net: ethtool: not call vzalloc for zero sized memory request

NULL or ZERO_SIZE_PTR will be returned for zero sized memory
request, and derefencing them will lead to a segfault

so it is unnecessory to call vzalloc for zero sized memory
request and not call functions which maybe derefence the
NULL allocated memory

this also fixes a possible memory leak if phy_ethtool_get_stats
returns error, memory should be freed before exit
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Reviewed-by: Wang Li <wangli39@baidu.com>
Reviewed-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/ethtool.c

@@ -1797,11 +1797,16 @@ static int ethtool_get_strings(struct net_device *dev, void __user *useraddr)
 	WARN_ON_ONCE(!ret);
 
 	gstrings.len = ret;
+
+	if (gstrings.len) {
 		data = vzalloc(array_size(gstrings.len, ETH_GSTRING_LEN));
-	if (gstrings.len && !data)
+		if (!data)
 			return -ENOMEM;
 
 		__ethtool_get_strings(dev, gstrings.string_set, data);
+	} else {
+		data = NULL;
+	}
 
 	ret = -EFAULT;
 	if (copy_to_user(useraddr, &gstrings, sizeof(gstrings)))
@@ -1897,11 +1902,15 @@ static int ethtool_get_stats(struct net_device *dev, void __user *useraddr)
 		return -EFAULT;
 
 	stats.n_stats = n_stats;
+
+	if (n_stats) {
 		data = vzalloc(array_size(n_stats, sizeof(u64)));
-	if (n_stats && !data)
+		if (!data)
 			return -ENOMEM;
-
 		ops->get_ethtool_stats(dev, &stats, data);
+	} else {
+		data = NULL;
+	}
 
 	ret = -EFAULT;
 	if (copy_to_user(useraddr, &stats, sizeof(stats)))
@@ -1941,17 +1950,22 @@ static int ethtool_get_phy_stats(struct net_device *dev, void __user *useraddr)
 		return -EFAULT;
 
 	stats.n_stats = n_stats;
+
+	if (n_stats) {
 		data = vzalloc(array_size(n_stats, sizeof(u64)));
-	if (n_stats && !data)
+		if (!data)
 			return -ENOMEM;
 
 		if (dev->phydev && !ops->get_ethtool_phy_stats) {
 			ret = phy_ethtool_get_stats(dev->phydev, &stats, data);
 			if (ret < 0)
-			return ret;
+				goto out;
 		} else {
 			ops->get_ethtool_phy_stats(dev, &stats, data);
 		}
+	} else {
+		data = NULL;
+	}
 
 	ret = -EFAULT;
 	if (copy_to_user(useraddr, &stats, sizeof(stats)))