Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752561Ab1EDQXP (ORCPT ); Wed, 4 May 2011 12:23:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48542 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750802Ab1EDQXO (ORCPT ); Wed, 4 May 2011 12:23:14 -0400 Subject: Re: [PATCH 5/7] seccomp_filter: Document what seccomp_filter is and how it works. From: Eric Paris To: Steven Rostedt Cc: Frederic Weisbecker , Will Drewry , Ingo Molnar , linux-kernel@vger.kernel.org, kees.cook@canonical.com, agl@chromium.org, jmorris@namei.org, Randy Dunlap , Linus Torvalds , Andrew Morton , Tom Zanussi , Arnaldo Carvalho de Melo , Peter Zijlstra , Thomas Gleixner Date: Wed, 04 May 2011 12:22:40 -0400 In-Reply-To: <1304525169.25414.2427.camel@gandalf.stny.rr.com> References: <1303960136-14298-1-git-send-email-wad@chromium.org> <1303960136-14298-4-git-send-email-wad@chromium.org> <20110428070636.GC952@elte.hu> <1304002571.2101.38.camel@localhost.localdomain> <20110429131845.GA1768@nowhere> <20110503012857.GA8399@nowhere> <1304511396.25414.2422.camel@gandalf.stny.rr.com> <1304524465.10692.21.camel@localhost.localdomain> <1304525169.25414.2427.camel@gandalf.stny.rr.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Message-ID: <1304526163.10692.33.camel@localhost.localdomain> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2683 Lines: 83 On Wed, 2011-05-04 at 12:06 -0400, Steven Rostedt wrote: > On Wed, 2011-05-04 at 11:54 -0400, Eric Paris wrote: > > > As this is a deny by default interface which only allows you to further > > restrict you couldn't add more than 1 syscall if you didn't have an > > explict 'apply' action. > > > > SECCOMP_FILTER_SET, __NR_fo, "a=0" > > SECCOMP_FILTER_SET, __NR_read, "1" == EPERM > > > > Maybe apply on set is fine after the first apply, but we definitely need > > some way to do more than 1 set before the rules are applied.... > > So we could have SET be 'or' and APPLY be 'and'. > > SECCOMP_FILTER_SET, __NR_foo, "a=0" > SECCOMP_FILTER_SET, __NR_read, "1" == EPERM When I said "== EPERM" I meant that the given prctl call would return EPERM. I'm going to pretend that you didn't type it. > SECCOPM_FILTER_APPLY > > SECCOMP_FILTER_SET, __NR_foo, "b=0" > SECCOPM_FILTER_APPLY > > Will end up being: > > (foo: a == 0 || read: "1") && (foo: b == 0) > > The second set/apply now removes the read option, and foo only works if > a is 0 and b is 0. > > This would also work for children, as they can only restrict (with > 'and') and can not add more control. I think we pretty much agree although I'm pretty that we will have 1 filter per syscall. So the rules would really be (in your syntax) Rule1: (foo: a == 0 && b == 0) OR Rule2: (read: "1") Although logically the same, it's not just one huge rule. I don't see any need for any operation other than an &&. Before the first "set" you can add new syscalls. After the first set you can only && onto existing syscalls. So the following set of operations: SECCOMP_FILTER_SET, __NR_foo, "a=0" SECCOMP_FILTER_SET, __NR_read, "1" SECCOPM_FILTER_APPLY SECCOMP_FILTER_SET, __NR_foo, "b=0" SECCOMP_FILTER_APPLY SECCOMP_FILTER_SET, __NR_write, "1" SECCOMP_FILTER_APPLY Would return EPERM for the __NR_write entry since it was a new syscall after a set. I think we agree on all this. I do have a question on some syntax proposed a while back. Given: SECCOMP_FILTER_SET, __NR_foo, "a=0" SECCOMP_FILTER_SET, __NR_foo, "b=0" SECCOMP_FILTER_APPLY I would think to keep the interface consistent that should result in foo: (a=0) && (b=0) But I think the proposal was that we should instead have just foo: (b=0) What's the logic behind having a second call overwrite uncommitted changes? I sorta feel like if I put it in there, I must have wanted it in there :) -Eric -- 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/