[PATCH][v2] net: ethtool: not call vzalloc for zero sized memory request

[Li RongQing]

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 <lirongq...@baidu.com>
Reviewed-by: Wang Li <wangl...@baidu.com>
---
v1->v2: not call get_ethtool_stats if n_stats is 0 

 net/core/ethtool.c | 46 ++++++++++++++++++++++++++++++----------------
 1 file changed, 30 insertions(+), 16 deletions(-)

diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index b1eb32419732..36ed619faf36 100644
--- a/net/core/ethtool.c
+++ b/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;
-       data = vzalloc(array_size(gstrings.len, ETH_GSTRING_LEN));
-       if (gstrings.len && !data)
-               return -ENOMEM;
 
-       __ethtool_get_strings(dev, gstrings.string_set, data);
+       if (gstrings.len) {
+               data = vzalloc(array_size(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)))
@@ -1897,11 +1902,15 @@ static int ethtool_get_stats(struct net_device *dev, 
void __user *useraddr)
                return -EFAULT;
 
        stats.n_stats = n_stats;
-       data = vzalloc(array_size(n_stats, sizeof(u64)));
-       if (n_stats && !data)
-               return -ENOMEM;
 
-       ops->get_ethtool_stats(dev, &stats, data);
+       if (n_stats) {
+               data = vzalloc(array_size(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)))
@@ -1941,16 +1950,21 @@ static int ethtool_get_phy_stats(struct net_device 
*dev, void __user *useraddr)
                return -EFAULT;
 
        stats.n_stats = n_stats;
-       data = vzalloc(array_size(n_stats, sizeof(u64)));
-       if (n_stats && !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;
+       if (n_stats) {
+               data = vzalloc(array_size(n_stats, sizeof(u64)));
+               if (!data)
+                       return -ENOMEM;
+
+               if (dev->phydev && !ops->get_ethtool_phy_stats) {
+                       ret = phy_ethtool_get_stats(dev->phydev, &stats, data);
+                       if (ret < 0)
+                               goto out;
+               } else {
+                       ops->get_ethtool_phy_stats(dev, &stats, data);
+               }
        } else {
-               ops->get_ethtool_phy_stats(dev, &stats, data);
+               data = NULL;
        }
 
        ret = -EFAULT;
-- 
2.16.2