net/mlx5: fix flows when VXLAN tunnel is 0

Fix a strange behavior from the NIC, when the flow starts with a VXLAN
layer with a VNI equals to zero all the traffic will match within this
rule.

Fixes: 2e709b6aa0f5 ("net/mlx5: support VXLAN flow item")
Cc: stable@dpdk.org

Signed-off-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>
Acked-by: Yongseok Koh <yskoh@mellanox.com>

doc/guides/nics/mlx5.rst

@@ -129,6 +129,8 @@ Limitations
   is set to multi-packet send or Enhanced multi-packet send. Otherwise it must have
   less than 50 segments.
 - Count action for RTE flow is only supported in Mellanox OFED 4.2.
+- Flows with a VXLAN Network Identifier equal (or ends to be equal)
+  to 0 are not supported.
 
 Configuration
 -------------

drivers/net/mlx5/mlx5_flow.c

@@ -1155,7 +1155,7 @@ priv_flow_convert(struct priv *priv,
 					 cur_item->mask),
 					parser);
 		if (ret) {
-			rte_flow_error_set(error, ENOTSUP,
+			rte_flow_error_set(error, ret,
 					   RTE_FLOW_ERROR_TYPE_ITEM,
 					   items, "item not supported");
 			goto exit_free;
@@ -1602,6 +1602,16 @@ mlx5_flow_create_vxlan(const struct rte_flow_item *item,
 		/* Remove unwanted bits from values. */
 		vxlan.val.tunnel_id &= vxlan.mask.tunnel_id;
 	}
+	/*
+	 * Tunnel id 0 is equivalent as not adding a VXLAN layer, if only this
+	 * layer is defined in the Verbs specification it is interpreted as
+	 * wildcard and all packets will match this rule, if it follows a full
+	 * stack layer (ex: eth / ipv4 / udp), all packets matching the layers
+	 * before will also match this rule.
+	 * To avoid such situation, VNI 0 is currently refused.
+	 */
+	if (!vxlan.val.tunnel_id)
+		return EINVAL;
 	mlx5_flow_create_copy(parser, &vxlan, size);
 	return 0;
 }