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

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Date:   Fri, 17 Feb 2017 09:09:06 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Aleksa Sarai <asarai@...e.de>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Aleksa Sarai <cyphar@...har.com>, dev@...ncontainers.org,
        Linux API <linux-api@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH] groups: don't return unmapped gids in getgroups(2)

On Fri, Feb 17, 2017 at 12:44 AM, Aleksa Sarai <asarai@...e.de> 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.