[PATCH nf] netfilter: flowtable: use the vlan id, not the full tci, in the tuple key

[Shuangfeng He <huangya90@gmail.com>]

nf_flow_tuple_encap() stores the skb vlan tag in the encap tuple id
using skb_vlan_tag_get(), which returns the unmasked TCI including
the 3 PCP priority bits. The flowtable entry, however, is programmed
by nf_dev_path_info() with vlan_dev_vlan_id(), a plain 12-bit VID.

When a NIC delivers RX vlan offload skbs with a non-zero priority
(an RTL9617C EPON ONU was observed handing over vid 818 skbs with
tci 0x6332, PCP 3), the runtime lookup key never matches the
programmed entry, so every packet misses the flow table and
software flow offload is silently defeated.

Mask both parse sites to the 12-bit VID so the lookup key matches
for any priority. The in-header variant has the same problem for
frames received with PCP != 0 on a non-offload path.

The egress side is unaffected: nf_flow_encap_push() restores tags
from the programmed tuple id, which never carried priority bits.

Measured on an RTL9617C ONU (PPPoE over VLAN 818 WAN, NATed 6-flow
download over a 1G EPON line), before -> after:

  download throughput      377 Mbps -> 936 Mbps
  CPU0 %soft at that rate    91.5%  ->  70.9%

Fixes: 4cd91f7c290f ("netfilter: flowtable: add vlan support")
Cc: netfilter-devel@vger.kernel.org
Signed-off-by: Shuangfeng He <huangya90@gmail.com>
---
 net/netfilter/nf_flow_table_ip.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nf_flow_table_ip.c b/net/netfilter/nf_flow_table_ip.c
index c8c29a9a1684..2dec15d402ca 100644
--- a/net/netfilter/nf_flow_table_ip.c
+++ b/net/netfilter/nf_flow_table_ip.c
@@ -170,14 +170,14 @@ static void nf_flow_tuple_encap(struct nf_flowtable_ctx *ctx,
 	int i = 0;
 
 	if (skb_vlan_tag_present(skb)) {
-		tuple->encap[i].id = skb_vlan_tag_get(skb);
+		tuple->encap[i].id = skb_vlan_tag_get_id(skb);
 		tuple->encap[i].proto = skb->vlan_proto;
 		i++;
 	}
 	switch (skb->protocol) {
 	case htons(ETH_P_8021Q):
 		veth = (struct vlan_ethhdr *)skb_mac_header(skb);
-		tuple->encap[i].id = ntohs(veth->h_vlan_TCI);
+		tuple->encap[i].id = ntohs(veth->h_vlan_TCI) & VLAN_VID_MASK;
 		tuple->encap[i].proto = skb->protocol;
 		offset += VLAN_HLEN;
 		break;