DomainMatcher: Fix Match() result slice aliasing race (#5959)

Fixes https://github.com/XTLS/Xray-core/pull/5814

app/dns/dns.go

@@ -271,11 +271,11 @@ func (s *DNS) sortClients(domain string) []*Client {
 
 	// Priority domain matching
 	hasMatch := false
-	MatchSlice := s.domainMatcher.Match(strings.ToLower(domain))
-	sort.Slice(MatchSlice, func(i, j int) bool {
-		return MatchSlice[i] < MatchSlice[j]
+	matchSlice := s.domainMatcher.Match(strings.ToLower(domain))
+	sort.Slice(matchSlice, func(i, j int) bool {
+		return matchSlice[i] < matchSlice[j]
 	})
-	for _, match := range MatchSlice {
+	for _, match := range matchSlice {
 		info := s.matcherInfos[match]
 		client := s.clients[info.clientIdx]
 		domainRule := info.domainRule

common/geodata/domain_matcher.go

@@ -11,7 +11,11 @@ import (
 )
 
 type DomainMatcher interface {
+	// Match returns the indices of all rules that match the input domain.
+	// The returned slice is owned by the caller and may be safely modified.
+	// Note: the slice may contain duplicates and the order is unspecified.
 	Match(input string) []uint32
+
 	MatchAny(input string) bool
 }
 

common/geodata/domain_matcher_test.go

@@ -48,3 +48,25 @@ func TestCompactDomainMatcher_PreservesMixedRuleIndices(t *testing.T) {
 		t.Fatalf("Match() = %v, want %v", got, want)
 	}
 }
+
+func TestMphDomainMatcher_MatchReturnsDetachedSlice(t *testing.T) {
+	matcher, err := (&MphDomainMatcherFactory{}).BuildMatcher([]*DomainRule{
+		{Value: &DomainRule_Custom{Custom: &Domain{Type: Domain_Full, Value: "example.com"}}},
+		{Value: &DomainRule_Custom{Custom: &Domain{Type: Domain_Domain, Value: "example.com"}}},
+	})
+	if err != nil {
+		t.Fatalf("BuildMatcher() failed: %v", err)
+	}
+
+	got := matcher.Match("example.com")
+	if !reflect.DeepEqual(got, []uint32{0, 1}) {
+		t.Fatalf("Match() = %v, want %v", got, []uint32{0, 1})
+	}
+
+	got[0] = 1
+
+	gotAgain := matcher.Match("example.com")
+	if !reflect.DeepEqual(gotAgain, []uint32{0, 1}) {
+		t.Fatalf("Match() after caller mutation = %v, want %v", gotAgain, []uint32{0, 1})
+	}
+}

common/geodata/strmatcher/matchers.go

@@ -3,6 +3,7 @@ package strmatcher
 import (
 	"errors"
 	"regexp"
+	"slices"
 	"strings"
 	"unicode/utf8"
 
@@ -253,13 +254,12 @@ func AddMatcherToGroup(g MatcherGroup, matcher Matcher, value uint32) error {
 }
 
 // CompositeMatches flattens the matches slice to produce a single matched indices slice.
-// It is designed to avoid new memory allocation as possible.
 func CompositeMatches(matches [][]uint32) []uint32 {
 	switch len(matches) {
 	case 0:
 		return nil
 	case 1:
-		return matches[0]
+		return slices.Clone(matches[0])
 	default:
 		result := make([]uint32, 0, 5)
 		for i := 0; i < len(matches); i++ {

common/geodata/strmatcher/strmatcher.go

@@ -62,6 +62,7 @@ type IndexMatcher interface {
 	// Match returns the indices of all matchers that matches the input.
 	//   * Empty array is returned if no such matcher exists.
 	//   * The order of returned matchers should follow priority specification.
+	//   * The returned slice is owned by the caller and may be safely modified.
 	// Priority specification:
 	//   1. Priority between matcher types: full > domain > substr > regex.
 	//   2. Priority of same-priority matchers matching at same position: the early added takes precedence.
@@ -89,6 +90,7 @@ type ValueMatcher interface {
 	//   * Empty array is returned if no such matcher exists.
 	//   * The order of returned values should follow priority specification.
 	//   * Same value may appear multiple times if multiple matched matchers were added with that value.
+	//   * The returned slice is owned by the caller and may be safely modified.
 	// Priority specification:
 	//   1. Priority between matcher types: full > domain > substr > regex.
 	//   2. Priority of same-priority matchers matching at same position: the early added takes precedence.