net/ncsi: handle overflow when incrementing mac address

Previously BMC's MAC address is calculated by simply adding 1 to the
last byte of network controller's MAC address, and it produces incorrect
result when network controller's MAC address ends with 0xFF.

The problem can be fixed by calling eth_addr_inc() function to increment
MAC address; besides, the MAC address is also validated before assigning
to BMC.

Fixes: cb10c7c0dfd9 ("net/ncsi: Add NCSI Broadcom OEM command")
Signed-off-by: Tao Ren <[e-mail]>
Acked-by: Jakub Kicinski <[e-mail]>
Acked-by: Samuel Mendoza-Jonas <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/etherdevice.h

···
 }
 
 /**
+ * eth_addr_inc() - Increment the given MAC address.
+ * @addr: Pointer to a six-byte array containing Ethernet address to increment.
+ */
+static inline void eth_addr_inc(u8 *addr)
+{
+	u64 u = ether_addr_to_u64(addr);
+
+	u++;
+	u64_to_ether_addr(u, addr);
+}
+
+/**
  * is_etherdev_addr - Tell if given Ethernet address belongs to the device.
  * @dev: Pointer to a device structure
  * @addr: Pointer to a six-byte array containing the Ethernet address

net/ncsi/ncsi-rsp.c

···
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/netdevice.h>
+#include <linux/etherdevice.h>
 #include <linux/skbuff.h>
 
 #include <net/ncsi.h>
···
 	ndev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
 	memcpy(saddr.sa_data, &rsp->data[BCM_MAC_ADDR_OFFSET], ETH_ALEN);
 	/* Increase mac address by 1 for BMC's address */
-	saddr.sa_data[ETH_ALEN - 1]++;
+	eth_addr_inc((u8 *)saddr.sa_data);
+	if (!is_valid_ether_addr((const u8 *)saddr.sa_data))
+		return -ENXIO;
+
 	ret = ops->ndo_set_mac_address(ndev, &saddr);
 	if (ret < 0)
 		netdev_warn(ndev, "NCSI: 'Writing mac address to device failed\n");