Re: [PATCH v2 4/9] usb: dwc3: qcom: fix use-after-free on runtime-PM wakeup

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Thu, Aug 04, 2022 at 05:09:56PM +0200, Johan Hovold wrote:
> The Qualcomm dwc3 runtime-PM implementation checks the xhci
> platform-device pointer in the wakeup-interrupt handler to determine
> whether the controller is in host mode and if so triggers a resume.
> 
> After a role switch in OTG mode the xhci platform-device would have been
> freed and the next wakeup from runtime suspend would access the freed
> memory.
> 
> Note that role switching is executed from a freezable workqueue, which
> guarantees that the pointer is stable during suspend.
> 
> Also note that runtime PM has been broken since commit 2664deb09306
> ("usb: dwc3: qcom: Honor wakeup enabled/disabled state"), which
> incidentally also prevents this issue from being triggered.
> 
> Fixes: a4333c3a6ba9 ("usb: dwc3: Add Qualcomm DWC3 glue driver")
> Cc: stable@vger.kernel.org      # 4.18
> Signed-off-by: Johan Hovold <johan+linaro@kernel.org>

It'd be good to mention the introduction of dwc3_qcom_is_host() function.
Initially I thought it is used in a single place, but going through the rest of
the patches reveals that it is used later on.

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

Thanks,
Mani

> ---
> 
> Changes in v2
>  - new patch
> 
>  drivers/usb/dwc3/dwc3-qcom.c | 14 +++++++++++++-
>  drivers/usb/dwc3/host.c      |  1 +
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
> index e9364141661b..6884026b9fad 100644
> --- a/drivers/usb/dwc3/dwc3-qcom.c
> +++ b/drivers/usb/dwc3/dwc3-qcom.c
> @@ -298,6 +298,14 @@ static void dwc3_qcom_interconnect_exit(struct dwc3_qcom *qcom)
>  	icc_put(qcom->icc_path_apps);
>  }
>  
> +/* Only usable in contexts where the role can not change. */
> +static bool dwc3_qcom_is_host(struct dwc3_qcom *qcom)
> +{
> +	struct dwc3 *dwc = platform_get_drvdata(qcom->dwc3);
> +
> +	return dwc->xhci;
> +}
> +
>  static enum usb_device_speed dwc3_qcom_read_usb2_speed(struct dwc3_qcom *qcom)
>  {
>  	struct dwc3 *dwc = platform_get_drvdata(qcom->dwc3);
> @@ -460,7 +468,11 @@ static irqreturn_t qcom_dwc3_resume_irq(int irq, void *data)
>  	if (qcom->pm_suspended)
>  		return IRQ_HANDLED;
>  
> -	if (dwc->xhci)
> +	/*
> +	 * This is safe as role switching is done from a freezable workqueue
> +	 * and the wakeup interrupts are disabled as part of resume.
> +	 */
> +	if (dwc3_qcom_is_host(qcom))
>  		pm_runtime_resume(&dwc->xhci->dev);
>  
>  	return IRQ_HANDLED;
> diff --git a/drivers/usb/dwc3/host.c b/drivers/usb/dwc3/host.c
> index f56c30cf151e..f6f13e7f1ba1 100644
> --- a/drivers/usb/dwc3/host.c
> +++ b/drivers/usb/dwc3/host.c
> @@ -135,4 +135,5 @@ int dwc3_host_init(struct dwc3 *dwc)
>  void dwc3_host_exit(struct dwc3 *dwc)
>  {
>  	platform_device_unregister(dwc->xhci);
> +	dwc->xhci = NULL;
>  }
> -- 
> 2.35.1
> 

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