badguardhome/dnsforward/handle_dns.go

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package dnsforward
import (
"net"
"strings"
"time"
"github.com/AdguardTeam/AdGuardHome/dhcpd"
"github.com/AdguardTeam/AdGuardHome/dnsfilter"
"github.com/AdguardTeam/AdGuardHome/util"
"github.com/AdguardTeam/dnsproxy/proxy"
"github.com/AdguardTeam/golibs/log"
"github.com/miekg/dns"
)
// To transfer information between modules
type dnsContext struct {
srv *Server
proxyCtx *proxy.DNSContext
setts *dnsfilter.RequestFilteringSettings // filtering settings for this client
startTime time.Time
result *dnsfilter.Result
origResp *dns.Msg // response received from upstream servers. Set when response is modified by filtering
origQuestion dns.Question // question received from client. Set when Rewrites are used.
err error // error returned from the module
protectionEnabled bool // filtering is enabled, dnsfilter object is ready
responseFromUpstream bool // response is received from upstream servers
origReqDNSSEC bool // DNSSEC flag in the original request from user
}
const (
resultDone = iota // module has completed its job, continue
resultFinish // module has completed its job, exit normally
resultError // an error occurred, exit with an error
)
// 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}
ctx.result = &dnsfilter.Result{}
ctx.startTime = time.Now()
type modProcessFunc func(ctx *dnsContext) int
mods := []modProcessFunc{
processInitial,
processInternalHosts,
processInternalIPAddrs,
processFilteringBeforeRequest,
processUpstream,
processDNSSECAfterResponse,
processFilteringAfterResponse,
processQueryLogsAndStats,
}
for _, process := range mods {
r := process(ctx)
switch r {
case resultDone:
// continue: call the next filter
case resultFinish:
return nil
case resultError:
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) int {
s := ctx.srv
d := ctx.proxyCtx
if s.conf.AAAADisabled && d.Req.Question[0].Qtype == dns.TypeAAAA {
_ = proxy.CheckDisabledAAAARequest(d, true)
return resultFinish
}
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 resultFinish
}
return resultDone
}
// 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()
}
// Respond to A requests if the target host name is associated with a lease from our DHCP server
func processInternalHosts(ctx *dnsContext) int {
s := ctx.srv
req := ctx.proxyCtx.Req
if !(req.Question[0].Qtype == dns.TypeA || req.Question[0].Qtype == dns.TypeAAAA) {
return resultDone
}
host := req.Question[0].Name
host = strings.ToLower(host)
if !strings.HasSuffix(host, ".lan.") {
return resultDone
}
host = strings.TrimSuffix(host, ".lan.")
s.tableHostToIPLock.Lock()
if s.tableHostToIP == nil {
s.tableHostToIPLock.Unlock()
return resultDone
}
ip, ok := s.tableHostToIP[host]
s.tableHostToIPLock.Unlock()
if !ok {
return resultDone
}
log.Debug("DNS: internal record: %s -> %s", req.Question[0].Name, ip.String())
resp := s.makeResponse(req)
if req.Question[0].Qtype == dns.TypeA {
a := &dns.A{}
a.Hdr = dns.RR_Header{
Name: req.Question[0].Name,
Rrtype: dns.TypeA,
Ttl: s.conf.BlockedResponseTTL,
Class: dns.ClassINET,
}
a.A = make([]byte, 4)
copy(a.A, ip)
resp.Answer = append(resp.Answer, a)
}
ctx.proxyCtx.Res = resp
return resultDone
}
// Respond to PTR requests if the target IP address is leased by our DHCP server
func processInternalIPAddrs(ctx *dnsContext) int {
s := ctx.srv
req := ctx.proxyCtx.Req
if req.Question[0].Qtype != dns.TypePTR {
return resultDone
}
arpa := req.Question[0].Name
arpa = strings.TrimSuffix(arpa, ".")
arpa = strings.ToLower(arpa)
ip := util.DNSUnreverseAddr(arpa)
if ip == nil {
return resultDone
}
s.tablePTRLock.Lock()
if s.tablePTR == nil {
s.tablePTRLock.Unlock()
return resultDone
}
host, ok := s.tablePTR[ip.String()]
s.tablePTRLock.Unlock()
if !ok {
return resultDone
}
log.Debug("DNS: reverse-lookup: %s -> %s", arpa, host)
resp := s.makeResponse(req)
ptr := &dns.PTR{}
ptr.Hdr = dns.RR_Header{
Name: req.Question[0].Name,
Rrtype: dns.TypePTR,
Ttl: s.conf.BlockedResponseTTL,
Class: dns.ClassINET,
}
ptr.Ptr = host + "."
resp.Answer = append(resp.Answer, ptr)
ctx.proxyCtx.Res = resp
return resultDone
}
// Apply filtering logic
func processFilteringBeforeRequest(ctx *dnsContext) int {
s := ctx.srv
d := ctx.proxyCtx
if d.Res != nil {
return resultDone // 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 {
ctx.setts = s.getClientRequestFilteringSettings(d)
ctx.result, err = s.filterDNSRequest(ctx)
}
s.RUnlock()
if err != nil {
ctx.err = err
return resultError
}
return resultDone
}
// Pass request to upstream servers; process the response
func processUpstream(ctx *dnsContext) int {
s := ctx.srv
d := ctx.proxyCtx
if d.Res != nil {
return resultDone // response is already set - nothing to do
}
if d.Addr != nil && s.conf.GetCustomUpstreamByClient != nil {
clientIP := ipFromAddr(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 resultError
}
ctx.responseFromUpstream = true
return resultDone
}
// Process DNSSEC after response from upstream server
func processDNSSECAfterResponse(ctx *dnsContext) int {
d := ctx.proxyCtx
if !ctx.responseFromUpstream || // don't process response if it's not from upstream servers
!ctx.srv.conf.EnableDNSSEC {
return resultDone
}
if !ctx.origReqDNSSEC {
optResp := d.Res.IsEdns0()
if optResp != nil && !optResp.Do() {
return resultDone
}
// 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 resultDone
}
// Apply filtering logic after we have received response from upstream servers
func processFilteringAfterResponse(ctx *dnsContext) int {
s := ctx.srv
d := ctx.proxyCtx
res := ctx.result
var err error
switch res.Reason {
case dnsfilter.ReasonRewrite:
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.genCNAMEAnswer(d.Req, res.CanonName))
answer = append(answer, d.Res.Answer...) // host -> IP
d.Res.Answer = answer
}
case dnsfilter.NotFilteredWhiteList:
// 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 resultError
}
if ctx.result != nil {
ctx.origResp = origResp2 // matched by response
} else {
ctx.result = &dnsfilter.Result{}
}
}
return resultDone
}