feat: use dns question flipping trick to reduce dns pollution

component/control/dns.go

@@ -6,11 +6,14 @@
 package control
 
 import (
+	"encoding/binary"
 	"fmt"
 	"github.com/cilium/ebpf"
 	"github.com/v2rayA/dae/common"
 	"github.com/v2rayA/dae/common/consts"
 	"golang.org/x/net/dns/dnsmessage"
+	"hash/fnv"
+	"math/rand"
 	"net/netip"
 	"strings"
 	"time"
@@ -96,13 +99,39 @@ func (c *ControlPlane) LookupDnsRespCache(msg *dnsmessage.Message) (resp []byte)
 	return nil
 }
 
+// FlipDnsQuestionCase is used to reduce dns pollution.
+func FlipDnsQuestionCase(dm *dnsmessage.Message) {
+	if len(dm.Questions) == 0 {
+		return
+	}
+	q := &dm.Questions[0]
+	// For reproducibility, we use dm.ID as input and add some entropy to make the results more discrete.
+	h := fnv.New64()
+	var buf [4]byte
+	binary.BigEndian.PutUint16(buf[:], dm.ID)
+	h.Write(buf[:2])
+	binary.BigEndian.PutUint32(buf[:], 20230204) // entropy
+	h.Write(buf[:])
+	r := rand.New(rand.NewSource(int64(h.Sum64())))
+	perm := r.Perm(int(q.Name.Length))
+	for i := 0; i < int(q.Name.Length/3); i++ {
+		j := perm[i]
+		// Upper to lower; lower to upper.
+		if q.Name.Data[j] >= 'a' && q.Name.Data[j] <= 'z' {
+			q.Name.Data[j] -= 'a' - 'A'
+		} else if q.Name.Data[j] >= 'A' && q.Name.Data[j] <= 'Z' {
+			q.Name.Data[j] += 'a' - 'A'
+		}
+	}
+}
+
 // DnsRespHandler handle DNS resp. This function should be invoked when cache miss.
 func (c *ControlPlane) DnsRespHandler(data []byte) (newData []byte, err error) {
 	var msg dnsmessage.Message
 	if err = msg.Unpack(data); err != nil {
 		return nil, fmt.Errorf("unpack dns pkt: %w", err)
 	}
-
+	FlipDnsQuestionCase(&msg)
 	// Check healthy.
 	if !msg.Response || msg.RCode != dnsmessage.RCodeSuccess || len(msg.Questions) == 0 {
 		return data, nil
@@ -140,8 +169,8 @@ func (c *ControlPlane) DnsRespHandler(data []byte) (newData []byte, err error) {
 
 	// Update dnsCache.
 	c.mutex.Lock()
-	fqdn := q.Name.String()
+	fqdn := strings.ToLower(q.Name.String())
-	cacheKey := strings.ToLower(fqdn) + q.Type.String()
+	cacheKey := fqdn + q.Type.String()
 	cache, ok := c.dnsCache[cacheKey]
 	if ok {
 		c.mutex.Unlock()

component/control/udp.go

@@ -15,6 +15,7 @@ import (
 	"golang.org/x/net/dns/dnsmessage"
 	"net"
 	"net/netip"
+	"strings"
 	"time"
 )
 
@@ -122,7 +123,7 @@ func (c *ControlPlane) handlePkt(data []byte, lConn *net.UDPConn, lAddrPort neti
 			if c.log.IsLevelEnabled(logrus.DebugLevel) && len(dnsMessage.Questions) > 0 {
 				q := dnsMessage.Questions[0]
 				c.log.Tracef("UDP(DNS) %v <-[%v]-> Cache: %v %v",
-					RefineSourceToShow(lAddrPort, dest.Addr()), outbound.Name, q.Name, q.Type,
+					RefineSourceToShow(lAddrPort, dest.Addr()), outbound.Name, strings.ToLower(q.Name.String()), q.Type,
 				)
 			}
 			return nil
@@ -132,6 +133,12 @@ func (c *ControlPlane) handlePkt(data []byte, lConn *net.UDPConn, lAddrPort neti
 			// NOTICE: Routing was calculated in advance by the eBPF program.
 			dummyFrom = &addrHdr.Dest
 			dest = c.dnsUpstream
+
+			// Flip dns question to reduce dns pollution.
+			FlipDnsQuestionCase(dnsMessage)
+			if data, err = dnsMessage.Pack(); err != nil {
+				return fmt.Errorf("pack flipped dns packet: %w", err)
+			}
 		}
 	}
 
@@ -159,7 +166,7 @@ func (c *ControlPlane) handlePkt(data []byte, lConn *net.UDPConn, lAddrPort neti
 			"l4proto":  "UDP(DNS)",
 			"outbound": outbound.Name,
 			"dialer":   d.Name(),
-			"qname":    q.Name,
+			"qname":    strings.ToLower(q.Name.String()),
 			"qtype":    q.Type,
 		}).Infof("%v <-> %v",
 			RefineSourceToShow(lAddrPort, dest.Addr()), RefineAddrPortToShow(dest),

example.dae

@@ -9,7 +9,7 @@ global {
     # Now only support UDP and IP:Port.
     # Please make sure DNS traffic will go through and be forwarded by dae.
     # The request to dns upstream follows routing defined below.
-    dns_upstream: '1.1.1.1:53'
+    dns_upstream: '8.8.8.8:53'
 
     # The LAN interface to bind. Use it if you only want to proxy LAN instead of localhost.
     # Multiple interfaces split by ",".
@@ -62,7 +62,7 @@ group {
 routing {
     # See routing.md for full examples.
 
-    ip(1.1.1.1) && port(53) -> my_group
+    pname(dae) && ip(8.8.8.8) && port(53) -> direct
 
     pname(firefox) && domain(ip.sb) -> direct
     pname(curl) && domain(ip.sb) -> my_group