--- Library for supporting DNS Service Discovery -- -- The library supports -- * Unicast and Multicast requests -- * Decoding responses -- * Running requests in parallel using Lua coroutines -- -- The library contains the following classes -- * Comm -- ** A class with static functions that handle communication using the dns library -- * Helper -- ** The helper class wraps the Comm class using functions with a more descriptive name. -- ** The purpose of this class is to give developers easy access to some of the common DNS-SD tasks. -- * Util -- ** The Util class contains a number of static functions mainly used to convert data. -- -- The following code snippet queries all mDNS resolvers on the network for a -- full list of their supported services and returns the formatted output: -- -- local helper = dnssd.Helper:new( ) -- helper:setMulticast(true) -- return stdnse.format_output(helper:queryServices()) -- -- -- This next snippet queries a specific host for the same information: -- -- local helper = dnssd.Helper:new( host, port ) -- return stdnse.format_output(helper:queryServices()) -- -- -- In order to query for a specific service a string or table with service -- names can be passed to the Helper.queryServices method. -- -- @args dnssd.services string or table containing services to query -- -- @author Patrik Karlsson -- @copyright Same as Nmap--See https://nmap.org/book/man-legal.html -- local coroutine = require "coroutine" local dns = require "dns" local ipOps = require "ipOps" local nmap = require "nmap" local stdnse = require "stdnse" local string = require "string" local table = require "table" local target = require "target" _ENV = stdnse.module("dnssd", stdnse.seeall) Util = { --- Compare function used for sorting IP-addresses -- -- @param a table containing first item -- @param b table containing second item -- @return true if a is less than b ipCompare = function(a, b) return ipOps.compare_ip(a, "lt", b) end, --- Function used to compare discovered DNS services so they can be sorted -- -- @param a table containing first item -- @param b table containing second item -- @return true if the port of a is less than the port of b serviceCompare = function(a, b) -- if no port is found use 999999 for comparing, this way all services -- without ports and device information gets printed at the end local port_a = a.name:match("^(%d+)") or 999999 local port_b = b.name:match("^(%d+)") or 999999 if ( tonumber(port_a) < tonumber(port_b) ) then return true end return false end, --- Creates a service host table -- -- ['_ftp._tcp.local'] = {10.10.10.10,20.20.20.20} -- ['_http._tcp.local'] = {30.30.30.30,40.40.40.40} -- -- @param response containing multiple responses from dns.query -- @return services table containing the service name as a key and all host addresses as value createSvcHostTbl = function( response ) local services = {} -- Create unique table of services for _, r in ipairs( response ) do -- do we really have multiple responses? if ( not(r.output) ) then return end for _, svc in ipairs(r.output ) do services[svc] = services[svc] or {} table.insert(services[svc], r.peer) end end return services end, --- Creates a unique list of services -- -- @param response containing a single or multiple responses from -- dns.query -- @return array of strings containing service names getUniqueServices = function( response ) local services = {} for _, r in ipairs(response) do if ( r.output ) then for _, svc in ipairs(r.output) do services[svc] = true end else services[r] = true end end return services end, --- Returns the amount of currently active threads -- -- @param threads table containing the list of threads -- @return count number containing the number of non-dead threads threadCount = function( threads ) local count = 0 for thread in pairs(threads) do if ( coroutine.status(thread) == "dead" ) then threads[thread] = nil else count = count + 1 end end return count end } Comm = { --- Gets a record from both the Answer and Additional section -- -- @param dtype DNS resource record type. -- @param response Decoded DNS response. -- @param retAll If true, return all entries, not just the first. -- @return True if one or more answers of the required type were found - otherwise false. -- @return Answer according to the answer fetcher for dtype or an Error message. getRecordType = function( dtype, response, retAll ) local result = {} local status1, answers = dns.findNiceAnswer( dtype, response, retAll ) if status1 then if retAll then for _, v in ipairs(answers) do table.insert(result, string.format("%s", v) ) end else return true, answers end end local status2, answers = dns.findNiceAdditional( dtype, response, retAll ) if status2 then if retAll then for _, v in ipairs(answers) do table.insert(result, v) end else return true, answers end end if not status1 and not status2 then return false, answers end return true, result end, --- Send a query for a particular service and store the response in a table -- -- @param host string containing the ip to connect to -- @param port number containing the port to connect to -- @param svc the service record to retrieve -- @param multiple true if responses from multiple hosts are expected -- @param svcresponse table to which results are stored queryService = function( host, port, svc, multiple, svcresponse ) local condvar = nmap.condvar(svcresponse) local status, response = dns.query( svc, { port = port, host = host, dtype="PTR", retPkt=true, retAll=true, multiple=multiple, sendCount=1, timeout=2000} ) if not status then stdnse.debug1("Failed to query service: %s; Error: %s", svc, response) return end svcresponse[svc] = svcresponse[svc] or {} if ( multiple ) then for _, r in ipairs(response) do table.insert( svcresponse[svc], r ) end else svcresponse[svc] = response end condvar("broadcast") end, --- Decodes a record received from the queryService function -- -- @param response as returned by queryService -- @param result table into which the decoded output should be stored decodeRecords = function( response, result ) local service, deviceinfo = {}, {} local txt = {} local ipv6, srv, address, port, proto local record = ( #response.questions > 0 and response.questions[1].dname ) and response.questions[1].dname or "" local status, ip = Comm.getRecordType( dns.types.A, response, false ) if status then address = ip end status, ipv6 = Comm.getRecordType( dns.types.AAAA, response, false ) if status then address = address or "" address = address .. " " .. ipv6 end status, txt = Comm.getRecordType( dns.types.TXT, response, true ) if status then for _, v in ipairs(txt) do if v:len() > 0 then table.insert(service, v) end end end status, srv = Comm.getRecordType( dns.types.SRV, response, false ) if status then local srvparams = stdnse.strsplit( ":", srv ) if #srvparams > 3 then port = srvparams[3] end end if address then table.insert( service, ("Address=%s"):format( address ) ) end if record == "_device-info._tcp.local" then service.name = "Device Information" deviceinfo = service table.insert(result, deviceinfo) else local serviceparams = stdnse.strsplit("[.]", record) if #serviceparams > 2 then local servicename = serviceparams[1]:sub(2) local proto = serviceparams[2]:sub(2) if port == nil or proto == nil or servicename == nil then service.name = record else service.name = string.format( "%s/%s %s", port, proto, servicename) end end table.insert( result, service ) end end, --- Query the mDNS resolvers for a list of their services -- -- @param host table as received by the action function -- @param port number specifying the port to connect to -- @param multiple receive multiple responses (multicast) -- @return True if a dns response was received and contained an answer of -- the requested type, or the decoded dns response was requested -- (retPkt) and is being returned - or False otherwise. -- @return String answer of the requested type, Table of answers or a -- String error message of one of the following: -- "No Such Name", "No Servers", "No Answers", -- "Unable to handle response" queryAllServices = function( host, port, multiple ) local sendCount, timeout = 1, 2000 if ( multiple ) then sendCount, timeout = 2, 5000 end return dns.query( "_services._dns-sd._udp.local", { port = port, host = ( host.ip or host ), dtype="PTR", retAll=true, multiple=multiple, sendCount=sendCount, timeout=timeout } ) end, } Helper = { --- Creates a new helper instance -- -- @param host string containing the host name or ip -- @param port number containing the port to connect to -- @return o a new instance of Helper new = function( self, host, port ) local o = {} setmetatable(o, self) self.__index = self o.host = host o.port = port o.mcast = false return o end, --- Instructs the helper to use unconnected sockets supporting multicast -- -- @param mcast boolean true if multicast is to be used, false otherwise setMulticast = function( self, mcast ) assert( type(mcast)=="boolean", "mcast has to be either true or false") self.mcast = mcast end, --- Performs a DNS-SD query against a host -- -- @param host table as received by the action function -- @param port number specifying the port to connect to -- @param service string or table with the service(s) to query eg. -- _ssh._tcp.local, _afpovertcp._tcp.local -- if nil defaults to _services._dns-sd._udp.local (all) -- @param mcast boolean true if a multicast query is to be done -- @return status true on success, false on failure -- @return response table suitable for stdnse.format_output queryServices = function( self, service ) local result = {} local status, response local mcast = self.mcast local port = self.port or 5353 local family = nmap.address_family() local host = mcast and (family=="inet6" and "ff02::fb" or "224.0.0.251") or self.host local service = service or stdnse.get_script_args('dnssd.services') if ( not(service) ) then status, response = Comm.queryAllServices( host, port, mcast ) if ( not(status) ) then return status, response end else if ( 'string' == type(service) ) then response = { service } elseif ( 'table' == type(service) ) then response = service end end response = Util.getUniqueServices(response) local svcresponse = {} local condvar = nmap.condvar( svcresponse ) local threads = {} for svc in pairs(response) do local co = stdnse.new_thread( Comm.queryService, (host.ip or host), port, svc, mcast, svcresponse ) threads[co] = true end -- Wait for all threads to finish running while Util.threadCount(threads)>0 do condvar("wait") end local ipsvctbl = {} if ( mcast ) then -- Process all records that were returned for svcname, response in pairs(svcresponse) do for _, r in ipairs( response ) do ipsvctbl[r.peer] = ipsvctbl[r.peer] or {} Comm.decodeRecords( r.output, ipsvctbl[r.peer] ) end end else -- Process all records that were returned for svcname, response in pairs(svcresponse) do Comm.decodeRecords( response, result ) end end if ( mcast ) then -- Restructure and build our output table for ip, svctbl in pairs( ipsvctbl ) do table.sort(svctbl, Util.serviceCompare) svctbl.name = ip if target.ALLOW_NEW_TARGETS then target.add(ip) end table.insert( result, svctbl ) end table.sort( result, Util.ipCompare ) else -- sort the tables per port table.sort( result, Util.serviceCompare ) end return true, result end, } return _ENV;