Re: pppd service crash in linux-3.13.6

[Peter Hurley]

[ +cc Eric Biederman ]

On 03/13/2014 01:55 PM, Peter Hurley wrote:
> Hi Oleg,
>
> On 03/13/2014 01:06 PM, Oleg Nesterov wrote:
> > On 03/10, Peter Hurley wrote:
> > > [ +cc Oleg Nesterov ]
> >
> > Thanks.
> >
> > > The NULL ptr dereference is from following the current->nsproxy ptr
> > > in ppp_register_channel().
> > >
> > > This was broken by
> > >
> > > commit 8aac62706adaaf0fab02c4327761561c8bda9448
> > > Author: Oleg Nesterov <oleg@xxxxxxxxxx>
> > > Date:   Fri Jun 14 21:09:49 2013 +0200
> > >
> > >      move exit_task_namespaces() outside of exit_notify()
> > >
> > > which moved the exit_task_namespaces(tsk) before disassociate_ctty().
> >
> > Heh. OK, we can move it down after disassociate_ctty(), the original
> > motivation for that commit was the problem which was also (hopefully)
> > fixed by e7b2c406925273 "fput: task_work_add() can fail if the caller
> > has passed exit_task_work()".

Thanks for fixing that!
tty teardown (hangup from disassociate_ctty) requires fput() to work :)

> I didn't look into what motivated the change; I will now though.
>
> > In fact I think that it makes sense to move it down after
> > exit_task_work() anyway. But this is almost off-topic and I'd like to
> > avoid this right now.
> >
> > OTOH, why we should delay disassociate_ctty? IOW, do you see any
> > potential problem with the trivial patch below?

Won't work.

> I have no idea what kind of dependencies might exist between
> task works, cgroup_exit() and all the teardown that disassociate_ctty()
> does. I'll look into though.

cgroup_exit() can exec a userspace process (the notify_on_exit() facility)
which requires both namespace and tty facilities.
Plus, proc_exit_connector() uses netlink which uses user_ns.

I think it's better to have task namespaces valid up to exit_notify().

Regards,
Peter Hurley
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