linux-kernel - Re: [PATCH 2/2] user_namespaces.7: Update the documention to reflect the fixes for negative groups

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Message-ID: <54F70FE1.60906@gmail.com>
Date:	Wed, 04 Mar 2015 15:00:01 +0100
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Alban Crequy <alban.crequy@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	mtk.manpages@...il.com,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Josh Triplett <josh@...htriplett.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Linux API <linux-api@...r.kernel.org>,
	linux-man <linux-man@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	LSM <linux-security-module@...r.kernel.org>,
	Casey Schaufler <casey@...aufler-ca.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Richard Weinberger <richard@....at>,
	Kenton Varda <kenton@...dstorm.io>,
	stable <stable@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH 2/2] user_namespaces.7: Update the documention to reflect
 the fixes for negative groups

On 02/02/2015 10:31 PM, Alban Crequy wrote:
> Hello,
> 
> Thanks for updating the man page.
> 
> On 12 December 2014 at 22:54, Eric W. Biederman <ebiederm@...ssion.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

Thanks, Alban. I've added code to the example to handle /proc/PID/setgroups
(and tested).

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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