bug#72012: [PATCH] id: Warn if user in more groups than `id` can reliably print

[Pádraig Brady]

On 09/07/2024 05:22, Otto Kekäläinen wrote:
> While rare, it is possible for a user to be a member in more groups than
> what the system limit allows (on Linux typically NGROUPS_MAX=65536) and
> if that is the case, running `id` or `id user` will not print all of
> them. This is a minor bug, but easily fixable by emitting a warning if
> it happens.
> ---
>   src/id.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/src/id.c b/src/id.c
> index 38d5517bd..c572b2d99 100644
> --- a/src/id.c
> +++ b/src/id.c
> @@ -401,6 +401,13 @@ print_full_info (char const *username)
>           ok &= false;
>           return;
>         }
> +    else if (sysconf(_SC_NGROUPS_MAX) > 0 && n_groups > 
> sysconf(_SC_NGROUPS_MAX))
> +      {
> +        fprintf (stderr,
> +                 _("Warning: User '%s' may be member of more groups than "\
> +                   "the system allows\n"),
> +                 (username != NULL) ? username : "");
> +      }
>   
>       if (n_groups > 0)
>         fputs (_(" groups="), stdout);

I'm a bit confused with this patch.
If the n_groups is larger than NGROUPS_MAX what consequence will it have?
I.e. is there any point to id(1) warning about this edge case?
id will be able to show all of the n_groups in this case right?
I interpret NGROUPS_MAX as a static limit(ation),
which more dynamic interfaces (like getgrouplist) are not constrained to.

cheers,
Pádraig