From: Li RongQing <lirongqing@baidu.com>
Date: Fri, 29 Mar 2019 09:18:02 +0800
Subject: net: ethtool: not call vzalloc for zero sized memory request
Git-commit: 3d8830266ffc28c16032b859e38a0252e014b631
Patch-mainline: v5.1-rc4
References: networking-stable-19_04_10

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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/core/ethtool.c |   42 ++++++++++++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 14 deletions(-)

--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -1832,11 +1832,16 @@ static int ethtool_get_strings(struct ne
 	WARN_ON_ONCE(!ret);
 
 	gstrings.len = ret;
-	data = vzalloc(gstrings.len * ETH_GSTRING_LEN);
-	if (gstrings.len && !data)
-		return -ENOMEM;
 
-	__ethtool_get_strings(dev, gstrings.string_set, data);
+	if (gstrings.len) {
+		data = vzalloc(gstrings.len * ETH_GSTRING_LEN);
+		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)))
@@ -1932,11 +1937,15 @@ static int ethtool_get_stats(struct net_
 		return -EFAULT;
 
 	stats.n_stats = n_stats;
-	data = vzalloc(n_stats * sizeof(u64));
-	if (n_stats && !data)
-		return -ENOMEM;
 
-	ops->get_ethtool_stats(dev, &stats, data);
+	if (n_stats) {
+		data = vzalloc(n_stats * sizeof(u64));
+		if (!data)
+			return -ENOMEM;
+		ops->get_ethtool_stats(dev, &stats, data);
+	} else {
+		data = NULL;
+	}
 
 	ret = -EFAULT;
 	if (copy_to_user(useraddr, &stats, sizeof(stats)))
@@ -1972,13 +1981,18 @@ static int ethtool_get_phy_stats(struct
 		return -EFAULT;
 
 	stats.n_stats = n_stats;
-	data = vzalloc(n_stats * sizeof(u64));
-	if (n_stats && !data)
-		return -ENOMEM;
 
-	mutex_lock(&phydev->lock);
-	phydev->drv->get_stats(phydev, &stats, data);
-	mutex_unlock(&phydev->lock);
+	if (n_stats) {
+		data = vzalloc(n_stats * sizeof(u64));
+		if (!data)
+			return -ENOMEM;
+
+		mutex_lock(&phydev->lock);
+		phydev->drv->get_stats(phydev, &stats, data);
+		mutex_unlock(&phydev->lock);
+	} else {
+		data = NULL;
+	}
 
 	ret = -EFAULT;
 	if (copy_to_user(useraddr, &stats, sizeof(stats)))