net: hns3: fix access null pointer issue when set tx-buf-size as 0

mainline inclusion
from mainline-origin
commit a4fe9b6d
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I56XHY
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a4fe9b6db6f9

----------------------------------------------------------------------

When set tx-buf-size as 0 by ethtool, hns3_init_tx_spare_buffer()
will return directly and priv->ring->tx_spare->len is uninitialized,
then print function access priv->ring->tx_spare->len will cause
this issue.

When set tx-buf-size as 0 by ethtool, the print function will
print 0 directly and not access priv->ring->tx_spare->len.

Fixes: 2373b35c ("net: hns3: add log for setting tx spare buf size")
Signed-off-by: NHao Chen <chenhao288@hisilicon.com>
Signed-off-by: NGuangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NJiantao Xiao <xiaojiantao1@h-partners.com>
Reviewed-by: NYue Haibing <yuehaibing@huawei.com>
Reviewed-by: NJian Shen <shenjian15@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/net/ethernet/hisilicon/hns3/hns3_ethtool.c

@@ -1902,8 +1902,11 @@ static int hns3_set_tunable(struct net_device *netdev,
 			return ret;
 		}
 
-		netdev_info(netdev, "the active tx spare buf size is %u, due to page order\n",
-			    priv->ring->tx_spare->len);
+		if (!priv->ring->tx_spare)
+			netdev_info(netdev, "the active tx spare buf size is 0, disable tx spare buffer\n");
+		else
+			netdev_info(netdev, "the active tx spare buf size is %u, due to page order\n",
+				    priv->ring->tx_spare->len);
 
 		break;
 	default: