Help requested with KAuth backends : OS X

[René J. V. Bertin]

Sune Vuorela wrote:

> I know nothing about mac, and only have a limited knowledge of KAuth, on
> linux, but I'll give it a go replying anyways.

Thanks, that's a start :)

> Whenever an application wants something that requires elevated
> priviledges, it contacts policykit, that does the authorization and
> execution as the relevant user.

Are you sure it always does the actual execution? It comes with pkexec, but dbus 
has a similar tool, and it seems to stand to reason that's the one DBus uses to 
launch privileged helpers...

> Thus, there is no setuid bits in place.

Except on pkexec and dbus-daemon-helper-tool ... I *presume* that the euid!=uid 
aspect you get inside a setuid process isn't inherited by any child that process 
spawns, but I have yet to verify that.

>   2) How is the platform API for invocating things as a different user /
>      with admin priviledges?
>      - then implement a kauth backend on top of that api.

That's the annoying bit: the straightforward API is deprecated, and replaced 
with something involving launchd. I think it'll be much easier and more flexible 
to implement a helper backend that comes with its own setuid proxy.
The Service Management framework that would be the modern alternative is 
cumbersome to deploy, requiring code-signing of all parties involved among other 
niceties.

> I'd say that on a linux system, the kauth bits is mostly relevant to
>  - systemsettings and related KCM's

There might be a selected few KCMs requiring privileges that make sense outside 
of Plasma.

>  - special hardware requiring applications. Maybe KStars interacting
>    with a telescope, or a theoretical KAdvancedSewingMachine, K3DPrinter
>    or similar.

What would they need privileges for that cannot be taken care of by a native 
interface?

An example might be a KF5 frontend to VirtualBox (or simply VirtualBox calling 
upon KAuth). Running a VM with a "raw" (direct access) .vmdk disk image 
currently requires making the disk device file user-writable manually on OS X 
(or running with admin privileges on MS Windows); this could be taken care of 
automatically by the front-end.

R.