Lua: Sandbox by default (whitelisted functions); Disable inline scripts for now; Add more checks for security reasons (#7136)

https://github.com/XTLS/Xray-core/pull/7136#issuecomment-6158632073
https://github.com/XTLS/Xray-core/pull/7136#issuecomment-6170831601
https://github.com/XTLS/Xray-core/pull/7136#issuecomment-6184362904

common/platform/filesystem/file.go

@@ -34,12 +34,13 @@ func ReadAsset(file string) ([]byte, error) {
 	return ReadFile(path)
 }
 
-func OpenAsset(file string) (io.ReadCloser, error) {
-	path, _, err := getAssetFileLocation(file)
+func OpenAsset(file string) (io.ReadCloser, int64, error) {
+	path, info, err := getAssetFileLocation(file)
 	if err != nil {
-		return nil, err
+		return nil, 0, err
 	}
-	return NewFileReader(path)
+	r, err := NewFileReader(path)
+	return r, info.Size(), err
 }
 
 func StatAsset(file string) (os.FileInfo, error) {

common/platform/platform.go

@@ -93,7 +93,7 @@ func GetConfDirPath() string {
 	return configPath
 }
 
-// ResolveLuaFile finds a local Lua script and returns its absolute path.
+// ResolveLuaFile finds a local .lua script and returns its resolved absolute path.
 // Relative paths: XRAY_LOCATION_CONFDIR > XRAY_LOCATION_CONFIG > working dir > executable dir.
 func ResolveLuaFile(path string) (string, error) {
 	if path == "" {
@@ -113,7 +113,22 @@ func ResolveLuaFile(path string) (string, error) {
 			}
 		}
 	}
-	return resolveFile(paths)
+	path, err := resolveFile(paths)
+	if err != nil {
+		return "", err
+	}
+	return resolveLuaTarget(path)
+}
+
+func resolveLuaTarget(path string) (string, error) {
+	path, err := filepath.EvalSymlinks(path)
+	if err != nil {
+		return "", fmt.Errorf("failed to resolve Lua file symlinks: %w", err)
+	}
+	if filepath.Ext(path) != ".lua" {
+		return "", errors.New("Lua file extension must be .lua")
+	}
+	return path, nil
 }
 
 func resolveFile(paths []string) (string, error) {

common/platform/platform_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"path/filepath"
 	"runtime"
+	"strings"
 	"testing"
 
 	"github.com/xtls/xray-core/common"
@@ -88,6 +89,10 @@ func TestResolveLuaFile(t *testing.T) {
 	for _, path := range paths[:3] {
 		common.Must(os.WriteFile(path, nil, 0o600))
 	}
+	for i, path := range paths {
+		paths[i], err = filepath.EvalSymlinks(path)
+		common.Must(err)
+	}
 	if got, err := ResolveLuaFile(paths[2]); err != nil || got != paths[2] {
 		t.Fatalf("absolute path = %q, %v; want %q", got, err, paths[2])
 	}
@@ -115,3 +120,35 @@ func TestResolveLuaFile(t *testing.T) {
 		}
 	}
 }
+
+func TestResolveLuaFileSymlink(t *testing.T) {
+	for _, tc := range []struct {
+		link, target string
+		valid        bool
+	}{
+		{"alias.lua", "data.dat", false},
+		{"alias.dat", "script.lua", true},
+	} {
+		t.Run(tc.link, func(t *testing.T) {
+			dir, err := filepath.EvalSymlinks(t.TempDir())
+			common.Must(err)
+			target := filepath.Join(dir, tc.target)
+			common.Must(os.WriteFile(target, nil, 0o600))
+			link := filepath.Join(dir, tc.link)
+			if err := os.Symlink(tc.target, link); err != nil {
+				if runtime.GOOS == "windows" {
+					t.Skipf("cannot create symlinks: %v", err)
+				}
+				t.Fatal(err)
+			}
+			got, err := ResolveLuaFile(link)
+			if tc.valid {
+				if err != nil || got != target {
+					t.Fatalf("ResolveLuaFile(%q) = %q, %v; want %q", link, got, err, target)
+				}
+			} else if err == nil || got != "" || !strings.Contains(err.Error(), "Lua file extension must be .lua") {
+				t.Fatalf("ResolveLuaFile(%q) = %q, %v; want .lua extension error", link, got, err)
+			}
+		})
+	}
+}