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dnsforward.go
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dnsforward.go
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// Package dnsforward contains a DNS forwarding server.
package dnsforward
import (
"fmt"
"net"
"net/http"
"net/netip"
"runtime"
"strings"
"sync"
"time"
"github.com/AdguardTeam/AdGuardHome/internal/aghalg"
"github.com/AdguardTeam/AdGuardHome/internal/aghnet"
"github.com/AdguardTeam/AdGuardHome/internal/dhcpd"
"github.com/AdguardTeam/AdGuardHome/internal/filtering"
"github.com/AdguardTeam/AdGuardHome/internal/querylog"
"github.com/AdguardTeam/AdGuardHome/internal/stats"
"github.com/AdguardTeam/dnsproxy/proxy"
"github.com/AdguardTeam/dnsproxy/upstream"
"github.com/AdguardTeam/golibs/cache"
"github.com/AdguardTeam/golibs/errors"
"github.com/AdguardTeam/golibs/log"
"github.com/AdguardTeam/golibs/netutil"
"github.com/AdguardTeam/golibs/stringutil"
"github.com/miekg/dns"
)
// DefaultTimeout is the default upstream timeout
const DefaultTimeout = 10 * time.Second
// defaultClientIDCacheCount is the default count of items in the LRU ClientID
// cache. The assumption here is that there won't be more than this many
// requests between the BeforeRequestHandler stage and the actual processing.
const defaultClientIDCacheCount = 1024
var defaultDNS = []string{
"https://dns10.quad9.net/dns-query",
}
var defaultBootstrap = []string{"9.9.9.10", "149.112.112.10", "2620:fe::10", "2620:fe::fe:10"}
// Often requested by all kinds of DNS probes
var defaultBlockedHosts = []string{"version.bind", "id.server", "hostname.bind"}
var webRegistered bool
// hostToIPTable is a convenient type alias for tables of host names to an IP
// address.
type hostToIPTable = map[string]netip.Addr
// ipToHostTable is a convenient type alias for tables of IP addresses to their
// host names. For example, for use with PTR queries.
type ipToHostTable = map[netip.Addr]string
// 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 *filtering.DNSFilter // DNS filter instance
dhcpServer dhcpd.Interface // DHCP server instance (optional)
queryLog querylog.QueryLog // Query log instance
stats stats.Interface
access *accessManager
// localDomainSuffix is the suffix used to detect internal hosts. It
// must be a valid domain name plus dots on each side.
localDomainSuffix string
ipset ipsetCtx
privateNets netutil.SubnetSet
localResolvers *proxy.Proxy
sysResolvers aghnet.SystemResolvers
recDetector *recursionDetector
// anonymizer masks the client's IP addresses if needed.
anonymizer *aghnet.IPMut
tableHostToIP hostToIPTable
tableHostToIPLock sync.Mutex
tableIPToHost ipToHostTable
tableIPToHostLock sync.Mutex
// clientIDCache is a temporary storage for ClientIDs that were extracted
// during the BeforeRequestHandler stage.
clientIDCache cache.Cache
// DNS proxy instance for internal usage
// We don't Start() it and so no listen port is required.
internalProxy *proxy.Proxy
isRunning bool
conf ServerConfig
// serverLock protects Server.
serverLock sync.RWMutex
}
// defaultLocalDomainSuffix is the default suffix used to detect internal hosts
// when no suffix is provided.
//
// See the documentation for Server.localDomainSuffix.
const defaultLocalDomainSuffix = "lan"
// DNSCreateParams are parameters to create a new server.
type DNSCreateParams struct {
DNSFilter *filtering.DNSFilter
Stats stats.Interface
QueryLog querylog.QueryLog
DHCPServer dhcpd.Interface
PrivateNets netutil.SubnetSet
Anonymizer *aghnet.IPMut
LocalDomain string
}
const (
// recursionTTL is the time recursive request is cached for.
recursionTTL = 1 * time.Second
// cachedRecurrentReqNum is the maximum number of cached recurrent
// requests.
cachedRecurrentReqNum = 1000
)
// NewServer creates a new instance of the dnsforward.Server
// Note: this function must be called only once
func NewServer(p DNSCreateParams) (s *Server, err error) {
var localDomainSuffix string
if p.LocalDomain == "" {
localDomainSuffix = defaultLocalDomainSuffix
} else {
err = netutil.ValidateDomainName(p.LocalDomain)
if err != nil {
return nil, fmt.Errorf("local domain: %w", err)
}
localDomainSuffix = p.LocalDomain
}
if p.Anonymizer == nil {
p.Anonymizer = aghnet.NewIPMut(nil)
}
s = &Server{
dnsFilter: p.DNSFilter,
stats: p.Stats,
queryLog: p.QueryLog,
privateNets: p.PrivateNets,
localDomainSuffix: localDomainSuffix,
recDetector: newRecursionDetector(recursionTTL, cachedRecurrentReqNum),
clientIDCache: cache.New(cache.Config{
EnableLRU: true,
MaxCount: defaultClientIDCacheCount,
}),
anonymizer: p.Anonymizer,
}
// TODO(e.burkov): Enable the refresher after the actual implementation
// passes the public testing.
s.sysResolvers, err = aghnet.NewSystemResolvers(nil)
if err != nil {
return nil, fmt.Errorf("initializing system resolvers: %w", err)
}
if p.DHCPServer != nil {
s.dhcpServer = p.DHCPServer
s.dhcpServer.SetOnLeaseChanged(s.onDHCPLeaseChanged)
s.onDHCPLeaseChanged(dhcpd.LeaseChangedAdded)
}
if runtime.GOARCH == "mips" || runtime.GOARCH == "mipsle" {
// Use plain DNS on MIPS, encryption is too slow
defaultDNS = defaultBootstrap
}
return s, nil
}
// Close gracefully closes the server. It is safe for concurrent use.
//
// TODO(e.burkov): A better approach would be making Stop method waiting for all
// its workers finished. But it would require the upstream.Upstream to have the
// Close method to prevent from hanging while waiting for unresponsive server to
// respond.
func (s *Server) Close() {
s.serverLock.Lock()
defer s.serverLock.Unlock()
s.dnsFilter = nil
s.stats = nil
s.queryLog = nil
s.dnsProxy = nil
if err := s.ipset.close(); err != nil {
log.Error("closing ipset: %s", err)
}
}
// WriteDiskConfig - write configuration
func (s *Server) WriteDiskConfig(c *FilteringConfig) {
s.serverLock.RLock()
defer s.serverLock.RUnlock()
sc := s.conf.FilteringConfig
*c = sc
c.RatelimitWhitelist = stringutil.CloneSlice(sc.RatelimitWhitelist)
c.BootstrapDNS = stringutil.CloneSlice(sc.BootstrapDNS)
c.AllowedClients = stringutil.CloneSlice(sc.AllowedClients)
c.DisallowedClients = stringutil.CloneSlice(sc.DisallowedClients)
c.BlockedHosts = stringutil.CloneSlice(sc.BlockedHosts)
c.TrustedProxies = stringutil.CloneSlice(sc.TrustedProxies)
c.UpstreamDNS = stringutil.CloneSlice(sc.UpstreamDNS)
}
// RDNSSettings returns the copy of actual RDNS configuration.
func (s *Server) RDNSSettings() (localPTRResolvers []string, resolveClients, resolvePTR bool) {
s.serverLock.RLock()
defer s.serverLock.RUnlock()
return stringutil.CloneSlice(s.conf.LocalPTRResolvers),
s.conf.ResolveClients,
s.conf.UsePrivateRDNS
}
// 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.serverLock.RLock()
defer s.serverLock.RUnlock()
return s.internalProxy.LookupIPAddr(host)
}
// RDNSExchanger is a resolver for clients' addresses.
type RDNSExchanger interface {
// Exchange tries to resolve the ip in a suitable way, e.g. either as
// local or as external.
Exchange(ip net.IP) (host string, err error)
// ResolvesPrivatePTR returns true if the RDNSExchanger is able to
// resolve PTR requests for locally-served addresses.
ResolvesPrivatePTR() (ok bool)
}
const (
// rDNSEmptyAnswerErr is returned by Exchange method when the answer
// section of respond is empty.
rDNSEmptyAnswerErr errors.Error = "the answer section is empty"
// rDNSNotPTRErr is returned by Exchange method when the response is not
// of PTR type.
rDNSNotPTRErr errors.Error = "the response is not a ptr"
)
// type check
var _ RDNSExchanger = (*Server)(nil)
// Exchange implements the RDNSExchanger interface for *Server.
func (s *Server) Exchange(ip net.IP) (host string, err error) {
s.serverLock.RLock()
defer s.serverLock.RUnlock()
if !s.conf.ResolveClients {
return "", nil
}
arpa, err := netutil.IPToReversedAddr(ip)
if err != nil {
return "", fmt.Errorf("reversing ip: %w", err)
}
arpa = dns.Fqdn(arpa)
req := &dns.Msg{
MsgHdr: dns.MsgHdr{
Id: dns.Id(),
RecursionDesired: true,
},
Compress: true,
Question: []dns.Question{{
Name: arpa,
Qtype: dns.TypePTR,
Qclass: dns.ClassINET,
}},
}
ctx := &proxy.DNSContext{
Proto: "udp",
Req: req,
StartTime: time.Now(),
}
var resolver *proxy.Proxy
if s.privateNets.Contains(ip) {
if !s.conf.UsePrivateRDNS {
return "", nil
}
resolver = s.localResolvers
s.recDetector.add(*req)
} else {
resolver = s.internalProxy
}
if err = resolver.Resolve(ctx); err != nil {
return "", err
}
resp := ctx.Res
if len(resp.Answer) == 0 {
return "", fmt.Errorf("lookup for %q: %w", arpa, rDNSEmptyAnswerErr)
}
ptr, ok := resp.Answer[0].(*dns.PTR)
if !ok {
return "", fmt.Errorf("type checking: %w", rDNSNotPTRErr)
}
return strings.TrimSuffix(ptr.Ptr, "."), nil
}
// ResolvesPrivatePTR implements the RDNSExchanger interface for *Server.
func (s *Server) ResolvesPrivatePTR() (ok bool) {
s.serverLock.RLock()
defer s.serverLock.RUnlock()
return s.conf.UsePrivateRDNS
}
// Start starts the DNS server.
func (s *Server) Start() error {
s.serverLock.Lock()
defer s.serverLock.Unlock()
return s.startLocked()
}
// startLocked starts the DNS server without locking. For internal use only.
func (s *Server) startLocked() error {
err := s.dnsProxy.Start()
if err == nil {
s.isRunning = true
}
return err
}
// defaultLocalTimeout is the default timeout for resolving addresses from
// locally-served networks. It is assumed that local resolvers should work much
// faster than ordinary upstreams.
const defaultLocalTimeout = 1 * time.Second
// collectDNSIPAddrs returns IP addresses the server is listening on without
// port numbers. For internal use only.
func (s *Server) collectDNSIPAddrs() (addrs []string, err error) {
addrs = make([]string, len(s.conf.TCPListenAddrs)+len(s.conf.UDPListenAddrs))
var i int
var ip net.IP
for _, addr := range s.conf.TCPListenAddrs {
if addr == nil {
continue
}
if ip = addr.IP; ip.IsUnspecified() {
return aghnet.CollectAllIfacesAddrs()
}
addrs[i] = ip.String()
i++
}
for _, addr := range s.conf.UDPListenAddrs {
if addr == nil {
continue
}
if ip = addr.IP; ip.IsUnspecified() {
return aghnet.CollectAllIfacesAddrs()
}
addrs[i] = ip.String()
i++
}
return addrs[:i], nil
}
func (s *Server) filterOurDNSAddrs(addrs []string) (filtered []string, err error) {
var ourAddrs []string
ourAddrs, err = s.collectDNSIPAddrs()
if err != nil {
return nil, err
}
ourAddrsSet := stringutil.NewSet(ourAddrs...)
// TODO(e.burkov): The approach of subtracting sets of strings is not
// really applicable here since in case of listening on all network
// interfaces we should check the whole interface's network to cut off
// all the loopback addresses as well.
return stringutil.FilterOut(addrs, ourAddrsSet.Has), nil
}
// setupResolvers initializes the resolvers for local addresses. For internal
// use only.
func (s *Server) setupResolvers(localAddrs []string) (err error) {
bootstraps := s.conf.BootstrapDNS
if len(localAddrs) == 0 {
localAddrs = s.sysResolvers.Get()
bootstraps = nil
}
localAddrs, err = s.filterOurDNSAddrs(localAddrs)
if err != nil {
return err
}
log.Debug("upstreams to resolve PTR for local addresses: %v", localAddrs)
var upsConfig *proxy.UpstreamConfig
upsConfig, err = proxy.ParseUpstreamsConfig(
localAddrs,
&upstream.Options{
Bootstrap: bootstraps,
Timeout: defaultLocalTimeout,
// TODO(e.burkov): Should we verify server's certificates?
},
)
if err != nil {
return fmt.Errorf("parsing upstreams: %w", err)
}
s.localResolvers = &proxy.Proxy{
Config: proxy.Config{
UpstreamConfig: upsConfig,
},
}
return nil
}
// Prepare initializes parameters of s using data from conf. conf must not be
// nil.
func (s *Server) Prepare(conf *ServerConfig) (err error) {
s.conf = *conf
err = validateBlockingMode(s.conf.BlockingMode, s.conf.BlockingIPv4, s.conf.BlockingIPv6)
if err != nil {
return fmt.Errorf("checking blocking mode: %w", err)
}
s.initDefaultSettings()
err = s.prepareIpsetListSettings()
if err != nil {
// Don't wrap the error, because it's informative enough as is.
return fmt.Errorf("preparing ipset settings: %w", err)
}
err = s.prepareUpstreamSettings()
if err != nil {
return fmt.Errorf("preparing upstream settings: %w", err)
}
var proxyConfig proxy.Config
proxyConfig, err = s.createProxyConfig()
if err != nil {
return fmt.Errorf("preparing proxy: %w", err)
}
err = s.prepareInternalProxy()
if err != nil {
return fmt.Errorf("preparing internal proxy: %w", err)
}
s.access, err = newAccessCtx(
s.conf.AllowedClients,
s.conf.DisallowedClients,
s.conf.BlockedHosts,
)
if err != nil {
return fmt.Errorf("preparing access: %w", err)
}
if !webRegistered && s.conf.HTTPRegister != nil {
webRegistered = true
s.registerHandlers()
}
s.dnsProxy = &proxy.Proxy{Config: proxyConfig}
err = s.setupResolvers(s.conf.LocalPTRResolvers)
if err != nil {
return fmt.Errorf("setting up resolvers: %w", err)
}
s.recDetector.clear()
return nil
}
// validateBlockingMode returns an error if the blocking mode data aren't valid.
func validateBlockingMode(mode BlockingMode, blockingIPv4, blockingIPv6 net.IP) (err error) {
switch mode {
case
BlockingModeDefault,
BlockingModeNXDOMAIN,
BlockingModeREFUSED,
BlockingModeNullIP:
return nil
case BlockingModeCustomIP:
if blockingIPv4 == nil {
return fmt.Errorf("blocking_ipv4 must be set when blocking_mode is custom_ip")
} else if blockingIPv6 == nil {
return fmt.Errorf("blocking_ipv6 must be set when blocking_mode is custom_ip")
}
return nil
default:
return fmt.Errorf("bad blocking mode %q", mode)
}
}
// prepareInternalProxy initializes the DNS proxy that is used for internal DNS
// queries, such as public clients PTR resolving and updater hostname resolving.
func (s *Server) prepareInternalProxy() (err error) {
conf := &proxy.Config{
CacheEnabled: true,
CacheSizeBytes: 4096,
UpstreamConfig: s.conf.UpstreamConfig,
MaxGoroutines: int(s.conf.MaxGoroutines),
}
srvConf := s.conf
setProxyUpstreamMode(
conf,
srvConf.AllServers,
srvConf.FastestAddr,
srvConf.FastestTimeout.Duration,
)
// TODO(a.garipov): Make a proper constructor for proxy.Proxy.
p := &proxy.Proxy{
Config: *conf,
}
err = p.Init()
if err != nil {
return err
}
s.internalProxy = p
return nil
}
// Stop stops the DNS server.
func (s *Server) Stop() error {
s.serverLock.Lock()
defer s.serverLock.Unlock()
return s.stopLocked()
}
// stopLocked stops the DNS server without locking. For internal use only.
func (s *Server) stopLocked() (err error) {
if s.dnsProxy != nil {
err = s.dnsProxy.Stop()
if err != nil {
return fmt.Errorf("closing primary resolvers: %w", err)
}
}
var errs []error
if upsConf := s.internalProxy.UpstreamConfig; upsConf != nil {
const action = "closing internal resolvers"
err = upsConf.Close()
if err != nil {
if errors.Is(err, net.ErrClosed) {
log.Debug("dnsforward: %s: %s", action, err)
} else {
errs = append(errs, fmt.Errorf("%s: %w", action, err))
}
}
}
if upsConf := s.localResolvers.UpstreamConfig; upsConf != nil {
const action = "closing local resolvers"
err = upsConf.Close()
if err != nil {
if errors.Is(err, net.ErrClosed) {
log.Debug("dnsforward: %s: %s", action, err)
} else {
errs = append(errs, fmt.Errorf("%s: %w", action, err))
}
}
}
if len(errs) > 0 {
return errors.List("stopping dns server", errs...)
} else {
s.isRunning = false
}
return nil
}
// IsRunning returns true if the DNS server is running.
func (s *Server) IsRunning() bool {
s.serverLock.RLock()
defer s.serverLock.RUnlock()
return s.isRunning
}
// srvClosedErr is returned when the method can't complete without inaccessible
// data from the closing server.
const srvClosedErr errors.Error = "server is closed"
// proxy returns a pointer to the current DNS proxy instance. If p is nil, the
// server is closing.
//
// See https://github.com/AdguardTeam/AdGuardHome/issues/3655.
func (s *Server) proxy() (p *proxy.Proxy) {
s.serverLock.RLock()
defer s.serverLock.RUnlock()
return s.dnsProxy
}
// Reconfigure applies the new configuration to the DNS server.
func (s *Server) Reconfigure(conf *ServerConfig) error {
s.serverLock.Lock()
defer s.serverLock.Unlock()
log.Print("Start reconfiguring the server")
err := s.stopLocked()
if err != nil {
return fmt.Errorf("could not reconfigure the server: %w", err)
}
// 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)
// TODO(a.garipov): This whole piece of API is weird and needs to be remade.
if conf == nil {
conf = &s.conf
}
err = s.Prepare(conf)
if err != nil {
return fmt.Errorf("could not reconfigure the server: %w", err)
}
err = s.startLocked()
if err != nil {
return fmt.Errorf("could not reconfigure the server: %w", err)
}
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) {
if prx := s.proxy(); prx != nil {
prx.ServeHTTP(w, r)
}
}
// IsBlockedClient returns true if the client is blocked by the current access
// settings.
func (s *Server) IsBlockedClient(ip netip.Addr, clientID string) (blocked bool, rule string) {
s.serverLock.RLock()
defer s.serverLock.RUnlock()
blockedByIP := false
if ip != (netip.Addr{}) {
blockedByIP, rule = s.access.isBlockedIP(ip)
}
allowlistMode := s.access.allowlistMode()
blockedByClientID := s.access.isBlockedClientID(clientID)
// Allow if at least one of the checks allows in allowlist mode, but block
// if at least one of the checks blocks in blocklist mode.
if allowlistMode && blockedByIP && blockedByClientID {
log.Debug("client %v (id %q) is not in access allowlist", ip, clientID)
// Return now without substituting the empty rule for the
// clientID because the rule can't be empty here.
return true, rule
} else if !allowlistMode && (blockedByIP || blockedByClientID) {
log.Debug("client %v (id %q) is in access blocklist", ip, clientID)
blocked = true
}
return blocked, aghalg.Coalesce(rule, clientID)
}