Re: [PATCH] groups: don't return unmapped gids in getgroups(2)

From: Andy Lutomirski
Date: Fri Feb 17 2017 - 12:09:33 EST

On Fri, Feb 17, 2017 at 12:44 AM, Aleksa Sarai <asarai@xxxxxxx> wrote:
>>> One thing overlooked by commit 9cc46516ddf4 ("userns: Add a knob to
>>> disable setgroups on a per user namespace basis") is that because
>>> setgroups(2) no longer works in user namespaces it doesn't make any
>>> sense to be returning weird group IDs that the process cannot do
>>> anything with.

> bool DropPrivileges()
> {
> /* ... */
> // Verify that the user isn't still in any supplementary groups

But the user *is* still in a supplementary group. Your proposed
change would break the intent of this code.