Re: Setuid programs

[Christopher Lemmer Webber <cwebber@dustycloud.org>]

Gábor Boskovits writes:

> Hello,
>
> Christopher Lemmer Webber <cwebber@dustycloud.org> ezt írta (időpont:
> 2020. szept. 9., Sze, 21:00):
>>
>> Maxim Cournoyer writes:
>>
>> > Hello Gabor!
>> >
>> > Gábor Boskovits <boskovits@gmail.com> writes:
>> >
>> >> Hello guix,
>> >>
>> >> I would like to propose an extension to how setuid programs are
>> >> currently handled. The last time I checked it could only do setuid and
>> >> setgid root. Some services, such as postfix need a more fine grained
>> >> setuid setup. I would propose a record type, such as:
>> >> (setuid
>> >> (program setuid-program)
>> >> (setuid setuid-setuid)
>> >> (setgid setuid-setgid)
>> >> (user setuid-user)
>> >> (group setuid-group))
>> >>
>> >> So that there is more fine grained control.
>> >>
>> >> I would also propose to move this to the services framework, so that
>> >> services could extend this field on demand.
>> >>
>> >> Wdyt?
>> >
>> > This sounds great!  I also encountered such limitation and tried to
>> > fixing it in https://issues.guix.info/41763, with some success (and an
>> > unresolved limitation pointed by Chriistopher) but I agree that using a
>> > record makes more sense and is more future proof.
>> >
>> > Maxim
>>
>> I'm eager to use Postfix on Guix (maybe it's me, but I just can't make
>> sense of the weird DSL that opensmtpd uses) so I guess if that's what's
>> necessary it already makes it a good idea.
>>
>> However I don't fully understand the syntax of what you proposed.  Let's
>> see if I can guess with a fake entry
>>
>> #~(setuid
>>    ;; The program to run, from the shady package
>>    (program (string-append #$shady "/bin/scaryfoo")
>>    ;; Would this be a boolean?  If so should it be `setuid?`
> yes, this should be a bool, studi? looks good to me.
>>    (setuid setuid-setuid)
>>    ;; Likewise?
>>    (setgid setuid-setgid)
> yes, the same thing applies here.
>>    ;; Presumably the use we want to set this to
>>    (user setuid-user)
> yes, this should just be the uid of the owner
>>    ;; Presumably the group we want to se this to
> this should be the gid.
>>    (group setuid-group))
>>
>> ... right?
>>
>> I guess this could be done in a backwards compatible way;
>> %setuid-programs could either evaluate to strings or records, so the
>> "simpler" version can remain an option?
> Yes, it can be done this way. Actually I had a bit more general
> solution in mind,
> I feel there should be service to install a file from a store to a
> given place, and with all the access control available,
> like acl-s, if supported. And then provide the whole setuid thing as a
> backwards compatibility layer, somehow like you described.
> For now I guess creating this record type and implementing the
> extended setuid functionality would be a good first step.

A service seems like a really good idea to me in that it feels the most
composable with how Guix currently approaches things.