[bug#54205] [PATCH v2] Factor out a public FORK-AND-CALL.

[Christine Lemmer-Webber <cwebber@dustycloud.org>]

Liliana Marie Prikler <liliana.prikler@ist.tugraz.at> writes:

> Am Dienstag, dem 01.03.2022 um 13:04 +0000 schrieb Attila Lendvai:
>> > In general, I think such capabilities should be added to exec-
>> > command, rather than resorting to a lambda. It takes a little while
>> > to realize that call-in-fork, fork-and-call or whatever you want to
>> > name it is in fact not pure evil; mainly because shepherd could in
>> > its stead already invoke any lambda you throw at it. That being
>> > said, one should always be aware that this child process runs with
>> > the full permissions of shepherd, which you normally don't want to
>> > do for a service.
>> 
>> 
>> does the above mean that you're concerned about the security
>> implications? if so, then i don't understand, because Guile already
>> allows calling/accessing private functions/symbols, and thus this
>> change doesn't really increase the (already enormous) attack surface
>> in the guile codebase.
> This attack surface is less enormous if you consider the average case
> of a shepherd service in which the arguments to fork+exec-command are
> already evaluated by the time the procedure is call and thus both
> "sane" within and without the fork.  Most of the time people are not
> too conscious about the fact that shepherd can already run arbitrary
> Guile code as part of actions and you typically only use that to its
> fullest extent when you're trying to do something real clever.

In general this would be improved if we move Guix in general, and the
Shepherd services in particular, to an object capability based security
model.

It's on my TODO to lay out a sketch for how this could happen, assuming
there's support for it in the community (which I don't expect to go one
way or another until a plan is laid out to talk about).