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Date: Mon, 2 Feb 2015 22:31:08 +0100
Message-ID: <CAMXgnP7phuYTko6fHnxjJTi=HRdoa32uH6dp8DyD9uWPWr2kAg@mail.gmail.com>
Subject: Re: [PATCH 2/2] user_namespaces.7: Update the documention to reflect
 the fixes for negative groups
From: Alban Crequy <alban.crequy@gmail.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Michael Kerrisk-manpages <mtk.manpages@gmail.com>,
        Linux Containers <containers@lists.linux-foundation.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Linux API <linux-api@vger.kernel.org>,
        linux-man <linux-man@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        LSM <linux-security-module@vger.kernel.org>,
        Casey Schaufler <casey@schaufler-ca.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Richard Weinberger <richard@nod.at>,
        Kenton Varda <kenton@sandstorm.io>, stable <stable@vger.kernel.org>,
        Andy Lutomirski <luto@amacapital.net>
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Hello,

Thanks for updating the man page.

On 12 December 2014 at 22:54, Eric W. Biederman <ebiederm@xmission.com> wrote:
(...)
> Furthermore to preserve in some form the useful applications that have
> been setting gid_map without privilege the file /proc/[pid]/setgroups
> was added to allow disabling setgroups.  With the setgroups system
> call permanently disabled in a user namespace it again becomes safe to
> allow writes to gid_map without privilege.
>
> Here is my meager attempt to update user_namespaces.7 to reflect these
> issues.

The program userns_child_exec.c in user_namespaces.7 should be updated
to write in /proc/.../setgroups, near the line:
/* Update the UID and GID maps in the child */

Otherwise, the example given in the manpage does not work:
$ ./userns_child_exec -p -m -U -M '0 1000 1' -G '0 1000 1' bash

Cheers,
Alban
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