Re: [PACTH v1] mm, proc: Implement /proc/<pid>/totmaps

[Mateusz Guzik <mguzik@redhat.com>]

On Tue, Aug 09, 2016 at 12:05:43PM -0400, robert.foss@collabora.com wrote:
> From: Sonny Rao <sonnyrao@chromium.org>
> 
> This is based on earlier work by Thiago Goncales. It implements a new
> per process proc file which summarizes the contents of the smaps file
> but doesn't display any addresses.  It gives more detailed information
> than statm like the PSS (proprotional set size).  It differs from the
> original implementation in that it doesn't use the full blown set of
> seq operations, uses a different termination condition, and doesn't
> displayed "Locked" as that was broken on the original implemenation.
> 
> This new proc file provides information faster than parsing the potentially
> huge smaps file.

I have no idea about usefulness of this.

The patch is definitely buggy with respect to how it implements actual
access to mm.

> +static int totmaps_proc_show(struct seq_file *m, void *data)
> +{
> +	struct proc_maps_private *priv = m->private;
> +	struct mm_struct *mm;
> +	struct vm_area_struct *vma;
> +	struct mem_size_stats *mss_sum = priv->mss;
> +
> +	/* reference to priv->task already taken */
> +	/* but need to get the mm here because */
> +	/* task could be in the process of exiting */
> +	mm = get_task_mm(priv->task);
> +	if (!mm || IS_ERR(mm))
> +		return -EINVAL;
> +

That's not how it's done in smaps.

> +static int totmaps_open(struct inode *inode, struct file *file)
> +{
> +	struct proc_maps_private *priv;
> +	int ret = -ENOMEM;
> +	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> +	if (priv) {
> +		priv->mss = kzalloc(sizeof(*priv->mss), GFP_KERNEL);
> +		if (!priv->mss)
> +			return -ENOMEM;

Cases below explicitly kfree(priv). I can't remember whether the close
routine gets called if this one fails. Either way, something is wrong
here.

> +
> +		/* we need to grab references to the task_struct */
> +		/* at open time, because there's a potential information */
> +		/* leak where the totmaps file is opened and held open */
> +		/* while the underlying pid to task mapping changes */
> +		/* underneath it */
> +		priv->task = get_pid_task(proc_pid(inode), PIDTYPE_PID);

This performs no permission checks that I would see. If you take a look
at smaps you will see the user ends up in proc_maps_open which performs
proc_mem_open(inode, PTRACE_MODE_READ) and gets a mm from there.


> +		if (!priv->task) {
> +			kfree(priv->mss);
> +			kfree(priv);
> +			return -ESRCH;
> +		}
> +
> +		ret = single_open(file, totmaps_proc_show, priv);
> +		if (ret) {
> +			put_task_struct(priv->task);
> +			kfree(priv->mss);
> +			kfree(priv);
> +		}
> +	}
> +	return ret;
> +}
> +

-- 
Mateusz Guzik