Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752475AbaDQRrO (ORCPT ); Thu, 17 Apr 2014 13:47:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:21654 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751125AbaDQRrG (ORCPT ); Thu, 17 Apr 2014 13:47:06 -0400 Subject: Re: [PATCH 2/2] net: Implement SO_PASSCGROUP to enable passing cgroup path From: Simo Sorce To: Andy Lutomirski Cc: Vivek Goyal , Daniel J Walsh , David Miller , Tejun Heo , "linux-kernel@vger.kernel.org" , lpoetter@redhat.com, cgroups@vger.kernel.org, kay@redhat.com, Network Development In-Reply-To: References: <20140416180642.GG31074@redhat.com> <20140416185936.GJ31074@redhat.com> <534FF61B.4010901@redhat.com> <1397750674.2628.44.camel@willson.li.ssimo.org> <1397751853.2628.50.camel@willson.li.ssimo.org> <1397753323.2628.60.camel@willson.li.ssimo.org> <20140417171256.GB25334@redhat.com> <1397756025.2628.64.camel@willson.li.ssimo.org> Content-Type: text/plain; charset="UTF-8" Date: Thu, 17 Apr 2014 13:47:01 -0400 Message-ID: <1397756821.2628.69.camel@willson.li.ssimo.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2014-04-17 at 10:35 -0700, Andy Lutomirski wrote: > On Thu, Apr 17, 2014 at 10:33 AM, Simo Sorce wrote: > > On Thu, 2014-04-17 at 10:26 -0700, Andy Lutomirski wrote: > >> > >> Not really. write(2) can't send SCM_CGROUP. Callers of sendmsg(2) > >> who supply SCM_CGROUP are explicitly indicating that they want their > >> cgroup associated with that message. Callers of write(2) and send(2) > >> are simply indicating that they have some bytes that they want to > >> shove into whatever's at the other end of the fd. > > > > But there is no attack vector that passes by tricking setuid binaries to > > write to pre-opened file descriptors on sendmsg(), and for the other > > cases (connected socket) journald can always cross check with > > SO_PEERCGROUP, so why do we care again ? > > Because the proposed code does not do what I described, at least as > far I as I can tell. You do realize that we have been speaking in hypothetical for a while now ? Even without doing the SO_PEERCRED, you are not going to fool the log, as it gathers a ton of other info about the process, and cgroup is just one of the infos used to classify the log. There are also credentials, pid, and a lot of other things. Even if a setuid binary could be tricked to send a message with an "impostor" cgroup don't you think you'd see other things out of place ? (wrong uid, wrong pid, etc...). What I am telling you is that userspace has all the tools it needs to not get fooled, as long as cgroup information retrieved via SO_PASSCGROUP is not uniquely used to authenticate a peer process for connected sockets. Simo. -- 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/