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

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Date:	Fri, 25 Apr 2014 21:25:43 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.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

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.

Oleg.

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