Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752044AbaDQS57 (ORCPT ); Thu, 17 Apr 2014 14:57:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52765 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751110AbaDQS5s (ORCPT ); Thu, 17 Apr 2014 14:57:48 -0400 Date: Thu, 17 Apr 2014 14:57:42 -0400 From: Vivek Goyal To: Simo Sorce Cc: Andy Lutomirski , Daniel J Walsh , David Miller , Tejun Heo , "linux-kernel@vger.kernel.org" , lpoetter@redhat.com, cgroups@vger.kernel.org, kay@redhat.com, Network Development Subject: Re: [PATCH 2/2] net: Implement SO_PASSCGROUP to enable passing cgroup path Message-ID: <20140417185742.GB32527@redhat.com> References: <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> <1397759013.2628.86.camel@willson.li.ssimo.org> <20140417185023.GA32527@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140417185023.GA32527@redhat.com> 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 On Thu, Apr 17, 2014 at 02:50:23PM -0400, Vivek Goyal wrote: > On Thu, Apr 17, 2014 at 02:23:33PM -0400, Simo Sorce wrote: > > 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. > > > > Ok let me backtrack, apparently if you explicitly use connect() on a > > datagram socket then you *can* write() (thanks to Vivek for checking > > this). > > > > So you can trick something to write() to it but you can't do > > SO_PEERCGROUP on the other side, because it is not really a connected > > socket, the connection is only faked on the sender side by constructing > > sendmsg() messages with the original address passed into connect(). > > > > So given this unfortunate circumstance, requiring the client to > > explicitly pass cgroup data on unix datagram sockets may be an > > acceptable request IMO. > > > > Perhaps this could be done with a sendmsg() header flag or simplified > > ancillary data even, rather than forcing the sender process to retrieve > > and construct the whole information which is already available in > > kernel. > > So what would be the protocol here? When should somebody send an > SCM_CGROUP message using sendmsg()? I don't know how it will even be used for systemd logging case. systemd provides various ways to connect stdout of services. So say a service's stdout is connected to a connected datagram socket and all printf() messages to stdout are being logged by receiver in journal. Now how would sender know that it is supposed to send SCM_CGROUP? One needs to modify printf() now? Thanks Vivek -- 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/