linux-kernel - Re: [PATCH 2/2] USB: dwc3: fix use-after-free on core driver unbind

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Message-ID: <20230608132313.GG5672@thinkpad>
Date:   Thu, 8 Jun 2023 18:53:13 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Krishna Kurapati <quic_kriskura@...cinc.com>,
        linux-usb@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Li Jun <jun.li@....com>,
        Sandeep Maheswaram <quic_c_sanm@...cinc.com>
Subject: Re: [PATCH 2/2] USB: dwc3: fix use-after-free on core driver unbind

On Thu, Jun 08, 2023 at 03:09:27PM +0200, Johan Hovold wrote:
> On Thu, Jun 08, 2023 at 06:32:46PM +0530, Manivannan Sadhasivam wrote:
> > On Wed, Jun 07, 2023 at 12:05:40PM +0200, Johan Hovold wrote:
> > > Some dwc3 glue drivers are currently accessing the driver data of the
> > > child core device directly, which is clearly a bad idea as the child may
> > > not have probed yet or may have been unbound from its driver.
> > > 
> > > As a workaround until the glue drivers have been fixed, clear the driver
> > > data pointer before allowing the glue parent device to runtime suspend
> > > to prevent its driver from accessing data that has been freed during
> > > unbind.
> 
> > > @@ -1929,6 +1929,11 @@ static int dwc3_remove(struct platform_device *pdev)
> > >  	pm_runtime_disable(&pdev->dev);
> > >  	pm_runtime_dont_use_autosuspend(&pdev->dev);
> > >  	pm_runtime_put_noidle(&pdev->dev);
> > > +	/*
> > > +	 * HACK: Clear the driver data, which is currently accessed by parent
> > > +	 * glue drivers, before allowing the parent to suspend.
> > > +	 */
> > > +	platform_set_drvdata(pdev, NULL);
> > 
> > This is required because you have seen the glue driver going to runtime suspend
> > once the below pm_runtime_set_suspended() is completed?
> 
> This is based on analysis of the code. The parent (glue) can not suspend
> while the child (core) is in the active state, but once we set the
> suspended state that could happen.
> 

I could see that the driver core is setting drvdata to NULL during
device_unbind_cleanup(), so not sure if this scenario could be met otherwise it
will be redundant.

- Mani


> > >  
> > >  	dwc3_free_event_buffers(dwc);
> 
> Johan

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