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

From: Oleg Nesterov <oleg@redhat.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Chris Wright <chrisw@sous-sol.org>,
	Roland McGrath <roland@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 3/3a] ptrace: add _ptrace_may_access()
Date: Thu, 7 May 2009 01:53:49 +0200	[thread overview]
Message-ID: <20090506235349.GC3756@redhat.com> (raw)
In-Reply-To: <20090506080050.GF17457@elte.hu>

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.