flow_dissector: For stripped vlan, get vlan info from skb->vlan_tci

Early in the datapath skb_vlan_untag function is called, stripped
the vlan from the skb and set skb->vlan_tci and skb->vlan_proto fields.

The current dissection doesn't handle stripped vlan packets correctly.
In some flows, vlan doesn't exist in skb->data anymore when applying
flow dissection on the skb, fix that.

In case vlan info wasn't stripped before applying flow_dissector (RPS
flow for example), or in case of skb with multiple vlans (e.g. 802.1ad),
get the vlan info from skb->data. The flow_dissector correctly skips
any number of vlans and stores only the first level vlan.

Fixes: 0744dd00c1b1 ('net: introduce skb_flow_dissect()')
Signed-off-by: Hadar Hen Zion <hadarh@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/flow_dissector.c

@@ -119,12 +119,14 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 	struct flow_dissector_key_ports *key_ports;
 	struct flow_dissector_key_tags *key_tags;
 	struct flow_dissector_key_keyid *key_keyid;
+	bool skip_vlan = false;
 	u8 ip_proto = 0;
 	bool ret = false;
 
 	if (!data) {
 		data = skb->data;
-		proto = skb->protocol;
+		proto = skb_vlan_tag_present(skb) ?
+			 skb->vlan_proto : skb->protocol;
 		nhoff = skb_network_offset(skb);
 		hlen = skb_headlen(skb);
 	}
@@ -243,23 +245,39 @@ ipv6:
 	case htons(ETH_P_8021AD):
 	case htons(ETH_P_8021Q): {
 		const struct vlan_hdr *vlan;
-		struct vlan_hdr _vlan;
 
-		vlan = __skb_header_pointer(skb, nhoff, sizeof(_vlan), data, hlen, &_vlan);
-		if (!vlan)
-			goto out_bad;
+		if (skb_vlan_tag_present(skb))
+			proto = skb->protocol;
+
+		if (!skb_vlan_tag_present(skb) ||
+		    proto == cpu_to_be16(ETH_P_8021Q) ||
+		    proto == cpu_to_be16(ETH_P_8021AD)) {
+			struct vlan_hdr _vlan;
+
+			vlan = __skb_header_pointer(skb, nhoff, sizeof(_vlan),
+						    data, hlen, &_vlan);
+			if (!vlan)
+				goto out_bad;
+			proto = vlan->h_vlan_encapsulated_proto;
+			nhoff += sizeof(*vlan);
+			if (skip_vlan)
+				goto again;
+		}
 
+		skip_vlan = true;
 		if (dissector_uses_key(flow_dissector,
 				       FLOW_DISSECTOR_KEY_VLANID)) {
 			key_tags = skb_flow_dissector_target(flow_dissector,
 							     FLOW_DISSECTOR_KEY_VLANID,
 							     target_container);
 
-			key_tags->vlan_id = skb_vlan_tag_get_id(skb);
+			if (skb_vlan_tag_present(skb))
+				key_tags->vlan_id = skb_vlan_tag_get_id(skb);
+			else
+				key_tags->vlan_id = ntohs(vlan->h_vlan_TCI) &
+					VLAN_VID_MASK;
 		}
 
-		proto = vlan->h_vlan_encapsulated_proto;
-		nhoff += sizeof(*vlan);
 		goto again;
 	}
 	case htons(ETH_P_PPP_SES): {