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/lua/luar.go

@@ -1,6 +1,9 @@
 package lua
 
 import (
+	"net"
+	"reflect"
+
 	glua "github.com/yuin/gopher-lua"
 	luar "layeh.com/gopher-luar"
 )
@@ -9,7 +12,7 @@ import (
 // The returned function wraps slices without reflection or metatable lookup,
 // and pushes nil for nil slices. Use it with this state or its coroutines.
 func NewSlicePusher[T any](L *glua.LState) func(*glua.LState, []T) {
-	metatable := luar.New(L, []T{}).(*glua.LUserData).Metatable
+	metatable := luar.MT(L, []T(nil)).LTable
 	return func(L *glua.LState, values []T) {
 		if values == nil {
 			L.Push(glua.LNil)
@@ -22,21 +25,105 @@ func NewSlicePusher[T any](L *glua.LState) func(*glua.LState, []T) {
 	}
 }
 
+// NewReadOnlySlicePusher borrows slices without copying and recursively makes
+// nested slice types read-only through their shared metatables. IP byte views
+// and masks are also read-only. Other referenced elements retain their mutability.
+// Element bindings are initialized on first indexing or iteration.
+func NewReadOnlySlicePusher[T any](L *glua.LState) func(*glua.LState, []T) {
+	sliceMetatable := luar.MT(L, []T{})
+	if sliceMetatable.RawGetString("__readonly") != glua.LTrue {
+		readOnly := L.NewFunction(func(L *glua.LState) int {
+			L.RaiseError("slice is read-only")
+			return 0
+		})
+		setSliceReadOnly[[]T](L, readOnly)
+	}
+	return NewSlicePusher[T](L)
+}
+
+func setSliceReadOnly[S ~[]E, E any](L *glua.LState, readOnly *glua.LFunction) {
+	var visit func(reflect.Type)
+	visit = func(typ reflect.Type) {
+		if typ.Kind() != reflect.Slice {
+			return
+		}
+		metatable := luar.MT(L, reflect.Zero(typ).Interface())
+		if metatable.RawGetString("__readonly") == glua.LTrue {
+			return
+		}
+		// Mark before descending because named slice types can be recursive.
+		metatable.RawSetString("__readonly", glua.LTrue)
+		metatable.RawSetString("__newindex", readOnly)
+		// Reject explicitly so Lua cannot fall back to the other operand.
+		metatable.RawSetString("__add", readOnly)
+		if typ == reflect.TypeFor[net.IP]() {
+			// A nil receiver lets AppendText return its argument as a writable []byte.
+			methods := metatable.RawGetString("methods").(*glua.LTable)
+			appendText := methods.RawGetString("AppendText")
+			for key, method := methods.Next(glua.LNil); key != glua.LNil; key, method = methods.Next(key) {
+				if method == appendText {
+					methods.RawSet(key, glua.LNil)
+				}
+			}
+			visit(reflect.TypeFor[net.IPMask]())
+		}
+		if element := typ.Elem(); element.Kind() == reflect.Slice {
+			index := metatable.RawGetString("__index").(*glua.LFunction)
+			call := metatable.RawGetString("__call").(*glua.LFunction)
+			initialize := func() {
+				visit(element)
+				metatable.RawSetString("__index", index)
+				metatable.RawSetString("__call", call)
+			}
+			metatable.RawSetString("__index", L.NewFunction(func(L *glua.LState) int {
+				initialize()
+				return index.GFunction(L)
+			}))
+			metatable.RawSetString("__call", L.NewFunction(func(L *glua.LState) int {
+				initialize()
+				return call.GFunction(L)
+			}))
+		}
+	}
+	visit(reflect.TypeFor[S]())
+}
+
 // DirectMethod handles a Lua call without luar's reflected method invocation.
 // It returns the result count and whether it handled the arguments. On false,
 // it must leave the stack unchanged for the original luar wrapper.
 type DirectMethod func(L *glua.LState) (nresults int, handled bool)
 
+// PushMethods pushes a luar userdata exposing only the named Go methods and
+// their aliases through reflected calls. The method list is fixed by the first
+// binding of that Go type in each LState.
+func PushMethods(L *glua.LState, value any, methods ...string) {
+	PushWithDirectMethods(L, value, nil, methods...)
+}
+
 // PushWithDirectMethods pushes a luar userdata with typed Go method bindings.
 // Handled calls bypass luar's argument conversion and reflect.Call; method lookup
 // uses the methods table directly instead of luar's reflected __index handler.
-// value must expose methods only. Bindings and their closures are installed once
-// per Go type per LState, outside the method-call hot path.
-func PushWithDirectMethods(L *glua.LState, value any, directMethods map[string]DirectMethod) {
+// Only directMethods and additionalMethods are exposed, including their aliases.
+// Bindings and their closures are installed once per Go type per LState, outside
+// the method-call hot path.
+func PushWithDirectMethods(L *glua.LState, value any, directMethods map[string]DirectMethod, additionalMethods ...string) {
 	userdata := luar.New(L, value).(*glua.LUserData)
 	metatable := userdata.Metatable.(*glua.LTable)
 	methods := metatable.RawGetString("methods").(*glua.LTable)
 	if metatable.RawGetString("__index") != methods {
+		// Keep all aliases for the explicitly exposed methods.
+		exposed := make(map[glua.LValue]bool, len(directMethods)+len(additionalMethods))
+		for name := range directMethods {
+			exposed[methods.RawGetString(name)] = true
+		}
+		for _, name := range additionalMethods {
+			exposed[methods.RawGetString(name)] = true
+		}
+		for key, method := methods.Next(glua.LNil); key != glua.LNil; key, method = methods.Next(key) {
+			if !exposed[method] {
+				methods.RawSet(key, glua.LNil)
+			}
+		}
 		for name, direct := range directMethods {
 			original := methods.RawGetString(name)
 			fn := L.NewFunction(func(L *glua.LState) int {
@@ -52,6 +139,10 @@ func PushWithDirectMethods(L *glua.LState, value any, directMethods map[string]D
 				}
 			}
 		}
+		// Pointer operations would bypass the method-only API.
+		metatable.RawSetString("__newindex", glua.LNil)
+		metatable.RawSetString("__pow", glua.LNil)
+		metatable.RawSetString("__unm", glua.LNil)
 		metatable.RawSetString("__index", methods)
 	}
 	L.Push(userdata)