ethtool: check the return value of get_regs_len

The return type for get_regs_len in struct ethtool_ops is int,
the hns3 driver may return error when failing to get the regs
len by sending cmd to firmware.
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/ethtool.c

@@ -793,8 +793,13 @@ static noinline_for_stack int ethtool_get_drvinfo(struct net_device *dev,
 		if (rc >= 0)
 			info.n_priv_flags = rc;
 	}
-	if (ops->get_regs_len)
-		info.regdump_len = ops->get_regs_len(dev);
+	if (ops->get_regs_len) {
+		int ret = ops->get_regs_len(dev);
+
+		if (ret > 0)
+			info.regdump_len = ret;
+	}
+
 	if (ops->get_eeprom_len)
 		info.eedump_len = ops->get_eeprom_len(dev);
 
@@ -1337,6 +1342,9 @@ static int ethtool_get_regs(struct net_device *dev, char __user *useraddr)
 		return -EFAULT;
 
 	reglen = ops->get_regs_len(dev);
+	if (reglen <= 0)
+		return reglen;
+
 	if (regs.len > reglen)
 		regs.len = reglen;