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Date:   Sat, 6 Aug 2022 18:08:51 +0200
From:   Johan Hovold <johan@kernel.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc:     Johan Hovold <johan+linaro@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Felipe Balbi <balbi@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Konrad Dybcio <konrad.dybcio@somainline.org>,
        Krishna Kurapati <quic_kriskura@quicinc.com>,
        Stephen Boyd <swboyd@chromium.org>,
        Doug Anderson <dianders@chromium.org>,
        Matthias Kaehlcke <mka@chromium.org>,
        Pavankumar Kondeti <quic_pkondeti@quicinc.com>,
        quic_ppratap@quicinc.com, quic_vpulyala@quicinc.com,
        linux-arm-msm@vger.kernel.org, linux-usb@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
Subject: Re: [PATCH v2 4/9] usb: dwc3: qcom: fix use-after-free on runtime-PM
 wakeup
Message-ID: <Yu6SE1wKXk6/qT9Z@hovoldconsulting.com>
References: <20220804151001.23612-1-johan+linaro@kernel.org>
 <20220804151001.23612-5-johan+linaro@kernel.org>
 <20220806143311.GE14384@thinkpad>
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On Sat, Aug 06, 2022 at 08:03:11PM +0530, Manivannan Sadhasivam wrote:
> 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.

I think the helper is warranted on its own as it serves as documentation
of the underlying assumptions that this code relies on.

> > +/* 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

Johan