Re: [PACTH v3 1/3] mm, proc: Implement /proc/<pid>/totmaps

[Jann Horn]

On Tue, Aug 16, 2016 at 02:34:15PM -0400, Robert Foss wrote:
> On 2016-08-16 02:18 PM, Jann Horn wrote:
> >On Tue, Aug 16, 2016 at 01:34:14PM -0400, robert.foss@xxxxxxxxxxxxx wrote:
> >>+	}
> >>+
> >>+	return 0;
> >>+
> >>+error:
> >>+	return ret;
> >>+}
> >>+
> >[...]
> >>+const struct file_operations proc_totmaps_operations = {
> >>+	.open		= totmaps_open,
> >>+	.read		= seq_read,
> >>+	.llseek		= seq_lseek,
> >>+	.release	= proc_map_release,
> >>+};
> >
> >As I said regarding v2 already:
> >This won't release priv->task, causing a memory leak (exploitable
> >through a reference counter overflow of the task_struct usage
> >counter).
> 
> Sorry about dropping the ball on that one, what's correct way to release
> priv->task?

get_proc_task() does get_pid_task(), which does get_task_struct(), which
increments the ->usage field of the task. You want the inverse
operation - something that decrements ->usage and checks for zero. This is
done via put_task_struct(), which is defined a few lines below
get_task_struct().

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