Re: [PATCH 03/10] virtio: console: clean up port data immediately at time of unplug

[Amit Shah <amit.shah@redhat.com>]

On (Fri) 19 Jul 2013 [13:11:54], Jason Wang wrote:
> On 07/19/2013 01:02 PM, Amit Shah wrote:
> > On (Fri) 19 Jul 2013 [11:21:47], Jason Wang wrote:
> >> On 07/19/2013 04:16 AM, Amit Shah wrote:
> >
> >>> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> >>> index b04ec95..6bf0df3 100644
> >>> --- a/drivers/char/virtio_console.c
> >>> +++ b/drivers/char/virtio_console.c
> >>> @@ -1501,14 +1501,6 @@ static void remove_port(struct kref *kref)
> >>>  
> >>>  	port = container_of(kref, struct port, kref);
> >>>  
> >>> -	sysfs_remove_group(&port->dev->kobj, &port_attribute_group);
> >>> -	device_destroy(pdrvdata.class, port->dev->devt);
> >>> -	cdev_del(port->cdev);
> >>> -
> >>> -	kfree(port->name);
> >>> -
> >>> -	debugfs_remove(port->debugfs_file);
> >>> -
> >>>  	kfree(port);
> >>>  }
> >>>  
> >>> @@ -1566,6 +1558,14 @@ static void unplug_port(struct port *port)
> >>>  	 */
> >>>  	port->portdev = NULL;
> >>>  
> >>> +	sysfs_remove_group(&port->dev->kobj, &port_attribute_group);
> >>> +	device_destroy(pdrvdata.class, port->dev->devt);
> >>> +	cdev_del(port->cdev);
> >>> +
> >>> +	kfree(port->name);
> >>> +
> >>> +	debugfs_remove(port->debugfs_file);
> >>> +
> >>>  	/*
> >>>  	 * Locks around here are not necessary - a port can't be
> >>>  	 * opened after we removed the port struct from ports_list
> >> Should we remove debugfs file before kfree()? Otherwise looks like a
> >> use-after-free if user access debugfs after kfree().
> > It is removed before kfree() -- kfree() is called in remove_port(),
> > which is called when all the references are dropped.  (Did you confuse
> > kfree(port->name) with kfree(port)?)
> 
> Nope. Looks like port->name were accessed in debugfs_read()?

Ah, got it.  Since this bug existed before this patch as well, I'll
post an additional patch on top of this.

Thanks!

		Amit