Return-Path: Received: from fieldses.org ([173.255.197.46]:58544 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751984AbbIQRaw (ORCPT ); Thu, 17 Sep 2015 13:30:52 -0400 Date: Thu, 17 Sep 2015 13:30:51 -0400 From: "J. Bruce Fields" To: Andreas =?utf-8?Q?Gr=C3=BCnbacher?= Cc: Andreas Gruenbacher , Linux Kernel Mailing List , Linux FS-devel Mailing List , Linux NFS Mailing List , Linux API Mailing List , linux-cifs@vger.kernel.org, LSM List Subject: Re: [RFC v7 10/41] richacl: Permission check algorithm Message-ID: <20150917173051.GC13048@fieldses.org> References: <1441448856-13478-1-git-send-email-agruenba@redhat.com> <1441448856-13478-11-git-send-email-agruenba@redhat.com> <20150911211617.GF11677@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: Sender: linux-nfs-owner@vger.kernel.org List-ID: On Sat, Sep 12, 2015 at 12:12:16AM +0200, Andreas Grünbacher wrote: > 2015-09-11 23:16 GMT+02:00 J. Bruce Fields : > > On Sat, Sep 05, 2015 at 12:27:05PM +0200, Andreas Gruenbacher wrote: > >> + /* > >> + * Apply the group file mask to entries other than owner@ and > >> + * everyone@ or user entries matching the owner. This ensures > >> + * that we grant the same permissions as the acl computed by > >> + * richacl_apply_masks(). > >> + * > >> + * Without this restriction, the following richacl would grant > >> + * rw access to processes which are both the owner and in the > >> + * owning group, but not to other users in the owning group, > >> + * which could not be represented without masks: > >> + * > >> + * owner:rw::mask > >> + * group@:rw::allow > >> + */ > >> + if ((acl->a_flags & RICHACL_MASKED) && richace_is_allow(ace)) > >> + ace_mask &= acl->a_group_mask; > > > > I'm having trouble understanding this. I think the problem is that I > > don't really understand the notation in your example. Is a_group_mask > > zero in that example? I think it must be, in which case, OK I think I > > get it. > > Yes. I'm not sure if the example becomes easier to understand when the > empty group mask and perhaps also the other mask is included. I think it would have been for me. In general I find it confusing to present the mask bits as additional ACEs--they're really pretty different. > > (Though I still have to think about it a little more to convince myself > > that richacl_apply_masks() always gets the same result.) > > I have tried to break the algorithm into digestible pieces. Do you see > another way to make things easier to understand? I just haven't reread those carefully enough yet, working on it.... --b.