package dnsforward import ( "encoding/binary" "net" "strings" "time" "github.com/AdguardTeam/AdGuardHome/internal/dhcpd" "github.com/AdguardTeam/AdGuardHome/internal/filtering" "github.com/AdguardTeam/dnsproxy/proxy" "github.com/AdguardTeam/golibs/log" "github.com/AdguardTeam/golibs/netutil" "github.com/AdguardTeam/golibs/stringutil" "github.com/miekg/dns" ) // To transfer information between modules type dnsContext struct { proxyCtx *proxy.DNSContext // setts are the filtering settings for the client. setts *filtering.Settings result *filtering.Result // origResp is the response received from upstream. It is set when the // response is modified by filters. origResp *dns.Msg // unreversedReqIP stores an IP address obtained from PTR request if it // parsed successfully and belongs to one of locally-served IP ranges as per // RFC 6303. unreversedReqIP net.IP // err is the error returned from a processing function. err error // clientID is the clientID from DoH, DoQ, or DoT, if provided. clientID string // origQuestion is the question received from the client. It is set // when the request is modified by rewrites. origQuestion dns.Question // startTime is the time at which the processing of the request has started. startTime time.Time // protectionEnabled shows if the filtering is enabled, and if the // server's DNS filter is ready. protectionEnabled bool // responseFromUpstream shows if the response is received from the // upstream servers. responseFromUpstream bool // responseAD shows if the response had the AD bit set. responseAD bool // isLocalClient shows if client's IP address is from locally-served // network. isLocalClient bool } // resultCode is the result of a request processing function. type resultCode int const ( // resultCodeSuccess is returned when a handler performed successfully, // and the next handler must be called. resultCodeSuccess resultCode = iota // resultCodeFinish is returned when a handler performed successfully, // and the processing of the request must be stopped. resultCodeFinish // resultCodeError is returned when a handler failed, and the processing // of the request must be stopped. resultCodeError ) // handleDNSRequest filters the incoming DNS requests and writes them to the query log func (s *Server) handleDNSRequest(_ *proxy.Proxy, d *proxy.DNSContext) error { ctx := &dnsContext{ proxyCtx: d, result: &filtering.Result{}, startTime: time.Now(), } type modProcessFunc func(ctx *dnsContext) (rc resultCode) // Since (*dnsforward.Server).handleDNSRequest(...) is used as // proxy.(Config).RequestHandler, there is no need for additional index // out of range checking in any of the following functions, because the // (*proxy.Proxy).handleDNSRequest method performs it before calling the // appropriate handler. mods := []modProcessFunc{ s.processRecursion, s.processInitial, s.processDetermineLocal, s.processInternalHosts, s.processRestrictLocal, s.processInternalIPAddrs, s.processFilteringBeforeRequest, s.processLocalPTR, s.processUpstream, s.processFilteringAfterResponse, s.ipset.process, s.processQueryLogsAndStats, } for _, process := range mods { r := process(ctx) switch r { case resultCodeSuccess: // continue: call the next filter case resultCodeFinish: return nil case resultCodeError: return ctx.err } } if d.Res != nil { d.Res.Compress = true // some devices require DNS message compression } return nil } // processRecursion checks the incoming request and halts it's handling if s // have tried to resolve it recently. func (s *Server) processRecursion(dctx *dnsContext) (rc resultCode) { pctx := dctx.proxyCtx if msg := pctx.Req; msg != nil && s.recDetector.check(*msg) { log.Debug("recursion detected resolving %q", msg.Question[0].Name) pctx.Res = s.genNXDomain(pctx.Req) return resultCodeFinish } return resultCodeSuccess } // processInitial terminates the following processing for some requests if // needed and enriches the ctx with some client-specific information. // // TODO(e.burkov): Decompose into less general processors. func (s *Server) processInitial(ctx *dnsContext) (rc resultCode) { d := ctx.proxyCtx if s.conf.AAAADisabled && d.Req.Question[0].Qtype == dns.TypeAAAA { _ = proxy.CheckDisabledAAAARequest(d, true) return resultCodeFinish } if s.conf.OnDNSRequest != nil { s.conf.OnDNSRequest(d) } // disable Mozilla DoH // https://support.mozilla.org/en-US/kb/canary-domain-use-application-dnsnet if (d.Req.Question[0].Qtype == dns.TypeA || d.Req.Question[0].Qtype == dns.TypeAAAA) && d.Req.Question[0].Name == "use-application-dns.net." { d.Res = s.genNXDomain(d.Req) return resultCodeFinish } // Get the client's ID if any. It should be performed before getting // client-specific filtering settings. var key [8]byte binary.BigEndian.PutUint64(key[:], d.RequestID) ctx.clientID = string(s.clientIDCache.Get(key[:])) // Get the client-specific filtering settings. ctx.protectionEnabled = s.conf.ProtectionEnabled ctx.setts = s.getClientRequestFilteringSettings(ctx) return resultCodeSuccess } func (s *Server) setTableHostToIP(t hostToIPTable) { s.tableHostToIPLock.Lock() defer s.tableHostToIPLock.Unlock() s.tableHostToIP = t } func (s *Server) setTableIPToHost(t *netutil.IPMap) { s.tableIPToHostLock.Lock() defer s.tableIPToHostLock.Unlock() s.tableIPToHost = t } func (s *Server) onDHCPLeaseChanged(flags int) { var err error add := true switch flags { case dhcpd.LeaseChangedAdded, dhcpd.LeaseChangedAddedStatic, dhcpd.LeaseChangedRemovedStatic: // Go on. case dhcpd.LeaseChangedRemovedAll: add = false default: return } var hostToIP hostToIPTable var ipToHost *netutil.IPMap if add { ll := s.dhcpServer.Leases(dhcpd.LeasesAll) hostToIP = make(hostToIPTable, len(ll)) ipToHost = netutil.NewIPMap(len(ll)) for _, l := range ll { // TODO(a.garipov): Remove this after we're finished with the client // hostname validations in the DHCP server code. err = netutil.ValidateDomainName(l.Hostname) if err != nil { log.Debug( "dns: skipping invalid hostname %q from dhcp: %s", l.Hostname, err, ) } lowhost := strings.ToLower(l.Hostname) ipToHost.Set(l.IP, lowhost) ip := make(net.IP, 4) copy(ip, l.IP.To4()) hostToIP[lowhost] = ip } log.Debug("dns: added %d A/PTR entries from DHCP", ipToHost.Len()) } s.setTableHostToIP(hostToIP) s.setTableIPToHost(ipToHost) } // processDetermineLocal determines if the client's IP address is from // locally-served network and saves the result into the context. func (s *Server) processDetermineLocal(dctx *dnsContext) (rc resultCode) { rc = resultCodeSuccess var ip net.IP if ip, _ = netutil.IPAndPortFromAddr(dctx.proxyCtx.Addr); ip == nil { return rc } dctx.isLocalClient = s.subnetDetector.IsLocallyServedNetwork(ip) return rc } // hostToIP tries to get an IP leased by DHCP and returns the copy of address // since the data inside the internal table may be changed while request // processing. It's safe for concurrent use. func (s *Server) hostToIP(host string) (ip net.IP, ok bool) { s.tableHostToIPLock.Lock() defer s.tableHostToIPLock.Unlock() if s.tableHostToIP == nil { return nil, false } var ipFromTable net.IP ipFromTable, ok = s.tableHostToIP[host] if !ok { return nil, false } ip = make(net.IP, len(ipFromTable)) copy(ip, ipFromTable) return ip, true } // processInternalHosts respond to A requests if the target hostname is known to // the server. // // TODO(a.garipov): Adapt to AAAA as well. func (s *Server) processInternalHosts(dctx *dnsContext) (rc resultCode) { if !s.dhcpServer.Enabled() { return resultCodeSuccess } req := dctx.proxyCtx.Req q := req.Question[0] // Go on processing the AAAA request despite the fact that we don't support // it yet. The expected behavior here is to respond with an empty answer // and not NXDOMAIN. if q.Qtype != dns.TypeA && q.Qtype != dns.TypeAAAA { return resultCodeSuccess } reqHost := strings.ToLower(q.Name) // TODO(a.garipov): Move everything related to DHCP local domain to the DHCP // server. host := strings.TrimSuffix(reqHost, s.localDomainSuffix) if host == reqHost { return resultCodeSuccess } d := dctx.proxyCtx if !dctx.isLocalClient { log.Debug("dns: %q requests for internal host", d.Addr) d.Res = s.genNXDomain(req) // Do not even put into query log. return resultCodeFinish } ip, ok := s.hostToIP(host) if !ok { // TODO(e.burkov): Inspect special cases when user want to apply some // rules handled by other processors to the hosts with TLD. d.Res = s.genNXDomain(req) return resultCodeFinish } log.Debug("dns: internal record: %s -> %s", q.Name, ip) resp := s.makeResponse(req) if q.Qtype == dns.TypeA { a := &dns.A{ Hdr: s.hdr(req, dns.TypeA), A: ip, } resp.Answer = append(resp.Answer, a) } dctx.proxyCtx.Res = resp return resultCodeSuccess } // processRestrictLocal responds with NXDOMAIN to PTR requests for IP addresses // in locally-served network from external clients. func (s *Server) processRestrictLocal(ctx *dnsContext) (rc resultCode) { d := ctx.proxyCtx req := d.Req q := req.Question[0] if q.Qtype != dns.TypePTR { // No need for restriction. return resultCodeSuccess } ip, err := netutil.IPFromReversedAddr(q.Name) if err != nil { log.Debug("dns: parsing reversed addr: %s", err) // DNS-Based Service Discovery uses PTR records having not an ARPA // format of the domain name in question. Those shouldn't be // invalidated. See http://www.dns-sd.org/ServerStaticSetup.html and // RFC 2782. name := strings.TrimSuffix(q.Name, ".") if err = netutil.ValidateSRVDomainName(name); err != nil { log.Debug("dns: validating service domain: %s", err) return resultCodeError } log.Debug("dns: request is for a service domain") return resultCodeSuccess } // Restrict an access to local addresses for external clients. We also // assume that all the DHCP leases we give are locally-served or at least // don't need to be inaccessible externally. if !s.subnetDetector.IsLocallyServedNetwork(ip) { log.Debug("dns: addr %s is not from locally-served network", ip) return resultCodeSuccess } if !ctx.isLocalClient { log.Debug("dns: %q requests an internal ip", d.Addr) d.Res = s.genNXDomain(req) // Do not even put into query log. return resultCodeFinish } // Do not perform unreversing ever again. ctx.unreversedReqIP = ip // There is no need to filter request from external addresses since this // code is only executed when the request is for locally-served ARPA // hostname so disable redundant filters. ctx.setts.ParentalEnabled = false ctx.setts.SafeBrowsingEnabled = false ctx.setts.SafeSearchEnabled = false ctx.setts.ServicesRules = nil // Nothing to restrict. return resultCodeSuccess } // ipToHost tries to get a hostname leased by DHCP. It's safe for concurrent // use. func (s *Server) ipToHost(ip net.IP) (host string, ok bool) { s.tableIPToHostLock.Lock() defer s.tableIPToHostLock.Unlock() if s.tableIPToHost == nil { return "", false } var v interface{} v, ok = s.tableIPToHost.Get(ip) if !ok { return "", false } if host, ok = v.(string); !ok { log.Error("dns: bad type %T in tableIPToHost for %s", v, ip) return "", false } return host, true } // Respond to PTR requests if the target IP is leased by our DHCP server and the // requestor is inside the local network. func (s *Server) processInternalIPAddrs(ctx *dnsContext) (rc resultCode) { d := ctx.proxyCtx if d.Res != nil { return resultCodeSuccess } ip := ctx.unreversedReqIP if ip == nil { return resultCodeSuccess } host, ok := s.ipToHost(ip) if !ok { return resultCodeSuccess } log.Debug("dns: reverse-lookup: %s -> %s", ip, host) req := d.Req resp := s.makeResponse(req) ptr := &dns.PTR{ Hdr: dns.RR_Header{ Name: req.Question[0].Name, Rrtype: dns.TypePTR, Ttl: s.conf.BlockedResponseTTL, Class: dns.ClassINET, }, Ptr: dns.Fqdn(host), } resp.Answer = append(resp.Answer, ptr) d.Res = resp return resultCodeSuccess } // processLocalPTR responds to PTR requests if the target IP is detected to be // inside the local network and the query was not answered from DHCP. func (s *Server) processLocalPTR(ctx *dnsContext) (rc resultCode) { d := ctx.proxyCtx if d.Res != nil { return resultCodeSuccess } ip := ctx.unreversedReqIP if ip == nil { return resultCodeSuccess } s.serverLock.RLock() defer s.serverLock.RUnlock() if !s.subnetDetector.IsLocallyServedNetwork(ip) { return resultCodeSuccess } if s.conf.UsePrivateRDNS { s.recDetector.add(*d.Req) if err := s.localResolvers.Resolve(d); err != nil { ctx.err = err return resultCodeError } } if d.Res == nil { d.Res = s.genNXDomain(d.Req) // Do not even put into query log. return resultCodeFinish } return resultCodeSuccess } // Apply filtering logic func (s *Server) processFilteringBeforeRequest(ctx *dnsContext) (rc resultCode) { if ctx.proxyCtx.Res != nil { // Go on since the response is already set. return resultCodeSuccess } s.serverLock.RLock() defer s.serverLock.RUnlock() if s.dnsFilter == nil { return resultCodeSuccess } var err error if ctx.result, err = s.filterDNSRequest(ctx); err != nil { ctx.err = err return resultCodeError } return resultCodeSuccess } // ipStringFromAddr extracts an IP address string from net.Addr. func ipStringFromAddr(addr net.Addr) (ipStr string) { if ip, _ := netutil.IPAndPortFromAddr(addr); ip != nil { return ip.String() } return "" } // processUpstream passes request to upstream servers and handles the response. func (s *Server) processUpstream(dctx *dnsContext) (rc resultCode) { pctx := dctx.proxyCtx if pctx.Res != nil { // The response has already been set. return resultCodeSuccess } if pctx.Addr != nil && s.conf.GetCustomUpstreamByClient != nil { // Use the clientID first, since it has a higher priority. id := stringutil.Coalesce(dctx.clientID, ipStringFromAddr(pctx.Addr)) upsConf, err := s.conf.GetCustomUpstreamByClient(id) if err != nil { log.Error("dns: getting custom upstreams for client %s: %s", id, err) } else if upsConf != nil { log.Debug("dns: using custom upstreams for client %s", id) pctx.CustomUpstreamConfig = upsConf } } req := pctx.Req origReqAD := false if s.conf.EnableDNSSEC { if req.AuthenticatedData { origReqAD = true } else { req.AuthenticatedData = true } } // Process the request further since it wasn't filtered. prx := s.proxy() if prx == nil { dctx.err = srvClosedErr return resultCodeError } if dctx.err = prx.Resolve(pctx); dctx.err != nil { return resultCodeError } dctx.responseFromUpstream = true dctx.responseAD = pctx.Res.AuthenticatedData if s.conf.EnableDNSSEC && !origReqAD { pctx.Req.AuthenticatedData = false pctx.Res.AuthenticatedData = false } return resultCodeSuccess } // Apply filtering logic after we have received response from upstream servers func (s *Server) processFilteringAfterResponse(ctx *dnsContext) (rc resultCode) { d := ctx.proxyCtx switch res := ctx.result; res.Reason { case filtering.NotFilteredAllowList: // Go on. case filtering.Rewritten, filtering.RewrittenRule: if len(ctx.origQuestion.Name) == 0 { // origQuestion is set in case we get only CNAME without IP from // rewrites table. break } d.Req.Question[0], d.Res.Question[0] = ctx.origQuestion, ctx.origQuestion if len(d.Res.Answer) > 0 { answer := append([]dns.RR{s.genAnswerCNAME(d.Req, res.CanonName)}, d.Res.Answer...) d.Res.Answer = answer } default: // Check the response only if the it's from an upstream. Don't check // the response if the protection is disabled since dnsrewrite rules // aren't applied to it anyway. if !ctx.protectionEnabled || !ctx.responseFromUpstream || s.dnsFilter == nil { break } origResp := d.Res result, err := s.filterDNSResponse(ctx) if err != nil { ctx.err = err return resultCodeError } if result != nil { ctx.result = result ctx.origResp = origResp } } if ctx.result == nil { ctx.result = &filtering.Result{} } return resultCodeSuccess }