badguardhome/dnsforward/dnsforward.go

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package dnsforward
import (
"crypto/tls"
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"errors"
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"fmt"
"net"
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"net/http"
"strings"
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"sync"
"time"
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"github.com/AdguardTeam/AdGuardHome/dnsfilter"
"github.com/AdguardTeam/AdGuardHome/stats"
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"github.com/AdguardTeam/dnsproxy/proxy"
"github.com/AdguardTeam/dnsproxy/upstream"
"github.com/AdguardTeam/golibs/log"
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"github.com/joomcode/errorx"
"github.com/miekg/dns"
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)
// DefaultTimeout is the default upstream timeout
const DefaultTimeout = 10 * time.Second
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const (
safeBrowsingBlockHost = "standard-block.dns.adguard.com"
parentalBlockHost = "family-block.dns.adguard.com"
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)
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// Server is the main way to start a DNS server.
//
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// Example:
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// 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
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//
// The zero Server is empty and ready for use.
type Server struct {
dnsProxy *proxy.Proxy // DNS proxy instance
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dnsFilter *dnsfilter.Dnsfilter // DNS filter instance
queryLog *queryLog // Query log instance
stats stats.Stats
AllowedClients map[string]bool // IP addresses of whitelist clients
DisallowedClients map[string]bool // IP addresses of clients that should be blocked
AllowedClientsIPNet []net.IPNet // CIDRs of whitelist clients
DisallowedClientsIPNet []net.IPNet // CIDRs of clients that should be blocked
BlockedHosts map[string]bool // hosts that should be blocked
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sync.RWMutex
conf ServerConfig
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}
// NewServer creates a new instance of the dnsforward.Server
// baseDir is the base directory for query logs
// Note: this function must be called only once
func NewServer(baseDir string, stats stats.Stats) *Server {
s := &Server{
queryLog: newQueryLog(baseDir),
}
s.stats = stats
log.Printf("Start DNS server periodic jobs")
go s.queryLog.periodicQueryLogRotate()
return s
}
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// FilteringConfig represents the DNS filtering configuration of AdGuard Home
// The zero FilteringConfig is empty and ready for use.
type FilteringConfig struct {
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ProtectionEnabled bool `yaml:"protection_enabled"` // whether or not use any of dnsfilter features
FilteringEnabled bool `yaml:"filtering_enabled"` // whether or not use filter lists
BlockingMode string `yaml:"blocking_mode"` // mode how to answer filtered requests
BlockedResponseTTL uint32 `yaml:"blocked_response_ttl"` // if 0, then default is used (3600)
QueryLogEnabled bool `yaml:"querylog_enabled"` // if true, query log is enabled
Ratelimit int `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
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"`
// Names of services to block (globally).
// Per-client settings can override this configuration.
BlockedServices []string `yaml:"blocked_services"`
CacheSize uint `yaml:"cache_size"` // DNS cache size (in bytes)
dnsfilter.Config `yaml:",inline"`
}
// TLSConfig is the TLS configuration for HTTPS, DNS-over-HTTPS, and DNS-over-TLS
type TLSConfig struct {
TLSListenAddr *net.TCPAddr `yaml:"-" json:"-"`
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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:"-"`
}
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// ServerConfig represents server configuration.
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// 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
Filters []dnsfilter.Filter // A list of filters to use
OnDNSRequest func(d *proxy.DNSContext)
FilteringConfig
TLSConfig
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}
// if any of ServerConfig values are zero, then default values from below are used
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var defaultValues = ServerConfig{
UDPListenAddr: &net.UDPAddr{Port: 53},
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TCPListenAddr: &net.TCPAddr{Port: 53},
FilteringConfig: FilteringConfig{BlockedResponseTTL: 3600},
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}
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func init() {
defaultDNS := []string{"8.8.8.8:53", "8.8.4.4:53"}
defaultUpstreams := make([]upstream.Upstream, 0)
for _, addr := range defaultDNS {
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u, err := upstream.AddressToUpstream(addr, upstream.Options{Timeout: DefaultTimeout})
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if err == nil {
defaultUpstreams = append(defaultUpstreams, u)
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}
}
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defaultValues.Upstreams = defaultUpstreams
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}
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// Start starts the DNS server
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func (s *Server) Start(config *ServerConfig) error {
s.Lock()
defer s.Unlock()
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return s.startInternal(config)
}
func convertArrayToMap(dst *map[string]bool, src []string) {
*dst = make(map[string]bool)
for _, s := range src {
(*dst)[s] = true
}
}
// Split array of IP or CIDR into 2 containers for fast search
func processIPCIDRArray(dst *map[string]bool, dstIPNet *[]net.IPNet, src []string) error {
*dst = make(map[string]bool)
for _, s := range src {
ip := net.ParseIP(s)
if ip != nil {
(*dst)[s] = true
continue
}
_, ipnet, err := net.ParseCIDR(s)
if err != nil {
return err
}
*dstIPNet = append(*dstIPNet, *ipnet)
}
return nil
}
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// startInternal starts without locking
func (s *Server) startInternal(config *ServerConfig) error {
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if s.dnsFilter != nil || s.dnsProxy != nil {
return errors.New("DNS server is already started")
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}
err := s.initDNSFilter(config)
if err != nil {
return err
}
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proxyConfig := proxy.Config{
UDPListenAddr: s.conf.UDPListenAddr,
TCPListenAddr: s.conf.TCPListenAddr,
Ratelimit: 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,
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}
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err = processIPCIDRArray(&s.AllowedClients, &s.AllowedClientsIPNet, s.conf.AllowedClients)
if err != nil {
return err
}
err = processIPCIDRArray(&s.DisallowedClients, &s.DisallowedClientsIPNet, s.conf.DisallowedClients)
if err != nil {
return err
}
convertArrayToMap(&s.BlockedHosts, s.conf.BlockedHosts)
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,
}
}
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if proxyConfig.UDPListenAddr == nil {
proxyConfig.UDPListenAddr = defaultValues.UDPListenAddr
}
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if proxyConfig.TCPListenAddr == nil {
proxyConfig.TCPListenAddr = defaultValues.TCPListenAddr
}
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if len(proxyConfig.Upstreams) == 0 {
proxyConfig.Upstreams = defaultValues.Upstreams
}
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// Initialize and start the DNS proxy
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s.dnsProxy = &proxy.Proxy{Config: proxyConfig}
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return s.dnsProxy.Start()
}
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// Initializes the DNS filter
func (s *Server) initDNSFilter(config *ServerConfig) error {
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log.Tracef("Creating dnsfilter")
if config != nil {
s.conf = *config
}
var filters map[int]string
filters = nil
if s.conf.FilteringEnabled {
filters = make(map[int]string)
for _, f := range s.conf.Filters {
if f.ID == 0 {
filters[int(f.ID)] = string(f.Data)
} else {
filters[int(f.ID)] = f.FilePath
}
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}
}
if len(s.conf.ParentalBlockHost) == 0 {
s.conf.ParentalBlockHost = parentalBlockHost
}
if len(s.conf.SafeBrowsingBlockHost) == 0 {
s.conf.SafeBrowsingBlockHost = safeBrowsingBlockHost
}
s.dnsFilter = dnsfilter.New(&s.conf.Config, filters)
if s.dnsFilter == nil {
return fmt.Errorf("could not initialize dnsfilter")
}
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return nil
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}
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// Stop stops the DNS server
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func (s *Server) Stop() error {
s.Lock()
defer s.Unlock()
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return s.stopInternal()
}
// stopInternal stops without locking
func (s *Server) stopInternal() error {
if s.dnsProxy != nil {
err := s.dnsProxy.Stop()
s.dnsProxy = nil
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if err != nil {
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return errorx.Decorate(err, "could not stop the DNS server properly")
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}
}
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if s.dnsFilter != nil {
s.dnsFilter.Destroy()
s.dnsFilter = nil
}
// flush remainder to file
return s.queryLog.flushLogBuffer(true)
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}
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// IsRunning returns true if the DNS server is running
func (s *Server) IsRunning() bool {
s.RLock()
isRunning := true
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if s.dnsProxy == nil {
isRunning = false
}
s.RUnlock()
return isRunning
}
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// Reconfigure applies the new configuration to the DNS server
func (s *Server) Reconfigure(config *ServerConfig) error {
s.Lock()
defer s.Unlock()
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log.Print("Start reconfiguring the server")
err := s.stopInternal()
if err != nil {
return errorx.Decorate(err, "could not reconfigure the server")
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}
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err = s.startInternal(config)
if err != nil {
return errorx.Decorate(err, "could not reconfigure the server")
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}
return nil
}
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// 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()
s.dnsProxy.ServeHTTP(w, r)
s.RUnlock()
}
// GetQueryLog returns a map with the current query log ready to be converted to a JSON
func (s *Server) GetQueryLog() []map[string]interface{} {
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s.RLock()
defer s.RUnlock()
return s.queryLog.getQueryLog()
}
// Return TRUE if this client should be blocked
func (s *Server) isBlockedIP(ip string) bool {
if len(s.AllowedClients) != 0 || len(s.AllowedClientsIPNet) != 0 {
_, ok := s.AllowedClients[ip]
if ok {
return false
}
if len(s.AllowedClientsIPNet) != 0 {
ipAddr := net.ParseIP(ip)
for _, ipnet := range s.AllowedClientsIPNet {
if ipnet.Contains(ipAddr) {
return false
}
}
}
return true
}
_, ok := s.DisallowedClients[ip]
if ok {
return true
}
if len(s.DisallowedClientsIPNet) != 0 {
ipAddr := net.ParseIP(ip)
for _, ipnet := range s.DisallowedClientsIPNet {
if ipnet.Contains(ipAddr) {
return true
}
}
}
return false
}
// Return TRUE if this domain should be blocked
func (s *Server) isBlockedDomain(host string) bool {
_, ok := s.BlockedHosts[host]
return ok
}
func (s *Server) beforeRequestHandler(p *proxy.Proxy, d *proxy.DNSContext) (bool, error) {
ip, _, _ := net.SplitHostPort(d.Addr.String())
if s.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.isBlockedDomain(host) {
log.Tracef("Domain %s is blocked by settings", host)
return false, nil
}
}
return true, nil
}
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// handleDNSRequest filters the incoming DNS requests and writes them to the query log
func (s *Server) handleDNSRequest(p *proxy.Proxy, d *proxy.DNSContext) error {
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start := time.Now()
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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
}
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// 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).
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res, err := s.filterDNSRequest(d)
s.RUnlock()
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if err != nil {
return err
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}
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if d.Res == nil {
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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)
}
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// request was not filtered so let it be processed further
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err = p.Resolve(d)
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if err != nil {
return err
}
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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
}
}
}
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shouldLog := true
msg := d.Req
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// don't log ANY request if refuseAny is enabled
if len(msg.Question) >= 1 && msg.Question[0].Qtype == dns.TypeANY && s.conf.RefuseAny {
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shouldLog = false
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}
elapsed := time.Since(start)
if s.conf.QueryLogEnabled && shouldLog {
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upstreamAddr := ""
if d.Upstream != nil {
upstreamAddr = d.Upstream.Address()
}
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_ = s.queryLog.logRequest(msg, d.Res, res, elapsed, d.Addr, upstreamAddr)
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}
s.updateStats(d, elapsed, *res)
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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)
}
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// filterDNSRequest applies the dnsFilter and sets d.Res if the request was filtered
func (s *Server) filterDNSRequest(d *proxy.DNSContext) (*dnsfilter.Result, error) {
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var res dnsfilter.Result
req := d.Req
host := strings.TrimSuffix(req.Question[0].Name, ".")
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dnsFilter := s.dnsFilter
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if !s.conf.ProtectionEnabled || s.dnsFilter == nil {
return &dnsfilter.Result{}, nil
}
var err error
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clientAddr := ""
if d.Addr != nil {
clientAddr, _, _ = net.SplitHostPort(d.Addr.String())
}
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var setts dnsfilter.RequestFilteringSettings
setts.FilteringEnabled = true
setts.SafeSearchEnabled = s.conf.SafeSearchEnabled
setts.SafeBrowsingEnabled = s.conf.SafeBrowsingEnabled
setts.ParentalEnabled = s.conf.ParentalEnabled
if s.conf.FilterHandler != nil {
s.conf.FilterHandler(clientAddr, &setts)
}
res, err = dnsFilter.CheckHost(host, d.Req.Question[0].Qtype, &setts)
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if err != nil {
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// Return immediately if there's an error
return nil, errorx.Decorate(err, "dnsfilter failed to check host '%s'", host)
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} else if res.IsFiltered {
// log.Tracef("Host %s is filtered, reason - '%s', matched rule: '%s'", host, res.Reason, res.Rule)
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d.Res = s.genDNSFilterMessage(d, &res)
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} else if res.Reason == dnsfilter.ReasonRewrite && len(res.IPList) != 0 {
resp := dns.Msg{}
resp.SetReply(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, res.IP)
a.Hdr.Name = dns.Fqdn(name)
resp.Answer = append(resp.Answer, a)
}
}
d.Res = &resp
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}
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return &res, err
}
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// 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 {
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return s.genNXDomain(m)
}
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switch result.Reason {
case dnsfilter.FilteredSafeBrowsing:
return s.genBlockedHost(m, s.conf.SafeBrowsingBlockHost, d)
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case dnsfilter.FilteredParental:
return s.genBlockedHost(m, s.conf.ParentalBlockHost, d)
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default:
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if result.IP != nil {
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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)
}
}
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return s.genNXDomain(m)
}
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}
func (s *Server) genServerFailure(request *dns.Msg) *dns.Msg {
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resp := dns.Msg{}
resp.SetRcode(request, dns.RcodeServerFailure)
resp.RecursionAvailable = true
return &resp
}
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func (s *Server) genARecord(request *dns.Msg, ip net.IP) *dns.Msg {
resp := dns.Msg{}
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resp.SetReply(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 := dns.Msg{}
resp.SetReply(request)
resp.Answer = append(resp.Answer, s.genAAAAAnswer(request, ip))
return &resp
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}
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 && ip.To4() == nil {
return s.genAAAARecord(req, ip)
}
// empty response
resp := dns.Msg{}
resp.SetReply(req)
return &resp
}
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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
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newContext := &proxy.DNSContext{
Proto: d.Proto,
Addr: d.Addr,
StartTime: time.Now(),
Req: &replReq,
}
err := s.dnsProxy.Resolve(newContext)
if err != nil {
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log.Printf("Couldn't look up replacement host '%s': %s", newAddr, err)
return s.genServerFailure(request)
}
resp := dns.Msg{}
resp.SetReply(request)
resp.Authoritative, resp.RecursionAvailable = true, true
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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
}
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// 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 {
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resp := dns.Msg{}
resp.SetRcode(request, dns.RcodeNameError)
resp.RecursionAvailable = true
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resp.Ns = s.genSOA(request)
return &resp
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}
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,
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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
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}
if len(zone) > 0 && zone[0] != '.' {
soa.Mbox += zone
}
return []dns.RR{&soa}
}