From 42524ba04e4851355c40e76df971abe2be2f538d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E4=B8=96=E7=95=8C?= <i@sekai.icu>
Date: Sat, 17 Sep 2022 16:53:40 +0800
Subject: [PATCH] Fix dns sniffer

---
 common/sniff/dns.go    | 4 ++++
 common/sniff/domain.go | 6 ------
 route/router.go        | 4 ++--
 3 files changed, 6 insertions(+), 8 deletions(-)
 delete mode 100644 common/sniff/domain.go

diff --git a/common/sniff/dns.go b/common/sniff/dns.go
index 9b2ad91f..d374e607 100644
--- a/common/sniff/dns.go
+++ b/common/sniff/dns.go
@@ -11,6 +11,7 @@ import (
 	C "github.com/sagernet/sing-box/constant"
 	"github.com/sagernet/sing/common"
 	"github.com/sagernet/sing/common/buf"
+	M "github.com/sagernet/sing/common/metadata"
 	"github.com/sagernet/sing/common/task"
 
 	mDNS "github.com/miekg/dns"
@@ -49,5 +50,8 @@ func DomainNameQuery(ctx context.Context, packet []byte) (*adapter.InboundContex
 	if err != nil {
 		return nil, err
 	}
+	if len(msg.Question) == 0 || msg.Question[0].Qclass != mDNS.ClassINET || !M.IsDomainName(msg.Question[0].Name) {
+		return nil, os.ErrInvalid
+	}
 	return &adapter.InboundContext{Protocol: C.ProtocolDNS}, nil
 }
diff --git a/common/sniff/domain.go b/common/sniff/domain.go
deleted file mode 100644
index 44021d3b..00000000
--- a/common/sniff/domain.go
+++ /dev/null
@@ -1,6 +0,0 @@
-package sniff
-
-import _ "unsafe" // for linkname
-
-//go:linkname IsDomainName net.isDomainName
-func IsDomainName(domain string) bool
diff --git a/route/router.go b/route/router.go
index ed4c5bf2..df975db3 100644
--- a/route/router.go
+++ b/route/router.go
@@ -554,7 +554,7 @@ func (r *Router) RouteConnection(ctx context.Context, conn net.Conn, metadata ad
 		if err == nil {
 			metadata.Protocol = sniffMetadata.Protocol
 			metadata.Domain = sniffMetadata.Domain
-			if metadata.SniffOverrideDestination && sniff.IsDomainName(metadata.Domain) {
+			if metadata.SniffOverrideDestination && M.IsDomainName(metadata.Domain) {
 				metadata.Destination = M.Socksaddr{
 					Fqdn: metadata.Domain,
 					Port: metadata.Destination.Port,
@@ -631,7 +631,7 @@ func (r *Router) RoutePacketConnection(ctx context.Context, conn N.PacketConn, m
 		if err == nil {
 			metadata.Protocol = sniffMetadata.Protocol
 			metadata.Domain = sniffMetadata.Domain
-			if metadata.SniffOverrideDestination && sniff.IsDomainName(metadata.Domain) {
+			if metadata.SniffOverrideDestination && M.IsDomainName(metadata.Domain) {
 				metadata.Destination = M.Socksaddr{
 					Fqdn: metadata.Domain,
 					Port: metadata.Destination.Port,