On Thu, Mar 12, 2015 at 11:54:10AM +1030, Rusty Russell wrote:
> "Michael S. Tsirkin" <mst@xxxxxxxxxx> writes:
> > On device hot-unplug, 9p/virtio currently will kfree channel while
> > it might still be in use.
> >
> > Of course, it might stay used forever, so it's an extremely ugly hack,
> > but it seems better than use-after-free that we have now.
> >
> > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
>
> I'll apply it, but it looks like a bandaid.
Absolutely.
> The right answer would seem to be:
> 1) Use reference counting: 1 for client, 1 for transport.
> 2) When hot unplug, complete (ie. fail) all outstanding requests.
> 3) From then on, fail all incoming requests.
> 4) When refcount hits 0, free the structure.
>
> Thanks,
> Rusty.
Right. Will try to do for 4.1.
>
>
> > ---
> > net/9p/trans_virtio.c | 25 +++++++++++++++++++++----
> > 1 file changed, 21 insertions(+), 4 deletions(-)
> >
> > diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
> > index d8e376a..d1b2f306 100644
> > --- a/net/9p/trans_virtio.c
> > +++ b/net/9p/trans_virtio.c
> > @@ -658,14 +658,31 @@ p9_virtio_create(struct p9_client *client, const char *devname, char *args)
> > static void p9_virtio_remove(struct virtio_device *vdev)
> > {
> > struct virtio_chan *chan = vdev->priv;
> > -
> > - if (chan->inuse)
> > - p9_virtio_close(chan->client);
> > - vdev->config->del_vqs(vdev);
> > + unsigned long warning_time;
> > + bool inuse;
> >
> > mutex_lock(&virtio_9p_lock);
> > +
> > + /* Remove self from list so we don't get new users. */
> > list_del(&chan->chan_list);
> > + warning_time = jiffies;
> > +
> > + /* Wait for existing users to close. */
> > + while (chan->inuse) {
> > + mutex_unlock(&virtio_9p_lock);
> > + msleep(250);
> > + if (time_after(jiffies, warning_time + 10 * HZ)) {
> > + dev_emerg(&vdev->dev, "p9_virtio_remove: "
> > + "waiting for device in use.\n");
> > + warning_time = jiffies;
> > + }
> > + mutex_lock(&virtio_9p_lock);
> > + }
> > +
> > mutex_unlock(&virtio_9p_lock);
> > +
> > + vdev->config->del_vqs(vdev);
> > +
> > sysfs_remove_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);
> > kobject_uevent(&(vdev->dev.kobj), KOBJ_CHANGE);
> > kfree(chan->tag);
> > --
> > MST
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