Re: [PATCH] usbip: give back URBs for unsent unlink requests during cleanup

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Aug 06, 2021 at 10:10:14PM +0530, Anirudh Rayabharam wrote:
> In vhci_device_unlink_cleanup(), the URBs for unsent unlink requests are
> not given back. This sometimes causes usb_kill_urb to wait indefinitely
> for that urb to be given back. syzbot has reported a hung task issue [1]
> for this.
> 
> To fix this, give back the urbs corresponding to unsent unlink requests
> (unlink_tx list) similar to how urbs corresponding to unanswered unlink
> requests (unlink_rx list) are given back. Since the code is almost the
> same, extract it into a new function and call it for both unlink_rx and
> unlink_tx lists.
> 
> [1]: https://syzkaller.appspot.com/bug?id=08f12df95ae7da69814e64eb5515d5a85ed06b76
> 
> Reported-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com
> Tested-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com
> Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
> ---
>  drivers/usb/usbip/vhci_hcd.c | 47 ++++++++++++++++++++++++++----------
>  1 file changed, 34 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
> index 4ba6bcdaa8e9..45f98aa12895 100644
> --- a/drivers/usb/usbip/vhci_hcd.c
> +++ b/drivers/usb/usbip/vhci_hcd.c
> @@ -945,7 +945,8 @@ static int vhci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
>  	return 0;
>  }
>  
> -static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
> +static void __vhci_cleanup_unlink_list(struct vhci_device *vdev,
> +		struct list_head *unlink_list)
>  {
>  	struct vhci_hcd *vhci_hcd = vdev_to_vhci_hcd(vdev);
>  	struct usb_hcd *hcd = vhci_hcd_to_hcd(vhci_hcd);
> @@ -953,23 +954,25 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
>  	struct vhci_unlink *unlink, *tmp;
>  	unsigned long flags;
>  
> +	if (unlink_list != &vdev->unlink_tx
> +			&& unlink_list != &vdev->unlink_rx) {
> +		pr_err("Invalid list passed to __vhci_cleanup_unlink_list\n");
> +		BUG();

Do not allow the system to crash, that is not ok.

> +		return;

This call makes no sense as you just rebooted the machine :(

Handle errors properly and recover from them and move on.  A single tiny
driver should not take down the whole system.

thanks,

greg k-h