Re: [RFC PATCH 3/3a] ptrace: add _ptrace_may_access()

[Oleg Nesterov <oleg@redhat.com>]

On 05/06, Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@redhat.com> wrote:
>
> > +	task_lock(task);
> >  	retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH);
> > +	task_unlock(task);
> >  	if (retval)
> > -		goto bad;
> > +		goto unlock_creds;
>
> Hm, that's a bit ugly - why dont you reuse ptrace_may_access(),
> which does much of this already?

Indeed, even the changelog mentions this.

I was going to cleanup this later. Because I think that
__ptrace_may_access() should die. It has only one caller, mm_for_maps().
I will re-check, but it looks a bit strange. More precisely, I just
can't understand it. Why we can't just do

	struct mm_struct *mm_for_maps(struct task_struct *task)
	{
		struct mm_struct *mm = get_task_mm(task);

		if (mm && mm != current->mm && !ptrace_may_access()) {
			mmput(mm);
			mm = NULL;
		}

		return mm;
	}

? We do not care if this task exits and clears ->mm right before
or after ptrace_may_access(), and this is possible eith the current
code too once it drops tasklist.

Oleg.