Re: [PATCH] driver core: fix race between bus_remove_driver() and dev_driver_uevent()

[Dmitry Torokhov]

On Wed, Oct 14, 2026 at 07:31:19AM +0200, Greg Kroah-Hartman wrote:
> On Tue, Oct 13, 2026 at 08:24:20PM -0700, Dmitry Torokhov wrote:
> > When a device driver is being removed, bus_remove_driver() removes the
> > driver from the bus klist before detaching it from bound devices. If
> > dev_driver_uevent() runs concurrently on another CPU, it may acquire the
> > bus klist lock after the driver has been removed from the list, read the
> > still-valid driver pointer from the device, and access the driver's name
> > while bus_remove_driver() proceeds to free the driver structure.
> > 
> > To close this race window, acquire and immediately release the bus
> > drivers klist lock after all devices have been detached. This ensures
> > that any in-flight uevent generation that observed the driver pointer
> > before device detachment completed finishes reading the driver name
> > before the driver structure is destroyed.
> > 
> > Fixes: 18daa52418e7 ("driver core: fix potential NULL pointer dereference in dev_uevent()")
> > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
> > ---
> > 
> > Extremely unlikely to hit so I would not worry about backporting to
> > stable.
> > 
> >  drivers/base/bus.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> > index d17bd91490ee..8b3aaf451e4f 100644
> > --- a/drivers/base/bus.c
> > +++ b/drivers/base/bus.c
> > @@ -830,6 +830,15 @@ void bus_remove_driver(struct device_driver *drv)
> >  	driver_remove_file(drv, &driver_attr_uevent);
> >  	klist_remove(&drv->p->knode_bus);
> >  	driver_detach(drv);
> > +
> > +	/*
> > +	 * Ensure that any concurrent dev_driver_uevent() that observed
> > +	 * dev->driver before driver_detach() cleared it, finishes
> > +	 * accessing drv->name.
> > +	 */
> > +	scoped_guard(spinlock, &sp->klist_drivers.k_lock) {
> > +	}
> 
> Shouldn't the compiler just no-op this away into nothing?

It better not. Why would it?

Thanks.

-- 
Dmitry