Re: [PATCH] s390: cio: fix two use-after-free bugs in device.c

[Qinglang Miao]

在 2020/11/20 15:55, Cornelia Huck 写道:
> On Fri, 20 Nov 2020 15:48:49 +0800
> Qinglang Miao <miaoqinglang@xxxxxxxxxx> wrote:
>
> > put_device calls release function which do kfree() inside.
> > So following use of sch&cdev would cause use-after-free bugs.
> >
> > Fix these by simply adjusting the position of put_device.
> >
> > Fixes: 37db8985b211 ("s390/cio: add basic protected virtualization support")
> > Fixes: 74bd0d859dc3 ("s390/cio: fix unlocked access of online member")
> > Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
> > Signed-off-by: Qinglang Miao <miaoqinglang@xxxxxxxxxx>
> > ---
> >   drivers/s390/cio/device.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/s390/cio/device.c b/drivers/s390/cio/device.c
> > index b29fe8d50..69492417b 100644
> > --- a/drivers/s390/cio/device.c
> > +++ b/drivers/s390/cio/device.c
> > @@ -1664,10 +1664,10 @@ void __init ccw_device_destroy_console(struct ccw_device *cdev)
> >   	struct io_subchannel_private *io_priv = to_io_private(sch);
> >   
> >   	set_io_private(sch, NULL);
> > -	put_device(&sch->dev);
> > -	put_device(&cdev->dev);
> >   	dma_free_coherent(&sch->dev, sizeof(*io_priv->dma_area),
> >   			  io_priv->dma_area, io_priv->dma_area_dma);
> > +	put_device(&sch->dev);
> > +	put_device(&cdev->dev);
>
> That change looks reasonable.
>
> >   	kfree(io_priv);
> >   }
> >   
> > @@ -1774,8 +1774,8 @@ static int ccw_device_remove(struct device *dev)
> >   				      ret, cdev->private->dev_id.ssid,
> >   				      cdev->private->dev_id.devno);
> >   		/* Give up reference obtained in ccw_device_set_online(). */
> > -		put_device(&cdev->dev);
> >   		spin_lock_irq(cdev->ccwlock);
> > +		put_device(&cdev->dev);
>
> As the comment above states, the put_device() gives up the reference
> obtained in ccw_device_set_online(). There's at least one more
> reference remaining (held by the caller of the remove function). Moving
> the put_device() does not fix anything here.
Hi, Cornelia

Sorry for the delayed reply.

Your suggestion is reasonable, there is a mistake in this patch for I 
didn't notice that there would be at least one more reference remaining.

So I sent a new patch only to move put_device after dma_free_coherent. I 
put the link as below:
https://lore.kernel.org/lkml/20201201063150.82128-1-miaoqinglang@xxxxxxxxxx/

Thanks!
> >   	}
> >   	ccw_device_set_timeout(cdev, 0);
> >   	cdev->drv = NULL;
>
> .