Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755152AbaDPSNz (ORCPT ); Wed, 16 Apr 2014 14:13:55 -0400 Received: from mail-lb0-f181.google.com ([209.85.217.181]:63785 "EHLO mail-lb0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753810AbaDPSNx (ORCPT ); Wed, 16 Apr 2014 14:13:53 -0400 MIME-Version: 1.0 In-Reply-To: <20140416180642.GG31074@redhat.com> References: <20140416002010.GA5035@redhat.com> <20140416.085743.1614257692560892039.davem@davemloft.net> <1397664837.19767.410.camel@willson.li.ssimo.org> <20140416180642.GG31074@redhat.com> From: Andy Lutomirski Date: Wed, 16 Apr 2014 11:13:31 -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 11:06 AM, Vivek Goyal wrote: > On Wed, Apr 16, 2014 at 09:31:25AM -0700, Andy Lutomirski wrote: > I am not sure how same issue with happen with cgroups. In the case of > socket example, you are forcing a setuid program to write to standard > output and that setuid program will run in same cgroup as caller and > will have same cgroup as caller. So even if somebody was using cgroup > information for authentication, atleast in this particular case it > will not be a problem. Both unpriviliged and priviliged programs has > same cgroups. > I'm not sure that there's an actual attackable program. But I also see no reason to be convinced that there isn't one, and the problem can easily be avoided by requiring programs to explicitly ask to send their cgroup. >> >> > >> > The only one that *may* be reasonable is the "secret" cgroup name one, >> > however nobody seem to come up with a reason why it is legitimate to >> > allow to keep cgroup names secret. >> > >> > And if you can come up with such a good reason the SO_NOPASSCGROUP >> > option seem the right solution. >> > >> >> This ABI is especially tricky because programs will use it even if >> >> they don't explicitly try to. So just adding the ABI may break >> >> existing assumptions that are relevant to security or correctness. >> > >> > It's not clear to me what you mean by this, either you explicitly use >> > SO_PASSCGROUP or not, it's not like you can involuntarily add a flag ... >> > >> >> The issue here is that the receiver sets SO_(PASS|PEER)CGROUP, forcing >> the sender to identify or authenticate itself. The sender might not >> want to identify itself. Even if you don't buy any secrecy arguments, >> the sender might not intend to authenticate. Certainly no existing >> callers of connect or write intend to authenticate using their cgroup, >> since current kernels don't have those semantics. > > Ok, so passing cgroup information is not necessarily a problem as long > as it is not used for authentication. So say somebody is just logging > all the client request and which cgroup client was in, that should not > be a problem. Do you consider correct attribution of logging messages to be important? If so, then this is a kind of authentication, albeit one where the impact of screwing it up is a bit lower. > > I agree that before somebody uses cgroup information for authentication > purposes, may be there needs to be a bigger debate whether this info > can be used safely for authentication purposes or not and in what > circumstances it is safe to use for authentication. I thought that the original intended user of these patches was SSSD. I have no idea what SSSD wanted them for, but I think it may better. > > But that does not mean that API to pass the cgroup information around is > wrong. > It may not be wrong, but it might be extremely difficult or impossible to use it safely. I think that's something to avoid. --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/