Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933465AbbFJR3q (ORCPT ); Wed, 10 Jun 2015 13:29:46 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:35459 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750917AbbFJR3h (ORCPT ); Wed, 10 Jun 2015 13:29:37 -0400 Date: Wed, 10 Jun 2015 17:29:31 +0000 From: Serge Hallyn To: Andy Lutomirski Cc: Oleg Nesterov , Tycho Andersen , "linux-kernel@vger.kernel.org" , Linux API , Kees Cook , Will Drewry , Roland McGrath , Pavel Emelyanov Subject: Re: [PATCH v4] seccomp: add ptrace options for suspend/resume Message-ID: <20150610172931.GD4069@ubuntumail> References: <1433897388-9567-1-git-send-email-tycho.andersen@canonical.com> <20150610163149.GA5092@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4111 Lines: 101 Quoting Andy Lutomirski (luto@amacapital.net): > 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 I really do intend to look at your old proposed tree for improving that... have only done a once-over so far, though. > 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. > > >> > @@ -590,6 +590,10 @@ void secure_computing_strict(int this_syscall) > >> > { > >> > int mode = current->seccomp.mode; > >> > > >> > + if (config_enabled(CONFIG_CHECKPOINT_RESTORE) && > >> > + unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) > >> > + return; > >> > + > >> > if (mode == 0) > >> > return; > >> > else if (mode == SECCOMP_MODE_STRICT) > >> > @@ -691,6 +695,10 @@ u32 seccomp_phase1(struct seccomp_data *sd) > >> > int this_syscall = sd ? sd->nr : > >> > syscall_get_nr(current, task_pt_regs(current)); > >> > > >> > + if (config_enabled(CONFIG_CHECKPOINT_RESTORE) && > >> > + unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) > >> > + return SECCOMP_PHASE1_OK; > >> > + > >> > >> If it's not hard, it might still be nice to try to fold this into > >> mode. This code is rather hot. If it would be a mess, then don't > >> worry about it for now. > > > > IMO, this would be a mess ;) At least compared to this simple patch. > > > > Suppose we add SECCOMP_MODE_SUSPENDED. Not only this adds the problems > > with detach if the tracer dies. > > > > We need to change copy_seccomp(). And it is not clear what should we > > do if the child is traced too. > > > > We need to change prctl_set_seccomp() paths. > > > > And even the "tracee->seccomp.mode = SECCOMP_MODE_SUSPENDED" code needs > > some locking even if the tracee is stopped, we need to avoid the races > > with SECCOMP_FILTER_FLAG_TSYNC from other threads. > > > > Agreed. Let's hold off until this becomes a problem (if it ever does). > > --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/