Re: [PATCH] net: hso: fix NULL-deref on disconnect regression

[Anirudh Rayabharam]

On Mon, Apr 26, 2021 at 10:11:49AM +0200, Johan Hovold wrote:
> Commit 8a12f8836145 ("net: hso: fix null-ptr-deref during tty device
> unregistration") fixed the racy minor allocation reported by syzbot, but
> introduced an unconditional NULL-pointer dereference on every disconnect
> instead.
> 
> Specifically, the serial device table must no longer be accessed after
> the minor has been released by hso_serial_tty_unregister().
> 
> Fixes: 8a12f8836145 ("net: hso: fix null-ptr-deref during tty device unregistration")
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: Anirudh Rayabharam <mail@xxxxxxxxxxxxx>
> Reported-by: Leonardo Antoniazzi <leoanto@xxxxxxxx>
> Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
> ---
>  drivers/net/usb/hso.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/usb/hso.c b/drivers/net/usb/hso.c
> index 9bc58e64b5b7..3ef4b2841402 100644
> --- a/drivers/net/usb/hso.c
> +++ b/drivers/net/usb/hso.c
> @@ -3104,7 +3104,7 @@ static void hso_free_interface(struct usb_interface *interface)
>  			cancel_work_sync(&serial_table[i]->async_put_intf);
>  			cancel_work_sync(&serial_table[i]->async_get_intf);
>  			hso_serial_tty_unregister(serial);
> -			kref_put(&serial_table[i]->ref, hso_serial_ref_free);
> +			kref_put(&serial->parent->ref, hso_serial_ref_free);
>  		}
>  	}

Ah, my bad. Thanks Johan for the fix!

Reviewed-by: Anirudh Rayabharam <mail@xxxxxxxxxxxxx>

	- Anirudh.