Re: [PATCH 0/5] Networking cgroup controller

[महेश बंडेवार]

On Thu, Aug 25, 2016 at 9:09 AM, Tejun Heo <t...@kernel.org> wrote:
> Hello, Mahesh.
>
> On Thu, Aug 25, 2016 at 08:54:19AM -0700, Mahesh Bandewar (महेश बंडेवार) 
> wrote:
>> In short most of the associated problems are handled by the
>> cgroup-infra / APIs while all that need separate solution in
>> alternatives.  Tejun, feels like I'm advocating cgroup approach to you
>> ;)
>
> My concern here is that the proposed fixed mechanism isn't gonna be
> enough.  Port range matching wouldn't scale, so we'd need some hashmap
> style thing which may be too expensive for simple matches so either we
> do something adaptive or have different interfaces for the two and so
> on.  IOW, I think this approach is likely to replicate what iptables
> have been doing with its extensions.  I don't doubt that it is one of
> the workable approaches but hardly an attractive one especially at
> this point.
>
> ebpf approach does have its shortcomings for sure but mending them
> seems a lot more manageable and future-proof than going with fixed but
> constantly expanding set of operations.  e.g. We can add per-cgroup
> bpf programs which are called only on socket creation or other major
> events, or just let bpf programs which get called on bind(2), and add
> some per-cgroup state variables which are maintained by cgroup code
> which can be used from these bpf programs.
>
Well, I haven't seen any of these yet (please point me the right place
if I missed) Especially the hooks that allows users to add per-cgroup
bpf programs that can be used in control-path (I think Daniel's recent
patches allow in data-path).

> Thanks.
>
> --
> tejun
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Re: [PATCH 0/5] Networking cgroup controller

[महेश बंडेवार]

On Wed, Aug 24, 2016 at 2:03 PM, Tejun Heo  wrote:
> Hello, Anoop.
>
> On Wed, Aug 10, 2016 at 05:53:13PM -0700, Anoop Naravaram wrote:
>> This patchset introduces a cgroup controller for the networking subsystem as 
>> a
>> whole. As of now, this controller will be used for:
>>
>> * Limiting the specific ports that a process in a cgroup is allowed to bind
>>   to or listen on. For example, you can say that all the processes in a
>>   cgroup can only bind to ports 1000-2000, and listen on ports 1000-1100, 
>> which
>>   guarantees that the remaining ports will be available for other processes.
>>
>> * Restricting which DSCP values processes can use with their sockets. For
>>   example, you can say that all the processes in a cgroup can only send
>>   packets with a DSCP tag between 48 and 63 (corresponding to TOS values of
>>   192 to 255).
>>
>> * Limiting the total number of udp ports that can be used by a process in a
>>   cgroup. For example, you can say that all the processes in one cgroup are
>>   allowed to use a total of up to 100 udp ports. Since the total number of 
>> udp
>>   ports that can be used by all processes is limited, this is useful for
>>   rationing out the ports to different process groups.
>>
>> In the future, more networking-related properties may be added to this
>> controller.
>
> Thanks for working on this; however, I share the sentiment expressed
> by others that this looks like too piecemeal an approach.  If there
> are no alternatives, we surely should consider this but it at least
> *looks* like bpf should be able to cover the same functionalities
> without having to revise and extend in-kernel capabilities constantly.
>
My primary concern is the cost that need to be paid to get this functionality.
(a) The suggested alternatives eBPF either can't solve the problem in
the current form or need substantial work to get it done. e.g.
udp-port-limit since there is no notion of "maintaining
counters-per-group-of-processes". This is solved by the cgroup infra.
(b) Also the hooks implemented are mostly with a per packet cost vs.
once when you are establishing the channel. Also not sure if the LSM
approach will allow some privileged user to over-ride the filters
attached and thus override the limits imposed. This is on top of the
administrative costs that currently don't have solution for and you
get it for free with cgroup infra.

In short most of the associated problems are handled by the
cgroup-infra / APIs while all that need separate solution in
alternatives.  Tejun, feels like I'm advocating cgroup approach to you
;)

Thanks,
--mahesh..


> Thanks.
>
> --
> tejun
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Re: [PATCH 0/5] Networking cgroup controller

[महेश बंडेवार]

On Tue, Aug 23, 2016 at 1:49 AM, Parav Pandit  wrote:
> Hi Anoop,
>
> Regardless of usecase, I think this functionality is best handled as
> LSM functionality instead of cgroup.
>
I'm not so sure about that. Cgroup APIs are useful and this is just an
extension to it.


> Tasks which are proposed in this patch are related to access control checks.
> LSM already has required hooks for socket operations such as bind(),
> listen() as few small examples.
>
> Refer to security_socket_listen() which invokes LSM specific hooks.
> This is invoked in source/net/socket.c as part of listen() system call.
> LSM hook callback can check whether a given a process can listen to
> requested UDP port or not.
>
This has administrative overhead that is not addressed. The underlying
cgroup infrastructure takes care of it in this (current)
implementation.

> Parav
>
>
[...]
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