Re: [REGRESSION 5.19] NULL dereference by ucsi_acpi driver

[Linyu Yuan]

On 8/22/2022 9:24 PM, Heikki Krogerus wrote:
> Hi,
>
> On Sat, Aug 20, 2022 at 08:40:52PM +0200, 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.
> > that is any better?
> No, I don't think that's better. Right now I would prefer that we play
> it safe and revert.
>
> The conditions are different in the two places where the ports are
> unregistered in this driver. Therefore I don't think it makes sense
> to use a function like ucsi_unregister_connectors() that tries to
> cover both cases. It will always be a little bit fragile.
>
> Instead we could introduce a function that can be used to remove a
> single port. That would leave the handling of the conditions to the
> callers of the function, but it would still remove the boilerplate.
> That would be much safer IMO.
>
> But to fix this problem, I think we should revert.

but revert will happen on several stable branch, right ?

i think simple fix is good, from my view there is no big differences to 
create a function for a single port.


> thanks,