linux-kernel - Re: [PATCH] USB: core: Fix potental Null Pointer dereference

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Date:   Thu, 10 Oct 2019 07:20:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Yizhuo <yzhai003@....edu>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Douglas Anderson <dianders@...omium.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Jan-Marek Glogowski <glogow@...home.de>,
        Mathieu Malaterre <malat@...ian.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: core: Fix potental Null Pointer dereference

On Wed, Oct 09, 2019 at 06:02:02PM -0700, Yizhuo wrote:
> Inside function usb_device_is_owned(), usb_hub_to_struct_hub()
> could return NULL but there's no check before its dereference,
> which is potentially unsafe.
> 
> Signed-off-by: Yizhuo <yzhai003@....edu>
> ---
>  drivers/usb/core/hub.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 236313f41f4a..8d628c8e0c1b 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -1977,7 +1977,7 @@ bool usb_device_is_owned(struct usb_device *udev)
>  	if (udev->state == USB_STATE_NOTATTACHED || !udev->parent)
>  		return false;
>  	hub = usb_hub_to_struct_hub(udev->parent);
> -	return !!hub->ports[udev->portnum - 1]->port_owner;
> +	return hub && !!hub->ports[udev->portnum - 1]->port_owner;

How can hub ever not be valid?

thanks,

greg k-h