From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vivek Goyal Subject: Re: [PATCH 2/2] net: Implement SO_PASSCGROUP to enable passing cgroup path Date: Thu, 17 Apr 2014 13:12:56 -0400 Message-ID: <20140417171256.GB25334@redhat.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Simo Sorce , Daniel J Walsh , David Miller , Tejun Heo , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , lpoetter-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kay-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Network Development To: Andy Lutomirski Return-path: Content-Disposition: inline In-Reply-To: Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: netdev.vger.kernel.org On Thu, Apr 17, 2014 at 09:55:08AM -0700, Andy Lutomirski wrote: > On Thu, Apr 17, 2014 at 9:48 AM, Simo Sorce wrote: > > On Thu, 2014-04-17 at 09:37 -0700, Andy Lutomirski wrote: > >> On Thu, Apr 17, 2014 at 9:24 AM, Simo Sorce wrote: > >> > On Thu, 2014-04-17 at 09:11 -0700, Andy Lutomirski wrote: > >> >> > >> >> No. The logging daemon thinks it wants to know who the writer is, but > >> >> the logging daemon is wrong. It actually wants to know who composed a > >> >> log message destined to it. The caller of write(2) may or may not be > >> >> the same entity. > >> > > >> > This works both ways, and doesn't really matter, you are *no* better off > >> > w/o this interface. > >> > > >> >> If this form of SO_PASSCGROUP somehow makes it into a pull request for > >> >> Linus, I will ask him not to pull it and/or to revert it. I think > >> >> he'll agree that write(2) MUST NOT care who called it. > >> > > >> > And write() does not, there is no access control check being performed > >> > here. This call is the same as getting the pid of the process and > >> > crawling /proc with that information, just more efficient and race-free. > >> > >> Doing it using the pid of writer is wrong. So is doing it with the > >> cgroup of the writer. The fact that it's even possible to use the pid > >> of the caller of write(2) is a mistake, but that particular mistake > >> is, unfortunately, well-enshrined in history. > >> > >> > > >> > I repeat, it is *not* access control. > >> > > >> > >> Sure it is. > >> > >> Either correct attribution of logs doesn't matter, in which case it > >> makes little difference how you do it, or it does matter, in which > >> case it should be done right. > > > > Well journald can *also* get SO_PEERCGROUP and log anomalies if the 2 > > differ. That is if the log happens on a connected socket. > > > > If the log happens on a unix datagram* then SO_PEERCGROUP is not > > available because there is no connect(), however write() cannot be used > > either, only sendmsg() AFAIK, so the "setuid" binary attack does not > > apply. > > > > Or you could only send SCM_CGROUP when the writer asks sendmsg to send > it, in which case this whole problem goes away. Sending SCM_CGROUP explicitly is also sending cgroup info at write(2) time and if receiver uses that info for access control, it can be problematic. Thanks Vivek