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

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

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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