Fix missing setgroups() call.

[ximon18]

See: https://github.com/rpm-software-management/rpmlint/blob/fb00ae4bea5905491a8b1ca0e14e38f97cebe8ea/rpmlint/descriptions/BinariesCheck.toml#L120

[partim]

I’m wondering if the correct behaviour is to call setgroups(&[]) (i.e., drop all supplementary groups) if either user or group are provided. The Linux manpage seems to suggest that this is for the supplementary groups only, i.e., you don’t need to include the effective group ID in the list.

Also, setgroups isn’t POSIX, the nix source suggest that it isn’t available e.g. on Apple targets, so this needs to be gated somehow.

[partim]

Ah, great. On FreeBSD, the first item in the array is the effective group ID. So I guess your approach is correct after all. But then what do you do when we only set the user ID? Leave the list alone?

[ximon18]

I actually just did what is listed here in the example: https://docs.rs/nix/latest/nix/unistd/fn.setgroups.html#examples

[ximon18]

Obsoleted by PR #11.