linux-kernel - [PATCH net v2 2/2] net/ncsi: handle overflow when incrementing mac address

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Date:   Tue, 23 Apr 2019 14:20:48 -0700
From:   Tao Ren <taoren@...com>
To:     "David S . Miller" <davem@...emloft.net>,
        Maxim Mikityanskiy <maximmi@...lanox.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Samuel Mendoza-Jonas <sam@...dozajonas.com>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>, <openbmc@...ts.ozlabs.org>
CC:     Tao Ren <taoren@...com>
Subject: [PATCH net v2 2/2] 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 "net_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 <taoren@...com>
---
 net/ncsi/ncsi-rsp.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Changes in v2:
 - increment MAC address by calling net_addr_inc function.
 - validate MAC address before assigning to BMC.

diff --git a/net/ncsi/ncsi-rsp.c b/net/ncsi/ncsi-rsp.c
index dc07fcc7938e..802db01e3075 100644
--- a/net/ncsi/ncsi-rsp.c
+++ b/net/ncsi/ncsi-rsp.c
@@ -11,6 +11,7 @@
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/netdevice.h>
+#include <linux/etherdevice.h>
 #include <linux/skbuff.h>
 
 #include <net/ncsi.h>
@@ -667,7 +668,10 @@ static int ncsi_rsp_handler_oem_bcm_gma(struct ncsi_request *nr)
 	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");
-- 
2.17.1