linux-kernel - Re: Kernel panic at Ubuntu: IMA + Apparmor

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Date:	Fri, 25 Apr 2014 12:40:32 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Dmitry Kasatkin <d.kasatkin@...sung.com>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	john.johansen@...onical.com, Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	James Morris <jmorris@...ei.org>, viro@...IV.linux.org.uk,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kernel-team@...ts.ubuntu.com
Subject: Re: Kernel panic at Ubuntu: IMA + Apparmor

Oleg Nesterov <oleg@...hat.com> writes:

> On 04/25, Eric W. Biederman wrote:
>>
>> Oleg Nesterov <oleg@...hat.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


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