Re: Kernel panic at Ubuntu: IMA + Apparmor

Dmitry Kasatkin
2014-04-25T20:52:24Z

On 25 April 2014 23:45, Eric W. Biederman <ebiederm@xmission.com> wrote:
> Dmitry Kasatkin <dmitry.kasatkin@gmail.com> writes:
>
>> On 25 April 2014 23:01, Oleg Nesterov <oleg@redhat.com> wrote:
>>> On 04/25, Eric W. Biederman wrote:
>>>>
>>>> Oleg Nesterov <oleg@redhat.com> writes:
>>>>
>>>> > Well. I _think_ that __fput() and ima_file_free() in particular should not
>>>> > depend on current and/or current->nsproxy. If nothing else, fput() can be
>>>> > called by the unrelated task which looks into /proc/pid/.
>>>> >
>>>> > But again, task_work_add() has more and more users, and it seems that even
>>>> > __fput() paths can do "everything", so perhaps it would be safer to allow
>>>> > to use ->nsproxy in task_work_run.
>>>>
>>>> Like I said, give me a clear motivating case.
>>>
>>> I agree, we need a reason. Currently I do not see one.
>>>
>>>> Right now not allowing
>>>> nsproxy is turning up bugs in __fput. Which seems like a good thing.
>>>
>>> This is what I certainly agree with ;)
>>>
>>
>> Hi,
>>
>> IMA uses kernel_read API which does not know anything about caller.
>> And of course security frameworks are at guard as usual.
>>
>> Exactly after reading first Eric's respons, I thought why to scratch
>> the head when task work queues are indeed designed for tasks...
>
> __fput has no guarantee of running in the task that close the file
> descriptor. If your code depends on that your code is broken.
>
>> And if you to dig for the history, IMA-appraisal was stuck due to
>> lockdep reporting even though it was on non-everlaping cases.
>> IIRC files vs. directories...
>>
>> After that IIRC Al Viro discussed about delayed fput and IIRC Oleg
>> (sorry if I am wrong) introduced task work queues.
>>
>> So IMA-appraisal was able to be upstreamed... That was ~3.4 time frame, IIRC
>>
>> Name space also dated around ~3.4??
>> Apparmor namespace change was also around that time.
>>
>> 3.10 introduces this name space order change and broke IMA-appraisal.
>
> IMA-appraisal is fundamentally broken because I can take a mandatory
> file lock and prevent IMA-apprasial.
>

What file lock are you talking about?
IMA-appraisal does not depends on file locks...

> Using kernel_read is what allows this.
>
>> Isn't it a clear motivating case???
>
> kernel_read is not appropriate for IMA use. The rest of this is just
> the messenger.
>
> IMA needs to use a cousin of kernel_read that operates at a lower level
> than vfs_read. A function that all of the permission checks and the
> fsnotify work.
>
> I am sorry to be the bearer of bad news. But kernel_read is totally
> inappropriate for IMA.
>

So you break IMA-appraisal and declare that it cannot be used now?

> Eric
>

--
Thanks,
Dmitry