AdGuardHome/dnsforward/dnsforward.go

893 lines
26 KiB
Go

package dnsforward
import (
"crypto/tls"
"fmt"
"net"
"net/http"
"runtime"
"strings"
"sync"
"time"
"github.com/AdguardTeam/AdGuardHome/dnsfilter"
"github.com/AdguardTeam/AdGuardHome/querylog"
"github.com/AdguardTeam/AdGuardHome/stats"
"github.com/AdguardTeam/dnsproxy/proxy"
"github.com/AdguardTeam/dnsproxy/upstream"
"github.com/AdguardTeam/golibs/log"
"github.com/joomcode/errorx"
"github.com/miekg/dns"
)
// DefaultTimeout is the default upstream timeout
const DefaultTimeout = 10 * time.Second
const (
safeBrowsingBlockHost = "standard-block.dns.adguard.com"
parentalBlockHost = "family-block.dns.adguard.com"
)
var defaultDNS = []string{
"https://dns.quad9.net/dns-query",
}
var defaultBootstrap = []string{"9.9.9.9", "149.112.112.112"}
// Server is the main way to start a DNS server.
//
// Example:
// s := dnsforward.Server{}
// err := s.Start(nil) // will start a DNS server listening on default port 53, in a goroutine
// err := s.Reconfigure(ServerConfig{UDPListenAddr: &net.UDPAddr{Port: 53535}}) // will reconfigure running DNS server to listen on UDP port 53535
// err := s.Stop() // will stop listening on port 53535 and cancel all goroutines
// err := s.Start(nil) // will start listening again, on port 53535, in a goroutine
//
// The zero Server is empty and ready for use.
type Server struct {
dnsProxy *proxy.Proxy // DNS proxy instance
dnsFilter *dnsfilter.Dnsfilter // DNS filter instance
queryLog querylog.QueryLog // Query log instance
stats stats.Stats
access *accessCtx
// DNS proxy instance for internal usage
// We don't Start() it and so no listen port is required.
internalProxy *proxy.Proxy
webRegistered bool
isRunning bool
sync.RWMutex
conf ServerConfig
}
// NewServer creates a new instance of the dnsforward.Server
// Note: this function must be called only once
func NewServer(dnsFilter *dnsfilter.Dnsfilter, stats stats.Stats, queryLog querylog.QueryLog) *Server {
s := &Server{}
s.dnsFilter = dnsFilter
s.stats = stats
s.queryLog = queryLog
if runtime.GOARCH == "mips" || runtime.GOARCH == "mipsle" {
// Use plain DNS on MIPS, encryption is too slow
defaultDNS = defaultBootstrap
}
return s
}
// Close - close object
func (s *Server) Close() {
s.Lock()
s.dnsFilter = nil
s.stats = nil
s.queryLog = nil
s.dnsProxy = nil
s.Unlock()
}
func stringArrayDup(a []string) []string {
a2 := make([]string, len(a))
copy(a2, a)
return a2
}
// WriteDiskConfig - write configuration
func (s *Server) WriteDiskConfig(c *FilteringConfig) {
s.RLock()
sc := s.conf.FilteringConfig
*c = sc
c.RatelimitWhitelist = stringArrayDup(sc.RatelimitWhitelist)
c.BootstrapDNS = stringArrayDup(sc.BootstrapDNS)
c.AllowedClients = stringArrayDup(sc.AllowedClients)
c.DisallowedClients = stringArrayDup(sc.DisallowedClients)
c.BlockedHosts = stringArrayDup(sc.BlockedHosts)
c.UpstreamDNS = stringArrayDup(sc.UpstreamDNS)
s.RUnlock()
}
// FilteringConfig represents the DNS filtering configuration of AdGuard Home
// The zero FilteringConfig is empty and ready for use.
type FilteringConfig struct {
// Filtering callback function
FilterHandler func(clientAddr string, settings *dnsfilter.RequestFilteringSettings) `yaml:"-"`
// This callback function returns the list of upstream servers for a client specified by IP address
GetUpstreamsByClient func(clientAddr string) []upstream.Upstream `yaml:"-"`
ProtectionEnabled bool `yaml:"protection_enabled"` // whether or not use any of dnsfilter features
BlockingMode string `yaml:"blocking_mode"` // mode how to answer filtered requests
BlockingIPv4 string `yaml:"blocking_ipv4"` // IP address to be returned for a blocked A request
BlockingIPv6 string `yaml:"blocking_ipv6"` // IP address to be returned for a blocked AAAA request
BlockingIPAddrv4 net.IP `yaml:"-"`
BlockingIPAddrv6 net.IP `yaml:"-"`
BlockedResponseTTL uint32 `yaml:"blocked_response_ttl"` // if 0, then default is used (3600)
Ratelimit uint32 `yaml:"ratelimit"` // max number of requests per second from a given IP (0 to disable)
RatelimitWhitelist []string `yaml:"ratelimit_whitelist"` // a list of whitelisted client IP addresses
RefuseAny bool `yaml:"refuse_any"` // if true, refuse ANY requests
BootstrapDNS []string `yaml:"bootstrap_dns"` // a list of bootstrap DNS for DoH and DoT (plain DNS only)
AllServers bool `yaml:"all_servers"` // if true, parallel queries to all configured upstream servers are enabled
EnableEDNSClientSubnet bool `yaml:"edns_client_subnet"` // Enable EDNS Client Subnet option
AllowedClients []string `yaml:"allowed_clients"` // IP addresses of whitelist clients
DisallowedClients []string `yaml:"disallowed_clients"` // IP addresses of clients that should be blocked
BlockedHosts []string `yaml:"blocked_hosts"` // hosts that should be blocked
// IP (or domain name) which is used to respond to DNS requests blocked by parental control or safe-browsing
ParentalBlockHost string `yaml:"parental_block_host"`
SafeBrowsingBlockHost string `yaml:"safebrowsing_block_host"`
CacheSize uint `yaml:"cache_size"` // DNS cache size (in bytes)
UpstreamDNS []string `yaml:"upstream_dns"`
}
// TLSConfig is the TLS configuration for HTTPS, DNS-over-HTTPS, and DNS-over-TLS
type TLSConfig struct {
TLSListenAddr *net.TCPAddr `yaml:"-" json:"-"`
CertificateChain string `yaml:"certificate_chain" json:"certificate_chain"` // PEM-encoded certificates chain
PrivateKey string `yaml:"private_key" json:"private_key"` // PEM-encoded private key
CertificatePath string `yaml:"certificate_path" json:"certificate_path"` // certificate file name
PrivateKeyPath string `yaml:"private_key_path" json:"private_key_path"` // private key file name
CertificateChainData []byte `yaml:"-" json:"-"`
PrivateKeyData []byte `yaml:"-" json:"-"`
}
// ServerConfig represents server configuration.
// The zero ServerConfig is empty and ready for use.
type ServerConfig struct {
UDPListenAddr *net.UDPAddr // UDP listen address
TCPListenAddr *net.TCPAddr // TCP listen address
Upstreams []upstream.Upstream // Configured upstreams
DomainsReservedUpstreams map[string][]upstream.Upstream // Map of domains and lists of configured upstreams
OnDNSRequest func(d *proxy.DNSContext)
FilteringConfig
TLSConfig
// Called when the configuration is changed by HTTP request
ConfigModified func()
// Register an HTTP handler
HTTPRegister func(string, string, func(http.ResponseWriter, *http.Request))
}
// if any of ServerConfig values are zero, then default values from below are used
var defaultValues = ServerConfig{
UDPListenAddr: &net.UDPAddr{Port: 53},
TCPListenAddr: &net.TCPAddr{Port: 53},
FilteringConfig: FilteringConfig{BlockedResponseTTL: 3600},
}
// Resolve - get IP addresses by host name from an upstream server.
// No request/response filtering is performed.
// Query log and Stats are not updated.
// This method may be called before Start().
func (s *Server) Resolve(host string) ([]net.IPAddr, error) {
s.RLock()
defer s.RUnlock()
return s.internalProxy.LookupIPAddr(host)
}
// Exchange - send DNS request to an upstream server and receive response
// No request/response filtering is performed.
// Query log and Stats are not updated.
// This method may be called before Start().
func (s *Server) Exchange(req *dns.Msg) (*dns.Msg, error) {
s.RLock()
defer s.RUnlock()
ctx := &proxy.DNSContext{
Proto: "udp",
Req: req,
StartTime: time.Now(),
}
err := s.internalProxy.Resolve(ctx)
if err != nil {
return nil, err
}
return ctx.Res, nil
}
// Start starts the DNS server
func (s *Server) Start() error {
s.Lock()
defer s.Unlock()
return s.startInternal()
}
// startInternal starts without locking
func (s *Server) startInternal() error {
err := s.dnsProxy.Start()
if err == nil {
s.isRunning = true
}
return err
}
// Prepare the object
func (s *Server) Prepare(config *ServerConfig) error {
if config != nil {
s.conf = *config
if s.conf.BlockingMode == "custom_ip" {
s.conf.BlockingIPAddrv4 = net.ParseIP(s.conf.BlockingIPv4)
s.conf.BlockingIPAddrv6 = net.ParseIP(s.conf.BlockingIPv6)
if s.conf.BlockingIPAddrv4 == nil || s.conf.BlockingIPAddrv6 == nil {
return fmt.Errorf("DNS: invalid custom blocking IP address specified")
}
}
}
if len(s.conf.UpstreamDNS) == 0 {
s.conf.UpstreamDNS = defaultDNS
}
if len(s.conf.BootstrapDNS) == 0 {
s.conf.BootstrapDNS = defaultBootstrap
}
upstreamConfig, err := proxy.ParseUpstreamsConfig(s.conf.UpstreamDNS, s.conf.BootstrapDNS, DefaultTimeout)
if err != nil {
return fmt.Errorf("DNS: proxy.ParseUpstreamsConfig: %s", err)
}
s.conf.Upstreams = upstreamConfig.Upstreams
s.conf.DomainsReservedUpstreams = upstreamConfig.DomainReservedUpstreams
if len(s.conf.ParentalBlockHost) == 0 {
s.conf.ParentalBlockHost = parentalBlockHost
}
if len(s.conf.SafeBrowsingBlockHost) == 0 {
s.conf.SafeBrowsingBlockHost = safeBrowsingBlockHost
}
if s.conf.UDPListenAddr == nil {
s.conf.UDPListenAddr = defaultValues.UDPListenAddr
}
if s.conf.TCPListenAddr == nil {
s.conf.TCPListenAddr = defaultValues.TCPListenAddr
}
proxyConfig := proxy.Config{
UDPListenAddr: s.conf.UDPListenAddr,
TCPListenAddr: s.conf.TCPListenAddr,
Ratelimit: int(s.conf.Ratelimit),
RatelimitWhitelist: s.conf.RatelimitWhitelist,
RefuseAny: s.conf.RefuseAny,
CacheEnabled: true,
CacheSizeBytes: int(s.conf.CacheSize),
Upstreams: s.conf.Upstreams,
DomainsReservedUpstreams: s.conf.DomainsReservedUpstreams,
BeforeRequestHandler: s.beforeRequestHandler,
RequestHandler: s.handleDNSRequest,
AllServers: s.conf.AllServers,
EnableEDNSClientSubnet: s.conf.EnableEDNSClientSubnet,
}
intlProxyConfig := proxy.Config{
CacheEnabled: true,
CacheSizeBytes: 4096,
Upstreams: s.conf.Upstreams,
DomainsReservedUpstreams: s.conf.DomainsReservedUpstreams,
}
s.internalProxy = &proxy.Proxy{Config: intlProxyConfig}
s.access = &accessCtx{}
err = s.access.Init(s.conf.AllowedClients, s.conf.DisallowedClients, s.conf.BlockedHosts)
if err != nil {
return err
}
if s.conf.TLSListenAddr != nil && len(s.conf.CertificateChainData) != 0 && len(s.conf.PrivateKeyData) != 0 {
proxyConfig.TLSListenAddr = s.conf.TLSListenAddr
keypair, err := tls.X509KeyPair(s.conf.CertificateChainData, s.conf.PrivateKeyData)
if err != nil {
return errorx.Decorate(err, "Failed to parse TLS keypair")
}
proxyConfig.TLSConfig = &tls.Config{
Certificates: []tls.Certificate{keypair},
MinVersion: tls.VersionTLS12,
}
}
if len(proxyConfig.Upstreams) == 0 {
log.Fatal("len(proxyConfig.Upstreams) == 0")
}
if !s.webRegistered && s.conf.HTTPRegister != nil {
s.webRegistered = true
s.registerHandlers()
}
// Initialize and start the DNS proxy
s.dnsProxy = &proxy.Proxy{Config: proxyConfig}
return nil
}
// Stop stops the DNS server
func (s *Server) Stop() error {
s.Lock()
defer s.Unlock()
return s.stopInternal()
}
// stopInternal stops without locking
func (s *Server) stopInternal() error {
if s.dnsProxy != nil {
err := s.dnsProxy.Stop()
if err != nil {
return errorx.Decorate(err, "could not stop the DNS server properly")
}
}
s.isRunning = false
return nil
}
// IsRunning returns true if the DNS server is running
func (s *Server) IsRunning() bool {
s.RLock()
defer s.RUnlock()
return s.isRunning
}
// Reconfigure applies the new configuration to the DNS server
func (s *Server) Reconfigure(config *ServerConfig) error {
s.Lock()
defer s.Unlock()
log.Print("Start reconfiguring the server")
err := s.stopInternal()
if err != nil {
return errorx.Decorate(err, "could not reconfigure the server")
}
// It seems that net.Listener.Close() doesn't close file descriptors right away.
// We wait for some time and hope that this fd will be closed.
time.Sleep(100 * time.Millisecond)
err = s.Prepare(config)
if err != nil {
return errorx.Decorate(err, "could not reconfigure the server")
}
err = s.startInternal()
if err != nil {
return errorx.Decorate(err, "could not reconfigure the server")
}
return nil
}
// ServeHTTP is a HTTP handler method we use to provide DNS-over-HTTPS
func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
s.RLock()
p := s.dnsProxy
s.RUnlock()
if p != nil { // an attempt to protect against race in case we're here after Close() was called
p.ServeHTTP(w, r)
}
}
// Get IP address from net.Addr object
// Note: we can't use net.SplitHostPort(a.String()) because of IPv6 zone:
// https://github.com/AdguardTeam/AdGuardHome/issues/1261
func ipFromAddr(a net.Addr) string {
switch addr := a.(type) {
case *net.UDPAddr:
return addr.IP.String()
case *net.TCPAddr:
return addr.IP.String()
}
return ""
}
func (s *Server) beforeRequestHandler(p *proxy.Proxy, d *proxy.DNSContext) (bool, error) {
ip := ipFromAddr(d.Addr)
if s.access.IsBlockedIP(ip) {
log.Tracef("Client IP %s is blocked by settings", ip)
return false, nil
}
if len(d.Req.Question) == 1 {
host := strings.TrimSuffix(d.Req.Question[0].Name, ".")
if s.access.IsBlockedDomain(host) {
log.Tracef("Domain %s is blocked by settings", host)
return false, nil
}
}
return true, nil
}
// handleDNSRequest filters the incoming DNS requests and writes them to the query log
// nolint (gocyclo)
func (s *Server) handleDNSRequest(p *proxy.Proxy, d *proxy.DNSContext) error {
start := time.Now()
if s.conf.OnDNSRequest != nil {
s.conf.OnDNSRequest(d)
}
// disable Mozilla DoH
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 nil
}
// use dnsfilter before cache -- changed settings or filters would require cache invalidation otherwise
s.RLock()
// Synchronize access to s.dnsFilter so it won't be suddenly uninitialized while in use.
// This could happen after proxy server has been stopped, but its workers are not yet exited.
//
// A better approach is for proxy.Stop() to wait until all its workers exit,
// but this would require the Upstream interface to have Close() function
// (to prevent from hanging while waiting for unresponsive DNS server to respond).
var setts *dnsfilter.RequestFilteringSettings
var err error
res := &dnsfilter.Result{}
protectionEnabled := s.conf.ProtectionEnabled && s.dnsFilter != nil
if protectionEnabled {
setts = s.getClientRequestFilteringSettings(d)
res, err = s.filterDNSRequest(d, setts)
}
s.RUnlock()
if err != nil {
return err
}
var origResp *dns.Msg
if d.Res == nil {
answer := []dns.RR{}
originalQuestion := d.Req.Question[0]
if res.Reason == dnsfilter.ReasonRewrite && len(res.CanonName) != 0 {
answer = append(answer, s.genCNAMEAnswer(d.Req, res.CanonName))
// resolve canonical name, not the original host name
d.Req.Question[0].Name = dns.Fqdn(res.CanonName)
}
if d.Addr != nil && s.conf.GetUpstreamsByClient != nil {
clientIP := ipFromAddr(d.Addr)
upstreams := s.conf.GetUpstreamsByClient(clientIP)
if len(upstreams) > 0 {
log.Debug("Using custom upstreams for %s", clientIP)
d.Upstreams = upstreams
}
}
// request was not filtered so let it be processed further
err = p.Resolve(d)
if err != nil {
return err
}
if res.Reason == dnsfilter.ReasonRewrite && len(res.CanonName) != 0 {
d.Req.Question[0] = originalQuestion
d.Res.Question[0] = originalQuestion
if len(d.Res.Answer) != 0 {
answer = append(answer, d.Res.Answer...) // host -> IP
d.Res.Answer = answer
}
} else if res.Reason != dnsfilter.NotFilteredWhiteList && protectionEnabled {
origResp2 := d.Res
res, err = s.filterDNSResponse(d, setts)
if err != nil {
return err
}
if res != nil {
origResp = origResp2 // matched by response
} else {
res = &dnsfilter.Result{}
}
}
}
if d.Res != nil {
d.Res.Compress = true // some devices require DNS message compression
}
shouldLog := true
msg := d.Req
// don't log ANY request if refuseAny is enabled
if len(msg.Question) >= 1 && msg.Question[0].Qtype == dns.TypeANY && s.conf.RefuseAny {
shouldLog = false
}
elapsed := time.Since(start)
s.RLock()
// Synchronize access to s.queryLog and s.stats so they won't be suddenly uninitialized while in use.
// This can happen after proxy server has been stopped, but its workers haven't yet exited.
if shouldLog && s.queryLog != nil {
p := querylog.AddParams{
Question: msg,
Answer: d.Res,
OrigAnswer: origResp,
Result: res,
Elapsed: elapsed,
ClientIP: getIP(d.Addr),
}
if d.Upstream != nil {
p.Upstream = d.Upstream.Address()
}
s.queryLog.Add(p)
}
s.updateStats(d, elapsed, *res)
s.RUnlock()
return nil
}
// Get IP address from net.Addr
func getIP(addr net.Addr) net.IP {
switch addr := addr.(type) {
case *net.UDPAddr:
return addr.IP
case *net.TCPAddr:
return addr.IP
}
return nil
}
func (s *Server) updateStats(d *proxy.DNSContext, elapsed time.Duration, res dnsfilter.Result) {
if s.stats == nil {
return
}
e := stats.Entry{}
e.Domain = strings.ToLower(d.Req.Question[0].Name)
e.Domain = e.Domain[:len(e.Domain)-1] // remove last "."
switch addr := d.Addr.(type) {
case *net.UDPAddr:
e.Client = addr.IP
case *net.TCPAddr:
e.Client = addr.IP
}
e.Time = uint32(elapsed / 1000)
switch res.Reason {
case dnsfilter.NotFilteredNotFound:
fallthrough
case dnsfilter.NotFilteredWhiteList:
fallthrough
case dnsfilter.NotFilteredError:
e.Result = stats.RNotFiltered
case dnsfilter.FilteredSafeBrowsing:
e.Result = stats.RSafeBrowsing
case dnsfilter.FilteredParental:
e.Result = stats.RParental
case dnsfilter.FilteredSafeSearch:
e.Result = stats.RSafeSearch
case dnsfilter.FilteredBlackList:
fallthrough
case dnsfilter.FilteredInvalid:
fallthrough
case dnsfilter.FilteredBlockedService:
e.Result = stats.RFiltered
}
s.stats.Update(e)
}
// getClientRequestFilteringSettings lookups client filtering settings
// using the client's IP address from the DNSContext
func (s *Server) getClientRequestFilteringSettings(d *proxy.DNSContext) *dnsfilter.RequestFilteringSettings {
setts := s.dnsFilter.GetConfig()
setts.FilteringEnabled = true
if s.conf.FilterHandler != nil {
clientAddr := ipFromAddr(d.Addr)
s.conf.FilterHandler(clientAddr, &setts)
}
return &setts
}
// filterDNSRequest applies the dnsFilter and sets d.Res if the request was filtered
func (s *Server) filterDNSRequest(d *proxy.DNSContext, setts *dnsfilter.RequestFilteringSettings) (*dnsfilter.Result, error) {
req := d.Req
host := strings.TrimSuffix(req.Question[0].Name, ".")
res, err := s.dnsFilter.CheckHost(host, d.Req.Question[0].Qtype, setts)
if err != nil {
// Return immediately if there's an error
return nil, errorx.Decorate(err, "dnsfilter failed to check host '%s'", host)
} else if res.IsFiltered {
// log.Tracef("Host %s is filtered, reason - '%s', matched rule: '%s'", host, res.Reason, res.Rule)
d.Res = s.genDNSFilterMessage(d, &res)
} else if res.Reason == dnsfilter.ReasonRewrite && len(res.IPList) != 0 {
resp := s.makeResponse(req)
name := host
if len(res.CanonName) != 0 {
resp.Answer = append(resp.Answer, s.genCNAMEAnswer(req, res.CanonName))
name = res.CanonName
}
for _, ip := range res.IPList {
if req.Question[0].Qtype == dns.TypeA {
a := s.genAAnswer(req, ip)
a.Hdr.Name = dns.Fqdn(name)
resp.Answer = append(resp.Answer, a)
} else if req.Question[0].Qtype == dns.TypeAAAA {
a := s.genAAAAAnswer(req, ip)
a.Hdr.Name = dns.Fqdn(name)
resp.Answer = append(resp.Answer, a)
}
}
d.Res = resp
}
return &res, err
}
// If response contains CNAME, A or AAAA records, we apply filtering to each canonical host name or IP address.
// If this is a match, we set a new response in d.Res and return.
func (s *Server) filterDNSResponse(d *proxy.DNSContext, setts *dnsfilter.RequestFilteringSettings) (*dnsfilter.Result, error) {
for _, a := range d.Res.Answer {
host := ""
switch v := a.(type) {
case *dns.CNAME:
log.Debug("DNSFwd: Checking CNAME %s for %s", v.Target, v.Hdr.Name)
host = strings.TrimSuffix(v.Target, ".")
case *dns.A:
host = v.A.String()
log.Debug("DNSFwd: Checking record A (%s) for %s", host, v.Hdr.Name)
case *dns.AAAA:
host = v.AAAA.String()
log.Debug("DNSFwd: Checking record AAAA (%s) for %s", host, v.Hdr.Name)
default:
continue
}
s.RLock()
// Synchronize access to s.dnsFilter so it won't be suddenly uninitialized while in use.
// This could happen after proxy server has been stopped, but its workers are not yet exited.
if !s.conf.ProtectionEnabled || s.dnsFilter == nil {
s.RUnlock()
continue
}
res, err := s.dnsFilter.CheckHostRules(host, d.Req.Question[0].Qtype, setts)
s.RUnlock()
if err != nil {
return nil, err
} else if res.IsFiltered {
d.Res = s.genDNSFilterMessage(d, &res)
log.Debug("DNSFwd: Matched %s by response: %s", d.Req.Question[0].Name, host)
return &res, nil
}
}
return nil, nil
}
// Create a DNS response by DNS request and set necessary flags
func (s *Server) makeResponse(req *dns.Msg) *dns.Msg {
resp := dns.Msg{}
resp.SetReply(req)
resp.RecursionAvailable = true
resp.Compress = true
return &resp
}
// genDNSFilterMessage generates a DNS message corresponding to the filtering result
func (s *Server) genDNSFilterMessage(d *proxy.DNSContext, result *dnsfilter.Result) *dns.Msg {
m := d.Req
if m.Question[0].Qtype != dns.TypeA && m.Question[0].Qtype != dns.TypeAAAA {
return s.genNXDomain(m)
}
switch result.Reason {
case dnsfilter.FilteredSafeBrowsing:
return s.genBlockedHost(m, s.conf.SafeBrowsingBlockHost, d)
case dnsfilter.FilteredParental:
return s.genBlockedHost(m, s.conf.ParentalBlockHost, d)
default:
if result.IP != nil {
return s.genResponseWithIP(m, result.IP)
}
if s.conf.BlockingMode == "null_ip" {
switch m.Question[0].Qtype {
case dns.TypeA:
return s.genARecord(m, []byte{0, 0, 0, 0})
case dns.TypeAAAA:
return s.genAAAARecord(m, net.IPv6zero)
}
} else if s.conf.BlockingMode == "custom_ip" {
switch m.Question[0].Qtype {
case dns.TypeA:
return s.genARecord(m, s.conf.BlockingIPAddrv4)
case dns.TypeAAAA:
return s.genAAAARecord(m, s.conf.BlockingIPAddrv6)
}
}
return s.genNXDomain(m)
}
}
func (s *Server) genServerFailure(request *dns.Msg) *dns.Msg {
resp := dns.Msg{}
resp.SetRcode(request, dns.RcodeServerFailure)
resp.RecursionAvailable = true
return &resp
}
func (s *Server) genARecord(request *dns.Msg, ip net.IP) *dns.Msg {
resp := s.makeResponse(request)
resp.Answer = append(resp.Answer, s.genAAnswer(request, ip))
return resp
}
func (s *Server) genAAAARecord(request *dns.Msg, ip net.IP) *dns.Msg {
resp := s.makeResponse(request)
resp.Answer = append(resp.Answer, s.genAAAAAnswer(request, ip))
return resp
}
func (s *Server) genAAnswer(req *dns.Msg, ip net.IP) *dns.A {
answer := new(dns.A)
answer.Hdr = dns.RR_Header{
Name: req.Question[0].Name,
Rrtype: dns.TypeA,
Ttl: s.conf.BlockedResponseTTL,
Class: dns.ClassINET,
}
answer.A = ip
return answer
}
func (s *Server) genAAAAAnswer(req *dns.Msg, ip net.IP) *dns.AAAA {
answer := new(dns.AAAA)
answer.Hdr = dns.RR_Header{
Name: req.Question[0].Name,
Rrtype: dns.TypeAAAA,
Ttl: s.conf.BlockedResponseTTL,
Class: dns.ClassINET,
}
answer.AAAA = ip
return answer
}
// generate DNS response message with an IP address
func (s *Server) genResponseWithIP(req *dns.Msg, ip net.IP) *dns.Msg {
if req.Question[0].Qtype == dns.TypeA && ip.To4() != nil {
return s.genARecord(req, ip.To4())
} else if req.Question[0].Qtype == dns.TypeAAAA &&
len(ip) == net.IPv6len && ip.To4() == nil {
return s.genAAAARecord(req, ip)
}
// empty response
resp := s.makeResponse(req)
return resp
}
func (s *Server) genBlockedHost(request *dns.Msg, newAddr string, d *proxy.DNSContext) *dns.Msg {
ip := net.ParseIP(newAddr)
if ip != nil {
return s.genResponseWithIP(request, ip)
}
// look up the hostname, TODO: cache
replReq := dns.Msg{}
replReq.SetQuestion(dns.Fqdn(newAddr), request.Question[0].Qtype)
replReq.RecursionDesired = true
newContext := &proxy.DNSContext{
Proto: d.Proto,
Addr: d.Addr,
StartTime: time.Now(),
Req: &replReq,
}
err := s.dnsProxy.Resolve(newContext)
if err != nil {
log.Printf("Couldn't look up replacement host '%s': %s", newAddr, err)
return s.genServerFailure(request)
}
resp := s.makeResponse(request)
if newContext.Res != nil {
for _, answer := range newContext.Res.Answer {
answer.Header().Name = request.Question[0].Name
resp.Answer = append(resp.Answer, answer)
}
}
return resp
}
// Make a CNAME response
func (s *Server) genCNAMEAnswer(req *dns.Msg, cname string) *dns.CNAME {
answer := new(dns.CNAME)
answer.Hdr = dns.RR_Header{
Name: req.Question[0].Name,
Rrtype: dns.TypeCNAME,
Ttl: s.conf.BlockedResponseTTL,
Class: dns.ClassINET,
}
answer.Target = dns.Fqdn(cname)
return answer
}
func (s *Server) genNXDomain(request *dns.Msg) *dns.Msg {
resp := dns.Msg{}
resp.SetRcode(request, dns.RcodeNameError)
resp.RecursionAvailable = true
resp.Ns = s.genSOA(request)
return &resp
}
func (s *Server) genSOA(request *dns.Msg) []dns.RR {
zone := ""
if len(request.Question) > 0 {
zone = request.Question[0].Name
}
soa := dns.SOA{
// values copied from verisign's nonexistent .com domain
// their exact values are not important in our use case because they are used for domain transfers between primary/secondary DNS servers
Refresh: 1800,
Retry: 900,
Expire: 604800,
Minttl: 86400,
// copied from AdGuard DNS
Ns: "fake-for-negative-caching.adguard.com.",
Serial: 100500,
// rest is request-specific
Hdr: dns.RR_Header{
Name: zone,
Rrtype: dns.TypeSOA,
Ttl: s.conf.BlockedResponseTTL,
Class: dns.ClassINET,
},
Mbox: "hostmaster.", // zone will be appended later if it's not empty or "."
}
if soa.Hdr.Ttl == 0 {
soa.Hdr.Ttl = defaultValues.BlockedResponseTTL
}
if len(zone) > 0 && zone[0] != '.' {
soa.Mbox += zone
}
return []dns.RR{&soa}
}