Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755421AbbFLX2D (ORCPT ); Fri, 12 Jun 2015 19:28:03 -0400 Received: from mail-lb0-f177.google.com ([209.85.217.177]:33233 "EHLO mail-lb0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754798AbbFLX16 (ORCPT ); Fri, 12 Jun 2015 19:27:58 -0400 MIME-Version: 1.0 In-Reply-To: References: <1433897388-9567-1-git-send-email-tycho.andersen@canonical.com> <20150610163149.GA5092@redhat.com> From: Andy Lutomirski Date: Fri, 12 Jun 2015 16:27:36 -0700 Message-ID: Subject: Re: [PATCH v4] seccomp: add ptrace options for suspend/resume To: Kees Cook 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: 2915 Lines: 68 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. --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/