Re: [Lsf-pc] [LSF/MM ATTEND] Richacls

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Jan 13, 2015 at 06:23:26PM +0100, Andreas Gruenbacher wrote:
> On 01/13/2015 05:48 PM, Jeremy Allison wrote:
> >My understanding of Christoph's objection (although I'm sure
> >he can chime in himself :-) was that he wanted to see POSIX
> >ACLs reworked as a mapping on top of RichACLs, so that ultimately
> >RichACLs would be the only on-disk format of the EA.
> >
> >I think that is doable, as I think any POSIX ACL can be represented
> >as an underlying RichACL, just not the reverse.
> 
> On of the differences is that permissions in POSIX ACLs do
> accumulate, while in NFSv4 and CIFS ACLs, and therefore also
> richacls, they do not. So the two models are really not
> interchangeable, however annoying that may be.
> 
> For example, with the following POSIX ACL, a non-root process in
> group 5001 and 5002 would not be allowed to open f with O_RDWR, only
> with O_RDONLY *or* O_WRONLY.
> 
>   # file: f
>   # owner: root
>   # group: root
>   user::rw-
>   group::rw-
>   group:5001:r--
>   group:5002:-w-
>   mask::rw-
>   other::---
> 
> In all the other ACL models, the process would be allowed to open f
> with O_RDWR.

If we modified the behavior to permit O_RDWR in this case, would that
cause anyone a problem?

> The rationale for this behavior in POSIX ACLs was / is consistency
> with how the traditional POSIX file permission model works --
> determine which of the (three) sets of permissions applies to a
> process, then check only that set.

The "consistency" leads to kind of weird corner case here.

--b.