Re: [PATCH 1/2] usbip: Fix seqnum sign extension issue in vhci_tx_urb

[Shuah Khan]

On 12/31/24 09:15, Xiong Nandi wrote:
> The atomic_inc_return function returns an int, while priv->seqnum is an
> unsigned long. So we must cast the result to u32 to prevent potential
> sign extension and size mismatch issues.

How did you find the problem?
> Signed-off-by: Xiong Nandi <xndchn@xxxxxxxxx>
> ---
>   drivers/usb/usbip/vhci_hcd.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
> index b03e5021c25b..f3f260e01791 100644
> --- a/drivers/usb/usbip/vhci_hcd.c
> +++ b/drivers/usb/usbip/vhci_hcd.c
> @@ -675,7 +675,7 @@ static void vhci_tx_urb(struct urb *urb, struct vhci_device *vdev)
>   
>   	spin_lock_irqsave(&vdev->priv_lock, flags);
>   
> -	priv->seqnum = atomic_inc_return(&vhci_hcd->seqnum);
> +	priv->seqnum = (u32)atomic_inc_return(&vhci_hcd->seqnum);

Why does it make sense to cast it to u32?

>   	if (priv->seqnum == 0xffff)
>   		dev_info(&urb->dev->dev, "seqnum max\n");


thanks,
-- Shuah