net: ethtool: Return -EOPNOTSUPP if user space tries to read EEPROM with lengh 0

If a driver supports reading EEPROM but no EEPROM is installed in the system,
the driver's get_eeprom_len function returns 0. ethtool will subsequently
try to read that zero-length EEPROM anyway. If the driver does not support
EEPROM access at all, this operation will return -EOPNOTSUPP. If the driver
does support EEPROM access but no EEPROM is installed, the operation will
return -EINVAL. Return -EOPNOTSUPP in both cases for consistency.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/ethtool.c

@@ -1036,7 +1036,8 @@ static int ethtool_get_eeprom(struct net_device *dev, void __user *useraddr)
 {
 	const struct ethtool_ops *ops = dev->ethtool_ops;
 
-	if (!ops->get_eeprom || !ops->get_eeprom_len)
+	if (!ops->get_eeprom || !ops->get_eeprom_len ||
+	    !ops->get_eeprom_len(dev))
 		return -EOPNOTSUPP;
 
 	return ethtool_get_any_eeprom(dev, useraddr, ops->get_eeprom,
@@ -1052,7 +1053,8 @@ static int ethtool_set_eeprom(struct net_device *dev, void __user *useraddr)
 	u8 *data;
 	int ret = 0;
 
-	if (!ops->set_eeprom || !ops->get_eeprom_len)
+	if (!ops->set_eeprom || !ops->get_eeprom_len ||
+	    !ops->get_eeprom_len(dev))
 		return -EOPNOTSUPP;
 
 	if (copy_from_user(&eeprom, useraddr, sizeof(eeprom)))