Bug#698102: eglibc: initgroups changes egid on kfreebsd

[Petr Salinger <Petr.Salinger@seznam.cz>]

> Unfortuantely, POSIX declined to specify setgroups() and initgroups() is
> not in any standard, so it's hard to say which behavior is right and
> which is wrong.  It seems possible to argue any of the following:
>
> 1. The bug is in kFreeBSD's implementation of setgroups(), which must
>    be fixed so that eglibc's initgroups() implementation works as
>    expected.
>
> 2. The bug is in eglibc's implementation of initgroups(), which must be
>    fixed so that it works properly with kFreeBSD's setgroups().
>
> 3. Since both behaviors of setgroups() and initgroups() are seen "in
>    the wild", programs that depend on the linux kernel behavior are
>    broken and should be fixed as they become known.
>
> Personally I'm leaning towards 3 here, since these are buggy not only on
> debian/kFreeBSD but on real FreeBSD as well.

Even POSIX point out that egid might be somewhere in supplementary groups
http://pubs.opengroup.org/onlinepubs/9699919799/functions/getgroups.html

  The getgroups() function shall fill in the array grouplist with the
  current supplementary group IDs of the calling process. It is
  implementation-defined whether getgroups() also returns the effective
  group ID in the grouplist array.

Under FreeBSD kernel, the "egid" is groups[0], see
http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/kern/kern_prot.c

IMO, there is no bug, the behaviour is implementation-defined.

Petr