Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755458AbbFLX3F (ORCPT ); Fri, 12 Jun 2015 19:29:05 -0400 Received: from mail-vn0-f41.google.com ([209.85.216.41]:35776 "EHLO mail-vn0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753746AbbFLX3B (ORCPT ); Fri, 12 Jun 2015 19:29:01 -0400 MIME-Version: 1.0 In-Reply-To: References: <1433897388-9567-1-git-send-email-tycho.andersen@canonical.com> <20150610163149.GA5092@redhat.com> Date: Fri, 12 Jun 2015 16:29:00 -0700 X-Google-Sender-Auth: YWTD9WBY5yI5Enl0PnMnVqbqBWo Message-ID: Subject: Re: [PATCH v4] seccomp: add ptrace options for suspend/resume From: Kees Cook To: Andy Lutomirski Cc: Oleg Nesterov , Tycho Andersen , "linux-kernel@vger.kernel.org" , Linux API , Will Drewry , Roland McGrath , Pavel Emelyanov , "Serge E. Hallyn" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3140 Lines: 75 On Fri, Jun 12, 2015 at 4:27 PM, Andy Lutomirski wrote: > On Wed, Jun 10, 2015 at 1:18 PM, Kees Cook wrote: >> On Wed, Jun 10, 2015 at 10:20 AM, Andy Lutomirski wrote: >>> On Wed, Jun 10, 2015 at 9:31 AM, Oleg Nesterov wrote: >>>> On 06/09, Andy Lutomirski wrote: >>>>> >>>>> On Tue, Jun 9, 2015 at 5:49 PM, Tycho Andersen >>>>> > >>>>> > @@ -556,6 +556,15 @@ static int ptrace_setoptions(struct task_struct *child, unsigned long data) >>>>> > if (data & ~(unsigned long)PTRACE_O_MASK) >>>>> > return -EINVAL; >>>>> > >>>>> > + if (unlikely(data & PTRACE_O_SUSPEND_SECCOMP)) { >>>> >>>> Well, we should do this if >>>> >>>> (data & O_SUSPEND) && !(flags & O_SUSPEND) >>>> >>>> or at least if >>>> >>>> (data ^ flags) & O_SUSPEND >>>> >>>> >>>>> > + if (!config_enabled(CONFIG_CHECKPOINT_RESTORE) || >>>>> > + !config_enabled(CONFIG_SECCOMP)) >>>>> > + return -EINVAL; >>>>> > + >>>>> > + if (!capable(CAP_SYS_ADMIN)) >>>>> > + return -EPERM; >>>>> >>>>> I tend to think that we should also require that current not be using >>>>> seccomp. Otherwise, in principle, there's a seccomp bypass for >>>>> privileged-but-seccomped programs. >>>> >>>> Andy, I simply can't understand why do we need any security check at all. >>>> >>>> OK, yes, in theory we can have a seccomped CAP_SYS_ADMIN process, seccomp >>>> doesn't filter ptrace, you hack that process and force it to attach to >>>> another CAP_SYS_ADMIN/seccomped process, etc, etc... Looks too paranoid >>>> to me. >>> >>> I've sometimes considered having privileged processes I write fork and >>> seccomp their child. Of course, if you're allowing ptrace through >>> your seccomp filter, you open a giant can of worms, but I think we >>> should take the more paranoid approach to start and relax it later as >>> needed. After all, for the intended use of this patch, stuff will >>> break regardless of what we do if the ptracer is itself seccomped. >>> >>> I could be convinced that if the ptracer is outside seccomp then we >>> shouldn't need the CAP_SYS_ADMIN check. That would at least make this >>> work in a user namespace. >> >> But not if that namespace is running under a manager that has added a >> seccomp filter to do things like drop finit_module, as lxc does. > > In that case, criu isn't going to handle seccomp right regardless of > what our security check is, so I think we can safely deal with the > security aspects of that case once we figure out the functionality > part. > > IOW, I think I still like the direct "you must not be seccomped in > order to suspend seccomp" rule. Adding that restriction would be fine by me. -Kees -- Kees Cook Chrome OS Security -- 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/