Re: [REGRESSION 5.19] NULL dereference by ucsi_acpi driver

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Aug 30, 2022 at 02:51:54PM +0200, Greg Kroah-Hartman wrote:
> On Mon, Aug 22, 2022 at 10:44:26AM +0800, Linyu Yuan wrote:
> > 
> > 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.
> 
> Ok, can someone send me a patch to apply to the tree for this?

Oh nevermind, I already have the revert in my tree, sorry for the noise.

greg k-h