Re: Position of primary group in in getgrouplist

[yelninei--- via Bug reports for the GNU Hurd]

Sep 10, 2026, 23:03 by samuel.thiba...@gnu.org:

> yelni...@tutamail.com, le jeu. 10 sept. 2026 20:19:09 +0200, a ecrit:
>
>> Sep 10, 2026, 17:49 by samuel.thiba...@gnu.org:
>>
>> > yelni...@tutamail.com, le jeu. 10 sept. 2026 19:31:03 +0200, a ecrit:
>> >
>> >> Sep 10, 2026, 16:45 by samuel.thiba...@gnu.org:
>> >>
>> >> >> Is this a bug in Hurd or in glibc/nscd?
>> >> >> Changing the nscd lookup to insert the group name at the beginning 
>> >> >> instead of the end would fix it
>> >> >>
>> >> >
>> >> > Perhaps we just need to fix glibc's setgroups to make sure that the
>> >> > current effective gid is first in the list given to the auth server,
>> >> > fixing the order if needed.
>> >>
>> >> Fixing setgroups is not enough because i.e. _merge_implied_gids also 
>> >> assumes that the pw_gid is first for setgrouplist and does not use 
>> >> setgroups.
>> >>
>> >
>> > But doesn't it properly cope with keeping the first element first?
>> >
>> Yes it does. It is just that it gets the gid list from getgrouplist which 
>> might or might not have the pw_gid as the first element. Should that add the 
>> primary gid explicitly first and then merge the other gids afterwards?
>>
>
> The primary gid will be first in the list.to be processed by
> idvec_merge_ids, and idvec_merge will leave the first element of
> implied_gids as it is.
>
What if implied_gids is empty such as during login? I think this is what is 
causing my egid to be set to wheel (my first group) instead of my pw_gid after 
login. At least after making sure that the pw_gid gets merged first fixed the 
issue.

To be sure we are talking about the same thing: I mean this 
https://cgit.git.savannah.gnu.org/cgit/hurd/hurd.git/tree/libshouldbeinlibc/idvec-impgids.c#n61
 


>> > The only way that applications have to modify the list without knowing
>> > about the hurd convention is setgroups, as seen from a unix view.  So
>> > that's the only place that needs to take care of the conversion of
>> > convention, and everything below can just keep the hurd convention
>> > correct.
>> >
>> >> Wouldnt it be netter to ensure this in __nscd_getgrouplist to prepend the 
>> >> group instead of appending it and make the normal and nscd output 
>> >> identical?
>> >>
>> >
>> > That will only fix nscd. We want glibc to expose a unix behavior, so we
>> > have to fix it when it happens not to.
>> >
>> Once the list reaches setgroups there is no special gid anymore (apart from 
>> the hurd convention). How is setgroups supposed to know what the extra gid 
>> specified in the call to getgrouplist was and potentially "correct" the list?
>>
>
> It can use getegid().
>

You mean setgroups should prepend the current egid to the request to ensure 
Hurd conventions?

> Samuel
>