net: clear heap allocation for ETHTOOL_GRXCLSRLALL

commit ae6df5f9 upstream.

Calling ETHTOOL_GRXCLSRLALL with a large rule_cnt will allocate kernel
heap without clearing it. For the one driver (niu) that implements it,
it will leave the unused portion of heap unchanged and copy the full
contents back to userspace.
Signed-off-by: Kees Cook <kees.cook@canonical.com>
Acked-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

net/core/ethtool.c

@@ -265,7 +265,7 @@ static int ethtool_get_rxnfc(struct net_device *dev,
 	if (info.cmd == ETHTOOL_GRXCLSRLALL) {
 		if (info.rule_cnt > 0) {
 			if (info.rule_cnt <= KMALLOC_MAX_SIZE / sizeof(u32))
-				rule_buf = kmalloc(info.rule_cnt * sizeof(u32),
+				rule_buf = kzalloc(info.rule_cnt * sizeof(u32),
 						   GFP_USER);
 			if (!rule_buf)
 				return -ENOMEM;