name : sock-parse-dns.lua #!/usr/bin/env bcc-lua --[[ Copyright 2016 Marek Vavrusa <mvavrusa@cloudflare.com> Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. ]] -- Simple parsing example of UDP/DNS that counts frequency of QTYPEs. -- It shows how to parse packet variable-length packet structures. local ffi = require("ffi") local bpf = require("bpf") local S = require("syscall") -- Shared part of the program local map = assert(bpf.map('array', 256)) -- Kernel-space part of the program local prog = bpf.socket('lo', function (skb) local ip = pkt.ip -- Accept only UDP messages if ip.proto ~= c.ip.proto_udp then return false end local udp = ip.udp -- Only messages >12 octets (DNS header) if udp.length < 12 then return false end -- Unroll QNAME (up to 2 labels) udp = udp.data + 12 local label = udp[0] if label > 0 then udp = udp + label + 1 label = udp[0] if label > 0 then udp = udp + label + 1 end end -- Track QTYPE (low types) if udp[0] == 0 then local qtype = udp[2] -- Low octet from QTYPE xadd(map[qtype], 1) end end) -- User-space part of the program for _ = 1, 10 do for k,v in map.pairs,map,0 do v = tonumber(v) if v > 0 then print(string.format('TYPE%d: %d', k, v)) end end S.sleep(1) end