Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752241AbaDQQs5 (ORCPT ); Thu, 17 Apr 2014 12:48:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46361 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751136AbaDQQst (ORCPT ); Thu, 17 Apr 2014 12:48:49 -0400 Subject: Re: [PATCH 2/2] net: Implement SO_PASSCGROUP to enable passing cgroup path From: Simo Sorce To: Andy Lutomirski Cc: Daniel J Walsh , Vivek Goyal , 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: <20140416002010.GA5035@redhat.com> <20140416.085743.1614257692560892039.davem@davemloft.net> <1397664837.19767.410.camel@willson.li.ssimo.org> <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> Content-Type: text/plain; charset="UTF-8" Date: Thu, 17 Apr 2014 12:48:43 -0400 Message-ID: <1397753323.2628.60.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 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. > Here's a real world example from my industry. Suppose I used journald > for logging on a production trading system. The ability to write a > log line that says "I just bought 100000 EUR/USD for > such-and-such-price" attributed to a trading program is absolutely a > security-sensitive operation and must be subject to access control. Eh well if SCM_CREDNTIALS passed the euid you'd se a different user in the logs from the one that is supposed to be writing the log ... but that send the real uid instead oups ... but I think the point is moot for logs, given the previous explanation. > If Common Criteria doesn't say that audit logs need to be resistant to > spoofing, then that's just one more reason that Common Criteria is > broken. IT does say a lot about audit logs, but journald is not classified as an audit log under CC, and I am not sure it can ever be. > I don't use journald for trading logs, and I'd be absolutely daft to > use ordinary syslog, because ordinary syslog doesn't even pretend to > be secure. Right. > But if you're going to design something that claims to be > secure, "well, I can't see how this issue would be exploited" is not > good enough. Did anyone claim the journal is secure to the level you claim it should be. Regardless, systemd can be that secure if it uses also SO_PEERCGROUP in the vulnerable case (when you have a connected socket). Simo. * I think this is the case that matters for journald -- 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/