On Thu, May 13, 2021 at 08:29:01AM +0200, Christophe JAILLET wrote:
> Le 12/05/2021 à 23:44, Russell King - ARM Linux admin a écrit :
> > On Wed, May 12, 2021 at 11:35:38PM +0200, Christophe JAILLET wrote:
> > > 'bus->mii_bus' have been allocated with 'devm_mdiobus_alloc_size()' in the
> > > probe function. So it must not be freed explicitly or there will be a
> > > double free.
> > >
> > > Remove the incorrect 'mdiobus_free' in the remove function.
> >
> > Yes, this looks correct, thanks.
> >
> > Reviewed-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
> >
> > However, there's another issue in this driver that ought to be fixed.
> >
> > If devm_mdiobus_alloc_size() succeeds, but of_mdiobus_register() fails,
> > we continue on to the next bus (which I think is reasonable.) We don't
> > free the bus.
> >
> > When we come to the remove method however, we will call
> > mdiobus_unregister() on this existent but not-registered bus. Surely we
> > don't want to do that?
> >
>
> Hmmm, I don't agree here.
>
> 'nexus' is 'kzalloc()'ed.
> So the pointers in 'buses[]' are all NULL by default.
> We set 'nexus->buses[i] = bus' only when all functions that can fail in the
> loop have been called. (the very last 'break' is when the array is full)
>
> And in the remove function, we have:
> struct cavium_mdiobus *bus = nexus->buses[i];
> if (!bus)
> continue;
>
> So, this looks safe to me.
It isn't safe. Please look closer.
device_for_each_child_node(&pdev->dev, fwn) {
mii_bus = devm_mdiobus_alloc_size(&pdev->dev, sizeof(*bus));
if (!mii_bus)
break;
bus = mii_bus->priv;
bus->mii_bus = mii_bus;
nexus->buses[i] = bus;
This succeeds and sets nexus->buses[i] to a non-NULL value.
err = of_mdiobus_register(bus->mii_bus, node);
if (err)
dev_err(&pdev->dev, "of_mdiobus_register failed\n");
dev_info(&pdev->dev, "Added bus at %llx\n", r.start);
if (i >= ARRAY_SIZE(nexus->buses))
break;
}
If of_mdiobus_register() fails, the bus is not registered, and we just
move on to the next bus, leaving nexus->buses[i] set to a non-NULL
value.
If we now look at the remove code:
for (i = 0; i < ARRAY_SIZE(nexus->buses); i++) {
struct cavium_mdiobus *bus = nexus->buses[i];
if (!bus)
continue;
mdiobus_unregister(bus->mii_bus);
nexus->buses[i] is non-NULL, but the bus is _not_ registered. We end up
calling mdiobus_unregister() on an allocated but _unregistered_ bus.
This is a bug.
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