Re: [PATCH] usb: dwc3: qcom: fix NULL pointer dereference on dwc3_qcom_read_usb2_speed

[Johan Hovold <johan@kernel.org>]

On Tue, Aug 13, 2024 at 04:48:47PM +0530, Faisal Hassan wrote:
> Null pointer dereference occurs when accessing 'hcd' to detect speed
> from dwc3_qcom_suspend after the xhci-hcd is unbound.

Why are you unbinding the xhci driver?

> To avoid this issue, ensure to check for NULL in dwc3_qcom_read_usb2_speed.
> 
> echo xhci-hcd.0.auto > /sys/bus/platform/drivers/xhci-hcd/unbind
>   xhci_plat_remove() -> usb_put_hcd() -> hcd_release() -> kfree(hcd)
> 
>   Unable to handle kernel NULL pointer dereference at virtual address
>   0000000000000060
>   Call trace:
>    dwc3_qcom_suspend.part.0+0x17c/0x2d0 [dwc3_qcom]
>    dwc3_qcom_runtime_suspend+0x2c/0x40 [dwc3_qcom]
>    pm_generic_runtime_suspend+0x30/0x44
>    __rpm_callback+0x4c/0x190
>    rpm_callback+0x6c/0x80
>    rpm_suspend+0x10c/0x620
>    pm_runtime_work+0xc8/0xe0
>    process_one_work+0x1e4/0x4f4
>    worker_thread+0x64/0x43c
>    kthread+0xec/0x100
>    ret_from_fork+0x10/0x20
> 
> Fixes: c5f14abeb52b ("usb: dwc3: qcom: fix peripheral and OTG suspend")

This is clearly not the commit that introduced this issue, please be
more careful.

Also make sure to CC the author of any patch introducing a bug so that
they may help with review.

> Cc: stable@vger.kernel.org
> Signed-off-by: Faisal Hassan <quic_faisalh@quicinc.com>
> ---
>  drivers/usb/dwc3/dwc3-qcom.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
> index 88fb6706a18d..0c7846478655 100644
> --- a/drivers/usb/dwc3/dwc3-qcom.c
> +++ b/drivers/usb/dwc3/dwc3-qcom.c
> @@ -319,13 +319,15 @@ static bool dwc3_qcom_is_host(struct dwc3_qcom *qcom)
>  static enum usb_device_speed dwc3_qcom_read_usb2_speed(struct dwc3_qcom *qcom, int port_index)
>  {
>  	struct dwc3 *dwc = platform_get_drvdata(qcom->dwc3);
> -	struct usb_device *udev;
> +	struct usb_device __maybe_unused *udev;
>  	struct usb_hcd __maybe_unused *hcd;
>  
>  	/*
>  	 * FIXME: Fix this layering violation.
>  	 */
>  	hcd = platform_get_drvdata(dwc->xhci);
> +	if (!hcd)
> +		return USB_SPEED_UNKNOWN;

This is just papering over the real issue here which is the layering
violation of having drivers accessing driver data of their children. 

Nothing is preventing the driver data from being deallocated after you
check for NULL here.

I suggest leaving this as is until Bjorn's patches that should address
this properly lands.

>  
>  #ifdef CONFIG_USB
>  	udev = usb_hub_find_child(hcd->self.root_hub, port_index + 1);

Johan