net/sched: act_vlan: Fix modify to allow 0

Currently vlan modification action checks existence of vlan priority by
comparing it to 0. Therefore it is impossible to modify existing vlan
tag to have priority 0.

For example, the following tc command will change the vlan id but will
not affect vlan priority:

tc filter add dev eth1 ingress matchall action vlan modify id 300 \
        priority 0 pipe mirred egress redirect dev eth2

The incoming packet on eth1:

ethertype 802.1Q (0x8100), vlan 200, p 4, ethertype IPv4

will be changed to:

ethertype 802.1Q (0x8100), vlan 300, p 4, ethertype IPv4

although the user has intended to have p == 0.

The fix is to add tcfv_push_prio_exists flag to struct tcf_vlan_params
and rely on it when deciding to set the priority.

Fixes: 45a497f2d149a4a8061c (net/sched: act_vlan: Introduce TCA_VLAN_ACT_MODIFY vlan action)
Signed-off-by: Boris Sukholitko <boris.sukholitko@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/net/tc_act/tc_vlan.h b/include/net/tc_act/tc_vlan.h
index f051046ba034..f94b8bc26f9e 100644
--- a/include/net/tc_act/tc_vlan.h
+++ b/include/net/tc_act/tc_vlan.h
@@ -16,6 +16,7 @@ struct tcf_vlan_params {
 	u16               tcfv_push_vid;
 	__be16            tcfv_push_proto;
 	u8                tcfv_push_prio;
+	bool              tcfv_push_prio_exists;
 	struct rcu_head   rcu;
 };