Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756425AbaDPS7u (ORCPT ); Wed, 16 Apr 2014 14:59:50 -0400 Received: from mail-lb0-f181.google.com ([209.85.217.181]:61833 "EHLO mail-lb0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756296AbaDPS7q (ORCPT ); Wed, 16 Apr 2014 14:59:46 -0400 MIME-Version: 1.0 In-Reply-To: <20140416185153.GI31074@redhat.com> References: <20140416002010.GA5035@redhat.com> <20140416.085743.1614257692560892039.davem@davemloft.net> <1397664837.19767.410.camel@willson.li.ssimo.org> <1397667766.19767.440.camel@willson.li.ssimo.org> <20140416183614.GH31074@redhat.com> <20140416185153.GI31074@redhat.com> From: Andy Lutomirski Date: Wed, 16 Apr 2014 11:59:24 -0700 Message-ID: Subject: Re: [PATCH 2/2] net: Implement SO_PASSCGROUP to enable passing cgroup path To: Vivek Goyal Cc: Simo Sorce , David Miller , Tejun Heo , Daniel Walsh , "linux-kernel@vger.kernel.org" , lpoetter@redhat.com, cgroups@vger.kernel.org, kay@redhat.com, Network Development 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, Apr 16, 2014 at 11:51 AM, Vivek Goyal wrote: > On Wed, Apr 16, 2014 at 11:40:44AM -0700, Andy Lutomirski wrote: >> On Wed, Apr 16, 2014 at 11:36 AM, Vivek Goyal wrote: >> > On Wed, Apr 16, 2014 at 10:29:08AM -0700, Andy Lutomirski wrote: >> > >> > [..] >> >> >> Admittedly cgroups aren't currently as important as uid, but if this >> >> >> changes, then SO_PASSCGROUP, as currently written, will have *exactly* >> >> >> the same problem. >> >> > >> >> > Which is easy to foil by using SO_PEERCGROUP and find out who originally >> >> > opened the socket, which is why that is also available! >> >> >> >> Then please remove SO_PASSCGROUP. >> > >> > SO_PASSCGROUP is important because SO_PEERCGROUP does not work with unix >> > datagram sockets. >> >> Right. I forgot about that. >> >> > >> > Again going back to logging example, if some clients are logging to unix >> > datagram sockets, SO_PASSCGROUP is the only option to figure out cgroup >> > of client. >> >> Hmm. I think that, in your patch, the cgroup that is sent is the >> cgroup of the caller of write/send/sendmsg. What if you changed it to >> use the same cgroup that SO_PEERCRED would use? Would that still >> work? > > No. SO_PEERCRED stores the cgroup information once at the time of > connect(). After that it never changes. > > What if sender changes the cgroup. That information will not be captured. > Also what if multiple client use the same socket fd to writer to logger? > In that case too storing cgroup info in socket will not help. What is the use case of SO_PEERCRED, then? Why can't clients that change cgroup reopen the socket? They're already cgroup-aware. As far as I know, there is probably exactly one client that actually changes cgroups and then tries to log without execing first: systemd (or journald as used by systemd). And this is exactly the component that needs to change to use any new socket option, no matter what. >> > How would it work in logging example? Every time logger receives a >> > message, is it supposed to send another message to client to send >> > SCM_CGROUP? That does not sound right. >> >> No -- just have the logger send the cgroup with every message. Yes, >> it seems silly, but it's probably barely more expensive than with the >> code in your patch. > > So receiver gets the cgroup messages even if it might not want to. There > is no way to say "Hey don't send me SCM_CGROUP's messages". The receiver would only get SCM_CGROUP messages if it set SO_PASSCGROUP. > > Now all loggers need to be modifed to always send SCM_CGROUP messages. And > all other more complicated cases might need a different consideration and > clients and servers will need to be modified accordingly. > > I think it is much simpler to allow passing of cgroup information and > once we figure out some concrete cases where passing of that info is > not desirabe, implement SO_NOPASSCGROUP and modify those *selected few > corner cases* to set this flag on sockets. The problem with SO_NOPASSCGROUP is that the programs that would need to set it are probably already written and don't care about cgroups. --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/