File loader: Check file extensions without resolving symlinks (#7255)

https://github.com/XTLS/Xray-core/pull/7255#issuecomment-6481194940
https://github.com/XTLS/Xray-core/pull/7250#issuecomment-6398816842

Fixes https://github.com/XTLS/Xray-core/issues/7239#issuecomment-6356122816

---------

Co-authored-by: Eljees <3.14hell@gmail.com>

common/platform/filesystem/file.go

@@ -5,6 +5,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/xtls/xray-core/common/buf"
 	"github.com/xtls/xray-core/common/platform"
@@ -26,14 +27,6 @@ func ReadFile(path string) ([]byte, error) {
 	return buf.ReadAllToBytes(reader)
 }
 
-func ReadAsset(file string) ([]byte, error) {
-	path, _, err := getAssetFileLocation(file)
-	if err != nil {
-		return nil, err
-	}
-	return ReadFile(path)
-}
-
 func OpenAsset(file string) (io.ReadCloser, int64, error) {
 	path, info, err := getAssetFileLocation(file)
 	if err != nil {
@@ -43,11 +36,6 @@ func OpenAsset(file string) (io.ReadCloser, int64, error) {
 	return r, info.Size(), err
 }
 
-func StatAsset(file string) (os.FileInfo, error) {
-	_, info, err := getAssetFileLocation(file)
-	return info, err
-}
-
 func ResolveAsset(file string) (string, error) {
 	path, _, err := getAssetFileLocation(file)
 	return path, err
@@ -79,17 +67,29 @@ func ReadCert(file string) ([]byte, error) {
 	return ReadFile(platform.GetCertLocation(file))
 }
 
-func CopyFile(dst string, src string) error {
-	bytes, err := ReadFile(src)
-	if err != nil {
-		return err
+// ResolveLuaFile finds a local .lua script and returns its absolute path.
+// Relative paths: XRAY_LOCATION_CONFDIR > XRAY_LOCATION_CONFIG > working dir > executable dir.
+func ResolveLuaFile(path string) (string, error) {
+	if !strings.EqualFold(filepath.Ext(path), ".lua") {
+		return "", errors.New("Lua file extension must be .lua")
 	}
-	f, err := os.OpenFile(dst, os.O_CREATE|os.O_WRONLY, 0o644)
-	if err != nil {
-		return err
+	if filepath.IsAbs(path) {
+		return path, nil
 	}
-	defer f.Close()
-
-	_, err = f.Write(bytes)
-	return err
+	for _, dir := range []string{
+		platform.GetConfDirPath(),
+		platform.NewEnvFlag(platform.ConfigLocation).GetValue(func() string { return "" }),
+		".",
+		platform.GetExecutableDir(),
+	} {
+		if dir != "" {
+			resolved := filepath.Join(dir, path)
+			if _, err := os.Stat(resolved); err == nil {
+				return filepath.Abs(resolved)
+			} else if !os.IsNotExist(err) {
+				return "", err
+			}
+		}
+	}
+	return "", os.ErrNotExist
 }

common/platform/filesystem/file_test.go

@@ -1,13 +1,17 @@
 package filesystem_test
 
 import (
+	"errors"
+	"os"
 	"path/filepath"
 	"testing"
 
+	"github.com/xtls/xray-core/common"
+	"github.com/xtls/xray-core/common/platform"
 	. "github.com/xtls/xray-core/common/platform/filesystem"
 )
 
-func TestStatAssetRejectsInvalidPath(t *testing.T) {
+func TestResolveAssetRejectsInvalidPath(t *testing.T) {
 	for _, file := range []string{
 		"",
 		".",
@@ -25,8 +29,49 @@ func TestStatAssetRejectsInvalidPath(t *testing.T) {
 		`nested\..\geoip.dat`,
 		filepath.Join(t.TempDir(), "geoip.dat"),
 	} {
-		if _, err := StatAsset(file); err == nil {
+		if _, err := ResolveAsset(file); err == nil {
 			t.Fatalf("expected error for %q", file)
 		}
 	}
 }
+
+func TestResolveLuaFile(t *testing.T) {
+	t.Chdir(t.TempDir())
+	workingDir, err := os.Getwd()
+	common.Must(err)
+	executable, err := os.Executable()
+	common.Must(err)
+	file, err := os.CreateTemp(filepath.Dir(executable), "lua-*.lua")
+	common.Must(err)
+	common.Must(file.Close())
+	defer os.Remove(file.Name())
+
+	name := filepath.Base(file.Name())
+	paths := []string{
+		filepath.Join(t.TempDir(), name),
+		filepath.Join(t.TempDir(), name),
+		filepath.Join(workingDir, name),
+		file.Name(),
+	}
+	t.Setenv(platform.ConfdirLocation, filepath.Dir(paths[0]))
+	t.Setenv(platform.ConfigLocation, filepath.Dir(paths[1]))
+	for _, path := range paths[:3] {
+		common.Must(os.WriteFile(path, nil, 0o600))
+	}
+	if got, err := ResolveLuaFile(paths[2]); err != nil || got != paths[2] {
+		t.Fatalf("absolute path = %q, %v; want %q", got, err, paths[2])
+	}
+	for i, want := range paths {
+		if i == 2 {
+			t.Setenv(platform.ConfdirLocation, "")
+			t.Setenv(platform.ConfigLocation, "")
+		}
+		if got, err := ResolveLuaFile(name); err != nil || got != want {
+			t.Fatalf("resolved path = %q, %v; want %q", got, err, want)
+		}
+		common.Must(os.Remove(want))
+	}
+	if _, err := ResolveLuaFile(name); !errors.Is(err, os.ErrNotExist) {
+		t.Fatalf("missing file error = %v", err)
+	}
+}