linux-kernel - Re: [PATCH 1/2] proc.5: Document /proc/[pid]/setgroups

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Date:	Wed, 11 Feb 2015 09:01:57 +0100
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Michael Kerrisk <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 1/2] proc.5: Document /proc/[pid]/setgroups

Hi Eric,

Ping!

Cheers,

Michael



On 2 February 2015 at 16:36, Michael Kerrisk (man-pages)
<mtk.manpages@...il.com> wrote:
> [Adding Josh to CC in case he has anything to add.]
>
> On 12/12/2014 10:54 PM, Eric W. Biederman wrote:
>>
>> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
>> ---
>>  man5/proc.5 | 15 +++++++++++++++
>>  1 file changed, 15 insertions(+)
>>
>> diff --git a/man5/proc.5 b/man5/proc.5
>> index 96077d0dd195..d661e8cfeac9 100644
>> --- a/man5/proc.5
>> +++ b/man5/proc.5
>> @@ -1097,6 +1097,21 @@ are not available if the main thread has already terminated
>>  .\"       Added in 2.6.9
>>  .\"       CONFIG_SCHEDSTATS
>>  .TP
>> +.IR /proc/[pid]/setgroups " (since Linux 3.19-rc1)"
>> +This file reports
>> +.BR allow
>> +if the setgroups system call is allowed in the current user namespace.
>> +This file reports
>> +.BR deny
>> +if the setgroups system call is not allowed in the current user namespace.
>> +This file may be written to with values of
>> +.BR allow
>> +and
>> +.BR deny
>> +before
>> +.IR /proc/[pid]/gid_map
>> +is written to (enabling setgroups) in a user namespace.
>> +.TP
>>  .IR /proc/[pid]/smaps " (since Linux 2.6.14)"
>>  This file shows memory consumption for each of the process's mappings.
>>  (The
>
> Hi Eric,
>
> Thanks for this patch. I applied it, and then tried to work in
> quite a few other details gleaned from the source code and commit
> message, and Jon Corbet's article at http://lwn.net/Articles/626665/.
> Could you please let me know if the following is correct:
>
>     /proc/[pid]/setgroups (since Linux 3.19)
>            This file displays the string "allow"  if  processes  in
>            the  user  namespace  that  contains the process pid are
>            permitted to employ the setgroups(2)  system  call,  and
>            "deny"  if  setgroups(2)  is  not permitted in that user
>            namespace.
>
>            A privileged process (one with the  CAP_SYS_ADMIN  capa‐
>            bility in the namespace) may write either of the strings
>            "allow" or "deny" to this file before writing a group ID
>            mapping   for   this   user   namespace   to   the  file
>            /proc/[pid]/gid_map.  Writing the string "deny" prevents
>            any  process  in  the user namespace from employing set‐
>            groups(2).
>
>            The default value of  this  file  in  the  initial  user
>            namespace is "allow".
>
>            Once  /proc/[pid]/gid_map has been written to (which has
>            the effect of enabling setgroups(2) in the  user  names‐
>            pace),  it is no longer possible to deny setgroups(2) by
>            writing to /proc/[pid]/setgroups.
>
>            A child user namespace inherits the  /proc/[pid]/gid_map
>            setting from its parent.
>
>            If  the  setgroups  file  has the value "deny", then the
>            setgroups(2) system call can't subsequently be reenabled
>            (by writing "allow" to the file) in this user namespace.
>            This restriction also propagates down to all child  user
>            namespaces of this user namespace.
>
> Thanks,
>
> Michael
>
> --
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/



-- 
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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