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filter.go
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filter.go
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package dnsforward
import (
"encoding/binary"
"fmt"
"strings"
"github.com/AdguardTeam/AdGuardHome/internal/filtering"
"github.com/AdguardTeam/dnsproxy/proxy"
"github.com/AdguardTeam/golibs/log"
"github.com/AdguardTeam/golibs/netutil"
"github.com/miekg/dns"
)
// beforeRequestHandler is the handler that is called before any other
// processing, including logs. It performs access checks and puts the client
// ID, if there is one, into the server's cache.
func (s *Server) beforeRequestHandler(
_ *proxy.Proxy,
pctx *proxy.DNSContext,
) (reply bool, err error) {
clientID, err := s.clientIDFromDNSContext(pctx)
if err != nil {
return false, fmt.Errorf("getting clientid: %w", err)
}
addrPort := netutil.NetAddrToAddrPort(pctx.Addr)
blocked, _ := s.IsBlockedClient(addrPort.Addr(), clientID)
if blocked {
return s.preBlockedResponse(pctx)
}
if len(pctx.Req.Question) == 1 {
host := strings.TrimSuffix(pctx.Req.Question[0].Name, ".")
if s.access.isBlockedHost(host) {
log.Debug("host %s is in access blocklist", host)
return s.preBlockedResponse(pctx)
}
}
if clientID != "" {
key := [8]byte{}
binary.BigEndian.PutUint64(key[:], pctx.RequestID)
s.clientIDCache.Set(key[:], []byte(clientID))
}
return true, nil
}
// getClientRequestFilteringSettings looks up client filtering settings using
// the client's IP address and ID, if any, from dctx.
func (s *Server) getClientRequestFilteringSettings(dctx *dnsContext) *filtering.Settings {
setts := s.dnsFilter.GetConfig()
setts.ProtectionEnabled = dctx.protectionEnabled
if s.conf.FilterHandler != nil {
ip, _ := netutil.IPAndPortFromAddr(dctx.proxyCtx.Addr)
s.conf.FilterHandler(ip, dctx.clientID, &setts)
}
return &setts
}
// filterDNSRequest applies the dnsFilter and sets dctx.proxyCtx.Res if the
// request was filtered.
func (s *Server) filterDNSRequest(dctx *dnsContext) (res *filtering.Result, err error) {
pctx := dctx.proxyCtx
req := pctx.Req
q := req.Question[0]
host := strings.TrimSuffix(q.Name, ".")
resVal, err := s.dnsFilter.CheckHost(host, q.Qtype, dctx.setts)
if err != nil {
return nil, fmt.Errorf("checking host %q: %w", host, err)
}
// TODO(a.garipov): Make CheckHost return a pointer.
res = &resVal
switch {
case res.IsFiltered:
log.Tracef("host %q is filtered, reason %q, rule: %q", host, res.Reason, res.Rules[0].Text)
pctx.Res = s.genDNSFilterMessage(pctx, res)
case res.Reason.In(filtering.Rewritten, filtering.RewrittenRule) &&
res.CanonName != "" &&
len(res.IPList) == 0:
// Resolve the new canonical name, not the original host name. The
// original question is readded in processFilteringAfterResponse.
dctx.origQuestion = q
req.Question[0].Name = dns.Fqdn(res.CanonName)
case res.Reason == filtering.Rewritten:
pctx.Res = s.filterRewritten(req, host, res, q.Qtype)
case res.Reason.In(filtering.RewrittenRule, filtering.RewrittenAutoHosts):
if err = s.filterDNSRewrite(req, res, pctx); err != nil {
return nil, err
}
}
return res, err
}
// filterRewritten handles DNS rewrite filters. It returns a DNS response with
// the data from the filtering result. All parameters must not be nil.
func (s *Server) filterRewritten(
req *dns.Msg,
host string,
res *filtering.Result,
qt uint16,
) (resp *dns.Msg) {
resp = s.makeResponse(req)
name := host
if len(res.CanonName) != 0 {
resp.Answer = append(resp.Answer, s.genAnswerCNAME(req, res.CanonName))
name = res.CanonName
}
for _, ip := range res.IPList {
switch qt {
case dns.TypeA:
a := s.genAnswerA(req, ip.To4())
a.Hdr.Name = dns.Fqdn(name)
resp.Answer = append(resp.Answer, a)
case dns.TypeAAAA:
a := s.genAnswerAAAA(req, ip)
a.Hdr.Name = dns.Fqdn(name)
resp.Answer = append(resp.Answer, a)
}
}
return resp
}
// checkHostRules checks the host against filters. It is safe for concurrent
// use.
func (s *Server) checkHostRules(host string, rrtype uint16, setts *filtering.Settings) (
r *filtering.Result,
err error,
) {
s.serverLock.RLock()
defer s.serverLock.RUnlock()
if s.dnsFilter == nil {
return nil, nil
}
var res filtering.Result
res, err = s.dnsFilter.CheckHostRules(host, rrtype, setts)
if err != nil {
return nil, err
}
return &res, err
}
// filterDNSResponse checks each resource record of the response's answer
// section from pctx and returns a non-nil res if at least one of canonical
// names or IP addresses in it matches the filtering rules.
func (s *Server) filterDNSResponse(
pctx *proxy.DNSContext,
setts *filtering.Settings,
) (res *filtering.Result, err error) {
if !setts.FilteringEnabled {
return nil, nil
}
for _, a := range pctx.Res.Answer {
host := ""
var rrtype uint16
switch a := a.(type) {
case *dns.CNAME:
host = strings.TrimSuffix(a.Target, ".")
rrtype = dns.TypeCNAME
case *dns.A:
host = a.A.String()
rrtype = dns.TypeA
case *dns.AAAA:
host = a.AAAA.String()
rrtype = dns.TypeAAAA
default:
continue
}
log.Debug("dnsforward: checking %s %s for %s", dns.Type(rrtype), host, a.Header().Name)
res, err = s.checkHostRules(host, rrtype, setts)
if err != nil {
return nil, err
} else if res == nil {
continue
} else if res.IsFiltered {
pctx.Res = s.genDNSFilterMessage(pctx, res)
log.Debug("DNSFwd: Matched %s by response: %s", pctx.Req.Question[0].Name, host)
return res, nil
}
}
return nil, nil
}