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

BugLink: https://bugs.launchpad.net/bugs/1828420

[ Upstream commit 3d883026 ]

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

net/core/ethtool.c

@@ -1780,17 +1780,22 @@ static int ethtool_get_strings(struct net_device *dev, void __user *useraddr)
 
 	gstrings.len = ret;
 
+	if (gstrings.len) {
 		data = kcalloc(gstrings.len, ETH_GSTRING_LEN, GFP_USER);
 		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)))
 		goto out;
 	useraddr += sizeof(gstrings);
-	if (copy_to_user(useraddr, data, gstrings.len * ETH_GSTRING_LEN))
+	if (gstrings.len &&
+	    copy_to_user(useraddr, data, gstrings.len * ETH_GSTRING_LEN))
 		goto out;
 	ret = 0;
 
@@ -1878,17 +1883,21 @@ static int ethtool_get_stats(struct net_device *dev, void __user *useraddr)
 		return -EFAULT;
 
 	stats.n_stats = n_stats;
+	if (n_stats) {
 		data = kmalloc(n_stats * sizeof(u64), GFP_USER);
 		if (!data)
 			return -ENOMEM;
 
 		ops->get_ethtool_stats(dev, &stats, data);
+	} else {
+		data = NULL;
+	}
 
 	ret = -EFAULT;
 	if (copy_to_user(useraddr, &stats, sizeof(stats)))
 		goto out;
 	useraddr += sizeof(stats);
-	if (copy_to_user(useraddr, data, stats.n_stats * sizeof(u64)))
+	if (n_stats && copy_to_user(useraddr, data, n_stats * sizeof(u64)))
 		goto out;
 	ret = 0;