Finalmask: Fix unexpected order and UDP's buf issue (#6331)

XTLS/Xray-docs-next#866 (comment)

And #6331 (comment)

Fixes #6184 (comment)

Author: LjhAUMEM

infra/conf/transport_internet.go

@@ -1788,12 +1788,15 @@ func (c *MkcpLegacy) Build() (proto.Message, error) {
 }
 
 type Salamander struct {
-	Password   string      `json:"password"`
-	PacketSize *Int32Range `json:"packetSize"`
+	Password   string     `json:"password"`
+	PacketSize Int32Range `json:"packetSize"`
 }
 
 func (c *Salamander) Build() (proto.Message, error) {
-	if c.PacketSize != nil {
+	if c.PacketSize.To > 0 {
+		if c.PacketSize.From <= 0 || c.PacketSize.To > 2048 {
+			return nil, errors.New("gecko: invalid min/max packet size")
+		}
 		return &salamander.GeckoConfig{
 			Password:      c.Password,
 			MinPacketSize: c.PacketSize.From,

transport/internet/finalmask/finalmask.go

@@ -3,6 +3,7 @@ package finalmask
 import (
 	"context"
 	"net"
+	"slices"
 
 	"github.com/xtls/xray-core/common/buf"
 	"github.com/xtls/xray-core/common/errors"
@@ -28,7 +29,7 @@ func NewUdpmaskManager(udpmasks []Udpmask) *UdpmaskManager {
 func (m *UdpmaskManager) WrapPacketConnClient(raw net.PacketConn) (net.PacketConn, error) {
 	var sizes []int
 	var conns []net.PacketConn
-	for i, mask := range m.udpmasks {
+	for i, mask := range slices.Backward(m.udpmasks) {
 		if _, ok := mask.(headerConn); ok {
 			conn, err := mask.WrapPacketConnClient(nil, i, len(m.udpmasks)-1)
 			if err != nil {
@@ -61,7 +62,7 @@ func (m *UdpmaskManager) WrapPacketConnClient(raw net.PacketConn) (net.PacketCon
 func (m *UdpmaskManager) WrapPacketConnServer(raw net.PacketConn) (net.PacketConn, error) {
 	var sizes []int
 	var conns []net.PacketConn
-	for i, mask := range m.udpmasks {
+	for i, mask := range slices.Backward(m.udpmasks) {
 		if _, ok := mask.(headerConn); ok {
 			conn, err := mask.WrapPacketConnServer(nil, i, len(m.udpmasks)-1)
 			if err != nil {
@@ -124,32 +125,32 @@ func (c *headerManagerConn) ReadFrom(p []byte) (n int, addr net.Addr, err error)
 		if err != nil {
 			return n, addr, err
 		}
-		b = b[:n]
+		buf := b[:n]
 
 		sum := 0
 		for _, size := range c.sizes {
 			sum += size
 		}
 
 		if n < sum {
-			errors.LogError(context.Background(), "[mask] drop packet from ", addr, " with size ", len(b))
+			errors.LogError(context.Background(), "[mask] drop packet from ", addr, " with size ", n)
 			continue
 		}
 
 		for i := range c.conns {
-			n, _, err = c.conns[i].ReadFrom(b)
+			n, _, err = c.conns[i].ReadFrom(buf)
 			if err != nil {
-				errors.LogErrorInner(context.Background(), err, "[mask] drop packet from ", addr, " with size ", len(b))
+				errors.LogErrorInner(context.Background(), err, "[mask] drop packet from ", addr, " with size ", n)
 				break
 			}
-			b = b[c.sizes[i] : n+c.sizes[i]]
+			buf = buf[c.sizes[i] : n+c.sizes[i]]
 		}
 
 		if err != nil {
 			continue
 		}
 
-		return copy(p, b), addr, nil
+		return copy(p, buf), addr, nil
 	}
 }
 
@@ -212,7 +213,7 @@ func NewTcpmaskManager(tcpmasks []Tcpmask) *TcpmaskManager {
 
 func (m *TcpmaskManager) WrapConnClient(raw net.Conn) (net.Conn, error) {
 	var err error
-	for _, mask := range m.tcpmasks {
+	for _, mask := range slices.Backward(m.tcpmasks) {
 		raw, err = mask.WrapConnClient(raw)
 		if err != nil {
 			return nil, err
@@ -223,7 +224,7 @@ func (m *TcpmaskManager) WrapConnClient(raw net.Conn) (net.Conn, error) {
 
 func (m *TcpmaskManager) WrapConnServer(raw net.Conn) (net.Conn, error) {
 	var err error
-	for _, mask := range m.tcpmasks {
+	for _, mask := range slices.Backward(m.tcpmasks) {
 		raw, err = mask.WrapConnServer(raw)
 		if err != nil {
 			return nil, err