net/sched: flower: Fix null pointer dereference when run tc vlan command

Zahari issued tc vlan command without setting vlan_ethtype, which will
crash kernel. To avoid this, we must check tb[TCA_FLOWER_KEY_VLAN_ETH_TYPE]
is not null before use it.
Also we don't need to dump vlan_ethtype or cvlan_ethtype in this case.

Fixes: d64efd09 ('net/sched: flower: Add supprt for matching on QinQ vlan headers')
Signed-off-by: Jianbo Liu <jianbol@mellanox.com>
Reported-by: Zahari Doychev <zahari.doychev@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_flower.c

@@ -605,6 +605,7 @@ static int fl_set_key(struct net *net, struct nlattr **tb,
 					TCA_FLOWER_KEY_VLAN_PRIO, &key->vlan,
 					&mask->vlan);
 
+			if (tb[TCA_FLOWER_KEY_VLAN_ETH_TYPE]) {
 				ethertype = nla_get_be16(tb[TCA_FLOWER_KEY_VLAN_ETH_TYPE]);
 				if (eth_type_vlan(ethertype)) {
 					fl_set_key_vlan(tb, ethertype,
@@ -620,6 +621,7 @@ static int fl_set_key(struct net *net, struct nlattr **tb,
 					key->basic.n_proto = ethertype;
 					mask->basic.n_proto = cpu_to_be16(~0);
 				}
+			}
 		} else {
 			key->basic.n_proto = ethertype;
 			mask->basic.n_proto = cpu_to_be16(~0);
@@ -1344,6 +1346,7 @@ static int fl_dump(struct net *net, struct tcf_proto *tp, void *fh,
 			 key->cvlan.vlan_tpid)))
 		goto nla_put_failure;
 
+	if (mask->basic.n_proto) {
 		if (mask->cvlan.vlan_tpid) {
 			if (nla_put_be16(skb, TCA_FLOWER_KEY_CVLAN_ETH_TYPE,
 					 key->basic.n_proto))
@@ -1353,6 +1356,7 @@ static int fl_dump(struct net *net, struct tcf_proto *tp, void *fh,
 					 key->basic.n_proto))
 				goto nla_put_failure;
 		}
+	}
 
 	if ((key->basic.n_proto == htons(ETH_P_IP) ||
 	     key->basic.n_proto == htons(ETH_P_IPV6)) &&