Re: Kernel panic at Ubuntu: IMA + Apparmor

Eric W. Biederman
2014-04-25T19:41:08Z

Oleg Nesterov <oleg@redhat.com> writes:

> On 04/25, Eric W. Biederman wrote:
>>
>> Oleg Nesterov <oleg@redhat.com> writes:
>>
>> > Eric, this makes me think again that we should do exit_task_namespaces()
>> > after exit_task_work(). We already discussed this before, but this looks
>> > like another indication this change makes sense.
>>
>> I know you mentioned something about that. I haven't actually had much
>> time to think about it.
>>
>> > The problem with fput() from free_nsproxy() was hopefully also fixed by
>> > e7b2c4069252. The main motivation for "move" was "outside of exit_notify".
>> > Even if we fix the paths above task_work_add() can have another user which
>> > wants ->nsproxy.
>> >
>> > What do you think?
>>
>> I am scratching my head. Delayed work that depends on current sort of
>> blows my mind.
>
> But task_work_add(task) was specially introduced to run a callback in the
> task's context.
>
>> That is utter nonsense.
>
> Yes I agree, _perhaps_ we can fix this particular problem without changing
> the exit_namespace/work ordering, and perhaps this makes sense anyway.
>
> 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. Right now not allowing
nsproxy is turning up bugs in __fput. Which seems like a good thing.

Eric