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SubjectRe: [RFC] cgroups: implement device whitelist lsm (v2)
Serge E. Hallyn wrote:
> Quoting Pavel Emelyanov (
>> Serge E. Hallyn wrote:
>>> Quoting James Morris (
>>>> On Thu, 13 Mar 2008, Serge E. Hallyn wrote:
>>>>> Quoting James Morris (
>>>>>> On Thu, 13 Mar 2008, Serge E. Hallyn wrote:
>>>>>>> True, but while this change simplifies the code a bit, the semantics
>>>>>>> seem more muddled - devcg will be enforcing when CONFIG_CGROUP_DEV=y
>>>>>>> and:
>>>>>>> SECURITY=n or
>>>>>>> rootplug is enabled
>>>>>>> capabilities is enabled
>>>>>>> smack is enabled
>>>>>>> selinux+capabilities is enabled
>>>>>> Well, this is how real systems are going to be deployed.
>>>>> Sorry, do you mean with capabilities?
>>>> Yes.
>>>> All Fedora, RHEL, CentOS etc. ship with SELinux+capabilities. I can't
>>>> imagine not enabling them on other kernels.
>>>>>> It becomes confusing, IMHO, if you have to change which secondary LSM you
>>>>>> stack with SELinux to enable a cgroup feature.
>>>>> So you're saying selinux without capabilities should still be able to
>>>>> use dev_cgroup? (Just making sure I understand right)
>>>> Nope, SELinux always stacks with capabilities, so havng the cgroup hooks
>>>> in capabilities makes sense (rather than having us change the secondary
>>>> stacking LSM just to enable a feature).
>>> Oh, ok.
>>> Will let the patch stand until Pavel and Greg comment then.
>> Well, I saw your previous patch, that was implemented as just another
>> LSM module and I liked it except for the LSM dependency.
> James and Stephen agree with your LSM qualms. I suppose we could add


> cgroups next to the lsm hooks. I suspect Paul Menage would complain
> about that (Paul?), and I do think it's silly as they are security
> questions, not group tracking questions, but if it's what people want
> I can send out a new patch next week.

The way I see this is: cgroups provide a common way to group tasks
and an API for general configuration - that's the controller "face",
and it's up to the controller to decide where he turns his "back",
IOW where the hooks are placed. For the memory controller - they are
injected directly into the mm code. For this controller, I think it
would be OK to use LSM or about-LSM hooks.

>> Since this version can happily work w/o LSM, I like it too :)
> In an earlier version I asked whether you had any experience with usual
> # rules per container. Do you have an idea? Right now the whitelist is
> a straight list we search through linearly. If # rules is generally
> tiny then I'm inclined to keep it that way...

The # of rules usually has a linear dependency on the number of containers
(each of then has to have an access to /dev/null,zero,random at least), so
having 100 containers we will have to scan through a 300-entries list. I'd
vote for a hash table or a radix/binary/rb tree for that. Or any other way
for non-linear search you can provide :)

> thanks,
> -serge

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