Re: [REGRESSION 5.19] NULL dereference by ucsi_acpi driver

[Linyu Yuan]

On 8/21/2022 2:40 AM, Greg Kroah-Hartman wrote:
> On Fri, Aug 19, 2022 at 06:32:43PM +0200, Takashi Iwai wrote:
> > Hi,
> >
> > we've got multiple reports about 5.19 kernel starting crashing after
> > some time, and this turned out to be triggered by ucsi_acpi driver.
> > The details are found in:
> >    https://bugzilla.suse.com/show_bug.cgi?id=1202386
> >
> > The culprit seems to be the commit 87d0e2f41b8c
> >      usb: typec: ucsi: add a common function ucsi_unregister_connectors()
> Adding Heikki to the thread...
>
> >      
> > This commit looks as if it were a harmless cleanup, but this failed in
> > a subtle way.  Namely, in the error scenario, the driver gets an error
> > at ucsi_register_altmodes(), and goes to the error handling to release
> > the resources.  Through this refactoring, the release part was unified
> > to a funciton ucsi_unregister_connectors().  And there, it has a NULL
> > check of con->wq, and it bails out the loop if it's NULL.
> > Meanwhile, ucsi_register_port() itself still calls destroy_workqueue()
> > and clear con->wq at its error path.  This ended up in the leftover
> > power supply device with the uninitialized / cleared device.
> >
> > It was confirmed that the problem could be avoided by a simple
> > revert.
> I'll be glad to revert this now, unless Heikki thinks:
>
> > I guess another fix could be removing the part clearing con->wq, i.e.
> >
> > --- a/drivers/usb/typec/ucsi/ucsi.c
> > +++ b/drivers/usb/typec/ucsi/ucsi.c
> > @@ -1192,11 +1192,6 @@ static int ucsi_register_port(struct ucsi *ucsi, int index)
> >   out_unlock:
> >   	mutex_unlock(&con->lock);
> >   
> > -	if (ret && con->wq) {
> > -		destroy_workqueue(con->wq);
> > -		con->wq = NULL;
> > -	}
> > -
> >   	return ret;
> >   }
> >   
> >
> > ... but it's totally untested and I'm not entirely sure whether it's
> > better.

this part is original code, yes, but when I make the change you mentioned,

as in the function ucsi_unregister_connectors(),  just use con->wq to 
represent which connector initialized previous,

indeed if we clear it in ucsi_register_port(), something will left unclear.

please send a patch to fix it.

I think your change is good.

> that is any better?
>
> thanks,
>
> greg k-h