On Tue, Aug 09, 2016 at 12:05:43PM -0400, robert.f...@collabora.com wrote:
> From: Sonny Rao <sonny...@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
