Re: [PATCH 0/2 v2] userns: show current values of user namespace counters

[Eric W. Biederman]

Andrei Vagin <avagin@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
>> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
>> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
>> Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>
>> 
>> 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