From: ebiederm@xmission.com (Eric W. Biederman)
To: Andrei Vagin <avagin@virtuozzo.com>
Cc: <avagin@openvz.org>, <containers@lists.linux-foundation.org>,
        <linux-kernel@vger.kernel.org>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        Kees Cook <keescook@chromium.org>
References: <1471291822-539-1-git-send-email-avagin@openvz.org>
        <20161006175146.GA25935@outlook.office365.com>
Date: Thu, 06 Oct 2016 14:33:53 -0500
In-Reply-To: <20161006175146.GA25935@outlook.office365.com> (Andrei Vagin's
        message of "Thu, 6 Oct 2016 10:51:47 -0700")
Message-ID: <87wphlclwe.fsf@x220.int.ebiederm.org>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: [PATCH 0/2 v2] userns: show current values of user namespace counters
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2993
Lines: 81

Andrei Vagin <avagin@virtuozzo.com> writes:

> Hello Eric,
>
> What do you think about this series? It should be useful to know current
> usage for user counters.

I am in favor of knowing the values.  Unless there is a good reason not
to we should export the values with a read-only sysctl.  I believe that
is what other similar limits do.

As for having per process knowledge I think that is probably something
we want to solve for these sysctls as well.

I don't think I saw anyone looking at this code from the perspective of
information leaks.  I think we need to ask that question, as similar
interfaces have been problematic from an information leak point of view.

In short I what you are trying to do here is valuable, I just want
to make certain we have a maintainable pattern when we export these.

Eric

>
> Thanks,
> Andrei
>
> On Mon, Aug 15, 2016 at 01:10:20PM -0700, Andrei Vagin wrote:
>> Recently Eric added user namespace counters.  User namespace counters is
>> a feature that allows to limit the number of various kernel objects a
>> user can create. These limits are set via /proc/sys/user/ sysctls on a
>> per user namespace basis and are applicable to all users in that
>> namespace.
>> 
>> User namespace counters are not in the upstream tree yet,
>> you can find them in Eric's tree:
>> https://git.kernel.org/cgit/linux/kernel/git/ebiederm/user-namespace.git/log/?h=for-testing
>> 
>> This patch adds /proc/<pid>/userns_counts files to provide current usage
>> of user namespace counters.
>> 
>>   > cat /proc/813/userns_counts
>>   user_namespaces          101000               1
>>   pid_namespaces           101000               1
>>   ipc_namespaces           101000               4
>>   net_namespaces           101000               2
>>   mnt_namespaces           101000               5
>>   mnt_namespaces           100000               1
>> 
>> The meanings of the columns are as follows, from left to right:
>> 
>>   Name         Object name
>>   UID          User ID
>>   Usage        Current usage
>> 
>> The full documentation is in the second patch.
>> 
>> v2: - describe this file in Documentation/filesystems/proc.txt
>>     - move and rename into /proc/<pid>/userns_counts
>> 
>> Cc: Serge Hallyn <serge.hallyn@canonical.com>
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
>> Signed-off-by: Andrei Vagin <avagin@openvz.org>
>> 
>> Andrei Vagin (1):
>>   kernel: show current values of user namespace counters
>> 
>> Kirill Kolyshkin (1):
>>   Documentation: describe /proc/<pid>/userns_counts
>> 
>>  Documentation/filesystems/proc.txt |  30 +++++++++++
>>  fs/proc/array.c                    |  55 ++++++++++++++++++++
>>  fs/proc/base.c                     |   1 +
>>  fs/proc/internal.h                 |   1 +
>>  include/linux/user_namespace.h     |   8 +++
>>  kernel/ucount.c                    | 102 +++++++++++++++++++++++++++++++++++++
>>  6 files changed, 197 insertions(+)
>> 
>> -- 
>> 2.5.5