On Jun 24 21:37, Bill Zissimopoulos wrote: > On 6/24/16, 12:51 PM, "Corinna Vinschen" behalf of corinna-cygwin@cygwin.com> wrote: > >Not yet. We're coming from the other side. We always have *some* SID. > >pwdgrp::fetch_account_from_windows() in uinfo.cc tries to convert the SID > >to a passwd or group entry. If everything fails, the SID is used in this > >passwd/group entry verbatim, but mapped to uid/gid -1. > > I also noticed that there is no uid mapping for nobody. On my OSX box it > is -2. On many other POSIX systems it appears to be the 32-bit or 16-bit > equivalent of -2. In fact it's an entirely arbitrary choice. On Fedora Linux, for instance, there is no "nogroup", but there is: /etc/passwd: nobody:x:99:99:Nobody:/:/sbin/nologin nfsnobody:x:65534:65534:Anonymous NFS User:/var/lib/nfs:/sbin/nologin /etc/group: nobody:x:99: nfsnobody:x:65534: Note the 65534 here. This is -2 *if* the remote system uses 16 bit signed uid/gid values. However, these days uid/gid values are at least 32 bit, so -2 kind of lost its meaning. > For the time being I am mapping unknown SID’s to -1 as per Cygwin. We could kick this around a bit and maybe reserve -2, 99 or 65534 for an arbitrary "nobody" account. But since we're on Windows the SID value is important, not so much the uid/gid values. > >If you want some specific mapping we can arrange that, but it must not > >be the NULL SID. If you know you're communicating with a Cygwin process, > >what about using an arbitrary, unused SID like S-1-0-42? > > I am inclined to try S-1-5-7 (Anonymous). But I do not know if that is a > bad choice for some reason or other. I thought about Anonymous myself when I wrote my reply to your OP. I refrained from mentioning it because it might have some unexpected side effect we're not aware about. > The main reason that I am weary of using an unused SID is that Microsoft > may decide to assign some special powers to it in a future release (e.g. > GodMode SID). But I agree that this is rather unlikely in the S-1-0-X > namespace. I think it's very unlikely. We could chose any RID value we like and the chance for collision is nil. When I created the new implementation for POSIX ACLs, I toyed around with this already and used a special Cygwin SID within the NULL SID AUTHORITY. I'm not entirely sure why I changed this to the NULL SID deny ACE. I think I disliked the fact that almost every Cygwin ACL would contain a mysterious "unknown SID". On second thought, maybe that would have avoided the UoW problem?!? Well, how should I have known about UoW when I implemanted this, right? > >How do you differ nobody from nogroup if you use the same SID for both, > >btw.? > > I use the same SID for both nobody and nogroup. This should work as long > as you use the permission mapping from the [PERMS] document. Keep in mind that Interix only supported standard POSIX permission bits. Cygwin strives to support POSIX ACLs per POSIX 1003.1e draft 17. That's a bit more extensive. Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat