> The correct way to fix that remaining problem is probably to make
> sure the array of group IDs is sorted, and contains no duplicates,
> each time it is changed.

Is that really safe, is the list order not used by anything?  (Well,
aside from the primary gid being special, but presumably the primary
gid would be exempt from the sorting, and possibly the de-duping,
anyway.)

Access checking doesn't care about order, I think.  But is there, for
example, code that depends on getgroups() returning a list identical to
the one passed to setgroups()?

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