Re: [PATCH 1/2] staging: gpib: Fix NULL pointer dereference in detach

[Greg KH <gregkh@linuxfoundation.org>]

On Sat, Jan 18, 2025 at 03:50:45PM +0100, Dave Penkler wrote:
> When the detach function is called after a failed attach
> the usb_dev initialization can cause a NULL pointer
> dereference. This happens when the usb device is not found
> in the attach procedure.
> 
> Remove the usb_dev variable and initialization and change the dev
> in the dev_info message from the usb_dev to the gpib_dev.
> 
> Fixes: fbae7090f30c ("staging: gpib: Update messaging and usb_device refs in agilent_usb")
> Signed-off-by: Dave Penkler <dpenkler@gmail.com>
> ---
>  drivers/staging/gpib/agilent_82357a/agilent_82357a.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/gpib/agilent_82357a/agilent_82357a.c b/drivers/staging/gpib/agilent_82357a/agilent_82357a.c
> index 34d85a1bdb37..2aaccebc3c7b 100644
> --- a/drivers/staging/gpib/agilent_82357a/agilent_82357a.c
> +++ b/drivers/staging/gpib/agilent_82357a/agilent_82357a.c
> @@ -1442,12 +1442,10 @@ static int agilent_82357a_go_idle(gpib_board_t *board)
>  static void agilent_82357a_detach(gpib_board_t *board)
>  {
>  	struct agilent_82357a_priv *a_priv;
> -	struct usb_device *usb_dev;
>  
>  	mutex_lock(&agilent_82357a_hotplug_lock);
>  
>  	a_priv = board->private_data;
> -	usb_dev = interface_to_usbdev(a_priv->bus_interface);
>  	if (a_priv) {
>  		if (a_priv->bus_interface) {
>  			agilent_82357a_go_idle(board);
> @@ -1459,7 +1457,7 @@ static void agilent_82357a_detach(gpib_board_t *board)
>  		agilent_82357a_cleanup_urbs(a_priv);
>  		agilent_82357a_free_private(a_priv);
>  	}
> -	dev_info(&usb_dev->dev, "%s: detached\n", __func__);
> +	dev_info(board->gpib_dev, "%s: detached\n", __func__);

In the future, these dev_info() lines all need to go away as when
drivers work properly, they should be quiet.  I'll take this fix for now
as it's needed, just something to plan on for the future cleanups here.

thanks,

greg k-h