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

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

On Tue, Oct 13, 2026 at 11:11:33PM -0700, Dmitry Torokhov wrote:
> 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@gmail.com>
> > > ---
> > > 
> > > 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?

Sorry, early morning before my coffee had kicked in, I was thinking a
simple lock/unlock pair without any data in the middle might be compiled
away...

Still feels odd though I don't have a better idea.

greg k-h