Re: [PATCH v2 1/4] PCI: s390: Fix use-after-free of PCI resources with per-function hotplug

Andy Shevchenko
2023-04-17T10:11:23Z

On Mon, Apr 17, 2023 at 10:46 AM Lukas Wunner <lukas@wunner.de> wrote:
> On Mon, Mar 06, 2023 at 04:10:11PM +0100, Niklas Schnelle wrote:

...

> > +void pci_bus_remove_resource(struct pci_bus *bus, struct resource *res)
> > +{
> > + struct pci_bus_resource *bus_res, *tmp;
> > + int i;
> > +
> > + for (i = 0; i < PCI_BRIDGE_RESOURCE_NUM; i++) {
> > + if (bus->resource[i] == res) {
> > + bus->resource[i] = NULL;
> > + return;
> > + }
> > + }
> > +
> > + list_for_each_entry_safe(bus_res, tmp, &bus->resources, list) {
> > + if (bus_res->res == res) {
> > + list_del(&bus_res->list);
> > + kfree(bus_res);
> > + return;
> > + }
> > + }
> > +}
>
> I realize this has already been applied so s390.git/master,
> but nevertheless would like to point out there's a handy
> pci_bus_for_each_resource() helper which could have been
> used here instead of the for-loop.

Actually in this case it's not possible. The above code nullifies the
matched resource or removes it from the list. We don't have any good
iterator inside pci_bus_for_each_resource() to do the latter.

There might be other places in the kernel code where something like
above is used and we can split a separate helper exactly for matching
cases, but with the above context I dunno we need to do anything right
now.

P.S. Thanks for Cc'ing me.

--
With Best Regards,
Andy Shevchenko