjd7r1z9.fsf@x220.int.ebiederm.org> References: <1412683977-29543-1-git-send-email-avagin@openvz.org> <20141007133039.GG7996@ZenIV.linux.org.uk> <20141007133339.GH7996@ZenIV.linux.org.uk> <87r3yjy64e.fsf@x220.int.ebiederm.org> <20141007204627.GI28519@ubuntumail> <87wq8bvbzg.fsf@x220.int.ebiederm.org> <20141007213257.GJ28519@ubuntumail> <87zjd7r1z9.fsf@x220.int.ebiederm.org> From: Andy Lutomirski Date: Tue, 7 Oct 2014 15:19:12 -0700 Message-ID: Subject: Re: [PATCH] [RFC] mnt: add ability to clone mntns starting with the current root To: "Eric W. Biederman" Cc: Serge Hallyn , Al Viro , Andrey Vagin , Linux FS Devel , "linux-kernel@vger.kernel.org" , Linux API , Andrey Vagin , Andrew Morton , Cyrill Gorcunov , Pavel Emelyanov , Serge Hallyn , Rob Landley 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 Tue, Oct 7, 2014 at 2:42 PM, Eric W. Biederman wrote: > > I am squinting and looking this way and that but while I can imagine > someone more clever than I can think up some unique property of rootfs > that makes it a little more exploitable than just mounting a ramfs, > but since you have to be root to exploit those properties I think the > game is pretty much lost. Yes. rootfs might not be empty, it might have totally insane permissions, and it's globally shared, which makes it into a wonderful channel to pass things around that shouldn't be passed around. Can non-root do this? You'd need to be in a userns with a "/" that isn't MNT_LOCKED. Can this happen on any normal setup? FWIW, I think we should unconditionally MNT_LOCKED the root on userns unshare, even if it's the only mount. > >>> >> So it is only root (and not root in a container) who can get to the >>> >> exposed rootfs. >>> >> >>> >> I have a vague memory someone actually had a real use in miminal systems >>> >> for being able to get back to the rootfs and being able to use rootfs as >>> >> the rootfs. There was even a patch at that time that Andrew Morton was >>> >> carrying for a time to allow unmounting root and get at rootfs, and to >>> >> prevent the oops on rootfs unmount in some way. >>> >> >>> >> So not only do I not think it is a bug to get back too rootfs, I think >>> >> it is a feature that some people have expressed at least half-way sane >>> >> uses for. >>> > >>> > They can still do that if they want, using chroot :) >>> >>> It would take fchdir or fchroot and a directory file descriptor open on >>> rootfs. Frequently there is no appropriate directory file descriptor. >> >> ? you can always escape if you're simply chrooted. waterbuffalo :) > > filesystem type rootfs. > > Eric > > -- > To unsubscribe from this list: send the line "unsubscribe linux-api" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Andy Lutomirski AMA Capital Management, LLC -- 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/