AdGuardHome/internal/dnsforward/dns.go

567 lines
14 KiB
Go

package dnsforward
import (
"errors"
"net"
"strings"
"time"
"github.com/AdguardTeam/AdGuardHome/internal/aghnet"
"github.com/AdguardTeam/AdGuardHome/internal/dhcpd"
"github.com/AdguardTeam/AdGuardHome/internal/dnsfilter"
"github.com/AdguardTeam/dnsproxy/proxy"
"github.com/AdguardTeam/golibs/log"
"github.com/miekg/dns"
)
// To transfer information between modules
type dnsContext struct {
// TODO(a.garipov): Remove this and rewrite processors to be methods of
// *Server instead.
srv *Server
proxyCtx *proxy.DNSContext
// setts are the filtering settings for the client.
setts *dnsfilter.FilteringSettings
startTime time.Time
result *dnsfilter.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
// was successfully parsed.
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
// 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
// origReqDNSSEC shows if the DNSSEC flag in the original request from
// the client is set.
origReqDNSSEC 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{
srv: s,
proxyCtx: d,
result: &dnsfilter.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{
processInitial,
s.processInternalHosts,
s.processRestrictLocal,
s.processInternalIPAddrs,
processClientID,
processFilteringBeforeRequest,
s.processLocalPTR,
processUpstream,
processDNSSECAfterResponse,
processFilteringAfterResponse,
s.ipset.process,
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
}
// Perform initial checks; process WHOIS & rDNS
func processInitial(ctx *dnsContext) (rc resultCode) {
s := ctx.srv
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
}
return resultCodeSuccess
}
// Return TRUE if host names doesn't contain disallowed characters
func isHostnameOK(hostname string) bool {
for _, c := range hostname {
if !((c >= 'a' && c <= 'z') ||
(c >= 'A' && c <= 'Z') ||
(c >= '0' && c <= '9') ||
c == '.' || c == '-') {
log.Debug("dns: skipping invalid hostname %s from DHCP", hostname)
return false
}
}
return true
}
func (s *Server) onDHCPLeaseChanged(flags int) {
switch flags {
case dhcpd.LeaseChangedAdded,
dhcpd.LeaseChangedAddedStatic,
dhcpd.LeaseChangedRemovedStatic:
//
default:
return
}
hostToIP := make(map[string]net.IP)
m := make(map[string]string)
ll := s.dhcpServer.Leases(dhcpd.LeasesAll)
for _, l := range ll {
if len(l.Hostname) == 0 || !isHostnameOK(l.Hostname) {
continue
}
lowhost := strings.ToLower(l.Hostname)
m[l.IP.String()] = lowhost
ip := make(net.IP, 4)
copy(ip, l.IP.To4())
hostToIP[lowhost] = ip
}
log.Debug("dns: added %d A/PTR entries from DHCP", len(m))
s.tableHostToIPLock.Lock()
s.tableHostToIP = hostToIP
s.tableHostToIPLock.Unlock()
s.tablePTRLock.Lock()
s.tablePTR = m
s.tablePTRLock.Unlock()
}
// 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) {
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 asnwer and not NXDOMAIN.
if q.Qtype != dns.TypeA && q.Qtype != dns.TypeAAAA {
return resultCodeSuccess
}
reqHost := strings.ToLower(q.Name)
host := strings.TrimSuffix(reqHost, s.autohostSuffix)
if host == reqHost {
return resultCodeSuccess
}
// TODO(e.burkov): Restrict the access for external clients.
ip, ok := s.hostToIP(host)
if !ok {
return resultCodeSuccess
}
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 empty answers 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 := aghnet.UnreverseAddr(q.Name)
if ip == nil {
// That's weird.
//
// TODO(e.burkov): Research the cases when it could happen.
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 unaccessable externally.
if s.subnetDetector.IsLocallyServedNetwork(ip) {
clientIP := IPFromAddr(d.Addr)
if !s.subnetDetector.IsLocallyServedNetwork(clientIP) {
log.Debug("dns: %q requests for internal ip", clientIP)
d.Res = s.makeResponse(req)
// Do not even put into query log.
return resultCodeFinish
}
}
// Do not perform unreversing ever again.
ctx.unreversedReqIP = ip
// Disable redundant filtering.
filterSetts := s.getClientRequestFilteringSettings(ctx)
filterSetts.ParentalEnabled = false
filterSetts.SafeBrowsingEnabled = false
filterSetts.SafeSearchEnabled = false
filterSetts.ServicesRules = nil
ctx.setts = filterSetts
// 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.tablePTRLock.Lock()
defer s.tablePTRLock.Unlock()
if s.tablePTR == nil {
return "", false
}
host, ok = s.tablePTR[ip.String()]
return host, ok
}
// 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
}
if !s.subnetDetector.IsLocallyServedNetwork(ip) {
return resultCodeSuccess
}
req := d.Req
resp, err := s.localResolvers.Exchange(req)
if err != nil {
if errors.Is(err, aghnet.NoUpstreamsErr) {
d.Res = s.genNXDomain(req)
return resultCodeFinish
}
ctx.err = err
return resultCodeError
}
d.Res = resp
return resultCodeSuccess
}
// Apply filtering logic
func processFilteringBeforeRequest(ctx *dnsContext) (rc resultCode) {
s := ctx.srv
d := ctx.proxyCtx
if d.Res != nil {
return resultCodeSuccess // response is already set - nothing to do
}
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 err error
ctx.protectionEnabled = s.conf.ProtectionEnabled && s.dnsFilter != nil
if ctx.protectionEnabled {
if ctx.setts == nil {
ctx.setts = s.getClientRequestFilteringSettings(ctx)
}
ctx.result, err = s.filterDNSRequest(ctx)
}
s.RUnlock()
if err != nil {
ctx.err = err
return resultCodeError
}
return resultCodeSuccess
}
// processUpstream passes request to upstream servers and handles the response.
func processUpstream(ctx *dnsContext) (rc resultCode) {
s := ctx.srv
d := ctx.proxyCtx
if d.Res != nil {
return resultCodeSuccess // response is already set - nothing to do
}
if d.Addr != nil && s.conf.GetCustomUpstreamByClient != nil {
clientIP := IPStringFromAddr(d.Addr)
upstreamsConf := s.conf.GetCustomUpstreamByClient(clientIP)
if upstreamsConf != nil {
log.Debug("Using custom upstreams for %s", clientIP)
d.CustomUpstreamConfig = upstreamsConf
}
}
if s.conf.EnableDNSSEC {
opt := d.Req.IsEdns0()
if opt == nil {
log.Debug("dns: Adding OPT record with DNSSEC flag")
d.Req.SetEdns0(4096, true)
} else if !opt.Do() {
opt.SetDo(true)
} else {
ctx.origReqDNSSEC = true
}
}
// request was not filtered so let it be processed further
err := s.dnsProxy.Resolve(d)
if err != nil {
ctx.err = err
return resultCodeError
}
ctx.responseFromUpstream = true
return resultCodeSuccess
}
// Process DNSSEC after response from upstream server
func processDNSSECAfterResponse(ctx *dnsContext) (rc resultCode) {
d := ctx.proxyCtx
if !ctx.responseFromUpstream || // don't process response if it's not from upstream servers
!ctx.srv.conf.EnableDNSSEC {
return resultCodeSuccess
}
if !ctx.origReqDNSSEC {
optResp := d.Res.IsEdns0()
if optResp != nil && !optResp.Do() {
return resultCodeSuccess
}
// Remove RRSIG records from response
// because there is no DO flag in the original request from client,
// but we have EnableDNSSEC set, so we have set DO flag ourselves,
// and now we have to clean up the DNS records our client didn't ask for.
answers := []dns.RR{}
for _, a := range d.Res.Answer {
switch a.(type) {
case *dns.RRSIG:
log.Debug("Removing RRSIG record from response: %v", a)
default:
answers = append(answers, a)
}
}
d.Res.Answer = answers
answers = []dns.RR{}
for _, a := range d.Res.Ns {
switch a.(type) {
case *dns.RRSIG:
log.Debug("Removing RRSIG record from response: %v", a)
default:
answers = append(answers, a)
}
}
d.Res.Ns = answers
}
return resultCodeSuccess
}
// Apply filtering logic after we have received response from upstream servers
func processFilteringAfterResponse(ctx *dnsContext) (rc resultCode) {
s := ctx.srv
d := ctx.proxyCtx
res := ctx.result
var err error
switch res.Reason {
case dnsfilter.Rewritten,
dnsfilter.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] = ctx.origQuestion
d.Res.Question[0] = ctx.origQuestion
if len(d.Res.Answer) != 0 {
answer := []dns.RR{}
answer = append(answer, s.genAnswerCNAME(d.Req, res.CanonName))
answer = append(answer, d.Res.Answer...)
d.Res.Answer = answer
}
case dnsfilter.NotFilteredAllowList:
// nothing
default:
if !ctx.protectionEnabled || // filters are disabled: there's nothing to check for
!ctx.responseFromUpstream { // only check response if it's from an upstream server
break
}
origResp2 := d.Res
ctx.result, err = s.filterDNSResponse(ctx)
if err != nil {
ctx.err = err
return resultCodeError
}
if ctx.result != nil {
ctx.origResp = origResp2 // matched by response
} else {
ctx.result = &dnsfilter.Result{}
}
}
return resultCodeSuccess
}