linux-kernel - Re: [PATCH 3/5] usb: dwc3: qcom: Fix null ptr access during runtime

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Message-ID: <20230328100859.GE5695@thinkpad>
Date:   Tue, 28 Mar 2023 15:38:59 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     andersson@...nel.org, Thinh.Nguyen@...opsys.com,
        gregkh@...uxfoundation.org, mathias.nyman@...el.com,
        konrad.dybcio@...aro.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 3/5] usb: dwc3: qcom: Fix null ptr access during
 runtime_suspend()

On Tue, Mar 28, 2023 at 11:51:53AM +0200, Johan Hovold wrote:
> On Tue, Mar 28, 2023 at 03:17:18PM +0530, Manivannan Sadhasivam wrote:
> > On Tue, Mar 28, 2023 at 11:23:32AM +0200, Johan Hovold wrote:
> > > On Sat, Mar 25, 2023 at 10:22:15PM +0530, Manivannan Sadhasivam wrote:
> 
> > > >  static int dwc3_qcom_suspend(struct dwc3_qcom *qcom, bool wakeup)
> > > >  {
> > > > +	struct dwc3 *dwc = platform_get_drvdata(qcom->dwc3);
> > > >  	u32 val;
> > > >  	int i, ret;
> > > >  
> > > > -	if (qcom->is_suspended)
> > > > +	if (qcom->is_suspended || !dwc)
> > > >  		return 0;
> > > 
> > > I think we should try to keep the layering violations confined to the
> > > helper functions. So how about amending dwc3_qcom_is_host() and check
> > > for NULL before dereferencing the xhci pointer?
> > > 
> > > If the dwc3 driver hasn't probed yet, we're clearly not in host mode
> > > either...
> > 
> > Well, that's what I initially did but then I reverted to this approach as
> > returning true/false from dwc3_qcom_is_host() based on the pointer availability
> > doesn't sound right.
> > 
> > For example, if we return true then it implies that the driver is in host mode
> > which is logically wrong (before dwc3 probe) even though there is no impact.
> 
> No, you should return false of course as we are *not* in host mode as I
> mentioned above.
> 

Yes, but I interpreted it as "we are in device mode" in that case. But looking
at it again, I think it just conveys that the controller is not in host mode
only.

- Mani

> Johan

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