linux-kernel - Re: [PATCH 1/3] kthread: implement probe_kthread

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 30 Mar 2013 18:00:23 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jens Axboe <axboe@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, david@...morbit.com,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] kthread: implement probe_kthread_data()

Hi Tejun,

On 03/30, Tejun Heo wrote:
>
> On Sat, Mar 30, 2013 at 7:36 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> > > +void *probe_kthread_data(struct task_struct *task)
> > > +{
> > > +     struct kthread *kthread = to_kthread(task);
> > > +     void *data = NULL;
> > > +
> > > +     probe_kernel_read(&data, &kthread->data, sizeof(data));
> > > +     return data;
> > > +}
> >
> > OK, but we can simply check ->vfork_done != NULL ?
>
> Hmm... what if ->vfork_done is pointing to some weird place?

Aah...  "weird place" is not possible if we know that @task is kthread,
it is either NULL or it points into tsk->stack which can only go away
along with task. Note that kthread_stop() already relies on this.

But I guess I missed the fact that this helper should be safe even this
@task can be the a vfork'ed user-space process, yes?

In this case, yes, ->vfork_done can point to task->parent->stack, not
good...

Perhaps,

	voif *kthread_data_safe(struct task_struct *task)
	{
		if (task->parent == kthreadd_task) {
			struct kthread *kthread = to_live_kthread(task);
			if (kthread)
				return kthread->data;
		}

		return NULL;
	}

?

Or we can add to_live_kthread_safe() which checks "parent == kthreadd_task"
instead.

Oleg.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/