[PATCH RFT v2 net-next] net: mdio: ensure the type of mdio devices match mdio drivers

On the MDIO bus, we have PHYLIB devices and drivers, and we have non-
PHYLIB devices and drivers. PHYLIB devices are MDIO devices that are
wrapped with a struct phy_device.

Trying to bind a MDIO device with a PHYLIB driver results in out-of-
bounds accesses as we attempt to access struct phy_device members. So,
let's prevent this by ensuring that the type of the MDIO device
(indicated by the MDIO_DEVICE_FLAG_PHY flag) matches the type of the
MDIO driver (indicated by the MDIO_DEVICE_IS_PHY flag.)

Link: https://lore.kernel.org/r/2b1dc053-8c9a-e3e4-b450-eecdfca3fe16@gmail.com (local)
Signed-off-by: Russell King (Oracle) <redacted>
---
Tested locally in SolidRun Clearfog, DSA switch and PHY get probed
correctly. Further testing welcomed.

v2: dead christmas tree ordering.

 drivers/net/phy/mdio_bus.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index 53f034fc2ef7..3a36b463c22a 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c

@@ -938,8 +938,14 @@ EXPORT_SYMBOL_GPL(mdiobus_modify);
  */
 static int mdio_bus_match(struct device *dev, struct device_driver *drv)
 {
+	struct mdio_driver *mdiodrv = to_mdio_driver(drv);
 	struct mdio_device *mdio = to_mdio_device(dev);
 
+	/* Both the driver and device must type-match */
+	if (!(mdiodrv->mdiodrv.flags & MDIO_DEVICE_IS_PHY) !=
+	    !(mdio->flags & MDIO_DEVICE_FLAG_PHY))
+		return 0;
+
 	if (of_driver_match_device(dev, drv))
 		return 1;
 

-- 
2.30.2