net/mdiobus: Fix potential out-of-bounds read/write access

net/mdiobus: Fix potential out-of-bounds read/write access

When using publicly available tools like 'mdio-tools' to read/write data
from/to network interface and its PHY via mdiobus, there is no verification of
parameters passed to the ioctl and it accepts any mdio address.
Currently there is support for 32 addresses in kernel via PHY_MAX_ADDR define,
but it is possible to pass higher value than that via ioctl.
While read/write operation should generally fail in this case,
mdiobus provides stats array, where wrong address may allow out-of-bounds
read/write.

Fix that by adding address verification before read/write operation.
While this excludes this access from any statistics, it improves security of
read/write operation.

Fixes: 080bb352fad00 ("net: phy: Maintain MDIO device and bus statistics")
Signed-off-by: Jakub Raczynski <j.raczynski@samsung.com>
Reported-by: Wenjing Shan <wenjing.shan@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>