Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755643AbaDKVwb (ORCPT ); Fri, 11 Apr 2014 17:52:31 -0400 Received: from static.92.5.9.176.clients.your-server.de ([176.9.5.92]:54673 "EHLO hallynmail2" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754438AbaDKVwa (ORCPT ); Fri, 11 Apr 2014 17:52:30 -0400 Date: Fri, 11 Apr 2014 23:52:28 +0200 From: "Serge E. Hallyn" To: Andy Lutomirski Cc: "Serge E. Hallyn" , Serge Hallyn , "Eric W. Biederman" , Sean Pajot , lxc-devel@lists.linuxcontainers.org, "linux-kernel@vger.kernel.org" Subject: Re: [lxc-devel] Kernel bug? Setuid apps and user namespaces Message-ID: <20140411215228.GA27354@mail.hallyn.com> References: <874n89rsoc.fsf@xmission.com> <20140402172049.GA13240@sergelap> <20140402173248.GA22804@mail.hallyn.com> <533EF65E.6050508@mit.edu> <20140404183022.GA6728@sergelap> <20140404191000.GA13496@sergelap> <20140407181331.GA15012@mail.hallyn.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Quoting Andy Lutomirski (luto@amacapital.net): > On Mon, Apr 7, 2014 at 11:13 AM, Serge E. Hallyn wrote: > > Quoting Andy Lutomirski (luto@amacapital.net): > >> I'm starting to think that we need to extend dumpable to something > >> much more general like a list of struct creds that someone needs to be > >> able to ptrace, *in addition to current creds* in order to access > >> sensitive /proc files, coredumps, etc. If you get started as setuid, > > > > Hm, yeah, this sort of makes sense. > > > >> then you start with two struct creds in the list (or maybe just your > >> euid and uid). If you get started !setuid, then your initial creds > >> are in the list. It's possible that few or no things will need to > >> change that list after execve. > >> > >> If all of the entries and current->cred are in the same user_ns, then > >> we can dump as userns root. If they're in different usernses, then we > >> dump as global root or maybe the common ancestor root. > >> setuid(getuid()) and other such nastiness may have to empty the list, > >> or maybe we can just use a prctl for that. > > > > A few questions, > > > > 1. is there any other action which would trigger adding a new cred to > > the ist? > > I don't think so. Anyone who can ptrace you from the start can > corrupt you such that you leak rights even if some future action > prevents new ptracers from attaching. > > OTOH, it might be nice for something like an HTTPS server to be able > to fork and shove its private key into the child, while preventing > anyone from ptracing the child. But doing this securely without help > from someone with a different uid might be impossible anyway. > > > > > 2. would execve clear (and re-init) the list of creds? > > Probably. Thoughts? Yeah it seems to me it should be re-initialized, with a cred added to the list for every open fd. > We could have a way to ask execve not to reinit the list. Such a > mechanism would have to require no_new_privs to prevent a > straightforward attack on any setuid binary. If we don't add a cred for every open fd, then I think we need this. If we do, then I'm not sure this makes sense. > We's also want PR_SET_DUMPABLE or a new prctl to be able reset the > list to contain just current-.cred, I think. Yeah PR_SET_DUMPABLE should reset it, agreed. -serge -- 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/