From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot1-f66.google.com ([209.85.210.66]:46533 "EHLO mail-ot1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726167AbeJLGjm (ORCPT ); Fri, 12 Oct 2018 02:39:42 -0400 Received: by mail-ot1-f66.google.com with SMTP id o21so10611478otb.13 for ; Thu, 11 Oct 2018 16:10:13 -0700 (PDT) From: Paul Moore To: Jann Horn CC: , Tycho Andersen , Kees Cook , Linux API , , , Oleg Nesterov , kernel list , "Eric W. Biederman" , , Christian Brauner , Andy Lutomirski , "linux-security-module" , , Stephen Smalley , Eric Paris Date: Thu, 11 Oct 2018 19:10:03 -0400 Message-ID: <1666564e4f8.2781.85c95baa4474aabc7814e68940a78392@paul-moore.com> In-Reply-To: References: <20180927151119.9989-1-tycho@tycho.ws> <20180927151119.9989-4-tycho@tycho.ws> <20181008151629.hkgzzsluevwtuclw@brauner.io> <20181008162147.ubfxxsv2425l2zsp@brauner.io> <20181008181815.pwnqxngj22mhm2vj@brauner.io> <20181009132850.fp6yne2vgmfpi27k@brauner.io> <16662034750.2781.85c95baa4474aabc7814e68940a78392@paul-moore.com> Subject: Re: [PATCH v7 3/6] seccomp: add a way to get a listener fd from ptrace MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On October 11, 2018 9:40:06 AM Jann Horn wrote: > On Thu, Oct 11, 2018 at 9:24 AM Paul Moore wrote: >> On October 10, 2018 11:34:11 AM Jann Horn wrote: >>> On Wed, Oct 10, 2018 at 5:32 PM Paul Moore wrote: >>>> On Tue, Oct 9, 2018 at 9:36 AM Jann Horn wrote: >>>>> +cc selinux people explicitly, since they probably have opinions on t= his >>>> >>>> I just spent about twenty minutes working my way through this thread, >>>> and digging through the containers archive trying to get a good >>>> understanding of what you guys are trying to do, and I'm not quite >>>> sure I understand it all. However, from what I have seen, this >>>> approach looks very ptrace-y to me (I imagine to others as well based >>>> on the comments) and because of this I think ensuring the usual ptrace >>>> access controls are evaluated, including the ptrace LSM hooks, is the >>>> right thing to do. >>> >>> Basically the problem is that this new ptrace() API does something >>> that doesn't just influence the target task, but also every other task >>> that has the same seccomp filter. So the classic ptrace check doesn't >>> work here. >> >> Due to some rather unfortunate events today I'm suddenly without easy ac= cess to the kernel code, but would it be possible to run the LSM ptrace acc= ess control checks against all of the affected tasks? If it is possible, h= ow painful would it be? > > There are currently no backlinks from seccomp filters to the tasks > that use them; the only thing you have is a refcount. If the refcount > is 1, and the target task uses the filter directly (it is the last > installed one), you'd be able to infer that the ptrace target is the > only task with a reference to the filter, and you could just do the > direct check; but if the refcount is >1, you might end up having to > take some spinlock and then iterate over all tasks' filters with that > spinlock held, or something like that. That's what I was afraid of. Unfortunately, I stand by my previous statements that we still probably wan= t a LSM access check similar to what we currently do for ptrace. -- paul moore www.paul-moore.com