net: usb: rtl8150: don't incorrectly assign random MAC addresses

In set_ethernet_addr(), if get_registers() succeeds, the ethernet address
that was read must be copied over. Otherwise, a random ethernet address
must be assigned.

get_registers() returns 0 if successful, and negative error number
otherwise. However, in set_ethernet_addr(), this return value is
incorrectly checked.

Since this return value will never be equal to sizeof(node_id), a
random MAC address will always be generated and assigned to the
device; even in cases when get_registers() is successful.

Correctly modifying the condition that checks if get_registers() was
successful or not fixes this problem, and copies the ethernet address
appropriately.

Fixes: b2a0f274 ("net: rtl8150: Use the new usb control message API.")
Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
Link: https://lore.kernel.org/r/20201011173030.141582-1-anant.thazhemadam@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/usb/rtl8150.c

@@ -261,7 +261,7 @@ static void set_ethernet_addr(rtl8150_t *dev)
 
 	ret = get_registers(dev, IDR, sizeof(node_id), node_id);
 
-	if (ret == sizeof(node_id)) {
+	if (!ret) {
 		ether_addr_copy(dev->netdev->dev_addr, node_id);
 	} else {
 		eth_hw_addr_random(dev->netdev);