ethtool: Use kcalloc instead of kmalloc for ethtool_get_strings

[ Upstream commit 077cb37f ]

It seems that kernel memory can leak into userspace by a
kmalloc, ethtool_get_strings, then copy_to_user sequence.

Avoid this by using kcalloc to zero fill the copied buffer.
Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from commit 68c3e59a)
Signed-off-by: Willy Tarreau <w@1wt.eu>

net/core/ethtool.c

@@ -794,7 +794,7 @@ static int ethtool_get_strings(struct net_device *dev, void __user *useraddr)
 		}
 	}
 
-	data = kmalloc(gstrings.len * ETH_GSTRING_LEN, GFP_USER);
+	data = kcalloc(gstrings.len, ETH_GSTRING_LEN, GFP_USER);
 	if (!data)
 		return -ENOMEM;