net: mdio: validate parameter addr in mdiobus_get_phy()

The caller may pass any value as addr, what may result in an out-of-bounds
access to array mdio_map. One existing case is stmmac_init_phy() that
may pass -1 as addr. Therefore validate addr before using it.

Fixes: 7f854420 ("phy: Add API for {un}registering an mdio device to a bus.")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/cdf664ea-3312-e915-73f8-021678d08887@gmail.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/phy/mdio_bus.c

@@ -108,7 +108,12 @@ EXPORT_SYMBOL(mdiobus_unregister_device);
 
 struct phy_device *mdiobus_get_phy(struct mii_bus *bus, int addr)
 {
-	struct mdio_device *mdiodev = bus->mdio_map[addr];
+	struct mdio_device *mdiodev;
+
+	if (addr < 0 || addr >= ARRAY_SIZE(bus->mdio_map))
+		return NULL;
+
+	mdiodev = bus->mdio_map[addr];
 
 	if (!mdiodev)
 		return NULL;