GDScript: Add limit to call depth

The hard limit is set at 2048 depth which seems sensible between
legitimate recursive calls while still avoiding a crash because of a
stack overflow in most of the cases.

Note that it is still possible to reach the stack limit and get an
overflow before reaching a call depth. This is intended as a half-way
measure to stop crashing in most cases, since there's no reliable nor
portable way to check the amount of stack memory left.

3 files changed, 35 insertions, 1 deletions

diff --git a/modules/gdscript/gdscript.cpp b/modules/gdscript/gdscript.cpp
index a876229276..4a3bddb747 100644
--- a/modules/gdscript/gdscript.cpp
+++ b/modules/gdscript/gdscript.cpp
@@ -2563,7 +2563,7 @@ GDScriptLanguage::GDScriptLanguage() {
 	script_frame_time = 0;
 
 	_debug_call_stack_pos = 0;
-	int dmcs = GLOBAL_DEF(PropertyInfo(Variant::INT, "debug/settings/gdscript/max_call_stack", PROPERTY_HINT_RANGE, "1024,4096,1,or_greater"), 1024);
+	int dmcs = GLOBAL_DEF(PropertyInfo(Variant::INT, "debug/settings/gdscript/max_call_stack", PROPERTY_HINT_RANGE, "512," + itos(GDScriptFunction::MAX_CALL_DEPTH - 1) + ",1"), 1024);
 
 	if (EngineDebugger::is_active()) {
 		//debugging enabled!
diff --git a/modules/gdscript/gdscript_function.h b/modules/gdscript/gdscript_function.h
index f45c1f9577..2624fb8dd9 100644
--- a/modules/gdscript/gdscript_function.h
+++ b/modules/gdscript/gdscript_function.h
@@ -544,6 +544,8 @@ private:
 #endif
 
 public:
+	static constexpr int MAX_CALL_DEPTH = 2048; // Limit to try to avoid crash because of a stack overflow.
+
 	struct CallState {
 		GDScript *script = nullptr;
 		GDScriptInstance *instance = nullptr;
diff --git a/modules/gdscript/gdscript_vm.cpp b/modules/gdscript/gdscript_vm.cpp
index b99f5d2685..26eee142f2 100644
--- a/modules/gdscript/gdscript_vm.cpp
+++ b/modules/gdscript/gdscript_vm.cpp
@@ -456,6 +456,33 @@ Variant GDScriptFunction::call(GDScriptInstance *p_instance, const Variant **p_a
 
 	r_err.error = Callable::CallError::CALL_OK;
 
+	static thread_local int call_depth = 0;
+	if (unlikely(++call_depth > MAX_CALL_DEPTH)) {
+		call_depth--;
+#ifdef DEBUG_ENABLED
+		String err_file;
+		if (p_instance && ObjectDB::get_instance(p_instance->owner_id) != nullptr && p_instance->script->is_valid() && !p_instance->script->path.is_empty()) {
+			err_file = p_instance->script->path;
+		} else if (_script) {
+			err_file = _script->path;
+		}
+		if (err_file.is_empty()) {
+			err_file = "<built-in>";
+		}
+		String err_func = name;
+		if (p_instance && ObjectDB::get_instance(p_instance->owner_id) != nullptr && p_instance->script->is_valid() && !p_instance->script->name.is_empty()) {
+			err_func = p_instance->script->name + "." + err_func;
+		}
+		int err_line = _initial_line;
+		const char *err_text = "Stack overflow. Check for infinite recursion in your script.";
+		if (!GDScriptLanguage::get_singleton()->debug_break(err_text, false)) {
+			// Debugger break did not happen.
+			_err_print_error(err_func.utf8().get_data(), err_file.utf8().get_data(), err_line, err_text, false, ERR_HANDLER_SCRIPT);
+		}
+#endif
+		return _get_default_variant_for_data_type(return_type);
+	}
+
 	Variant retvalue;
 	Variant *stack = nullptr;
 	Variant **instruction_args = nullptr;
@@ -490,10 +517,12 @@ Variant GDScriptFunction::call(GDScriptInstance *p_instance, const Variant **p_a
 				r_err.error = Callable::CallError::CALL_ERROR_TOO_MANY_ARGUMENTS;
 				r_err.argument = _argument_count;
 
+				call_depth--;
 				return _get_default_variant_for_data_type(return_type);
 			} else if (p_argcount < _argument_count - _default_arg_count) {
 				r_err.error = Callable::CallError::CALL_ERROR_TOO_FEW_ARGUMENTS;
 				r_err.argument = _argument_count - _default_arg_count;
+				call_depth--;
 				return _get_default_variant_for_data_type(return_type);
 			} else {
 				defarg = _argument_count - p_argcount;
@@ -521,6 +550,7 @@ Variant GDScriptFunction::call(GDScriptInstance *p_instance, const Variant **p_a
 				r_err.error = Callable::CallError::CALL_ERROR_INVALID_ARGUMENT;
 				r_err.argument = i;
 				r_err.expected = argument_types[i].builtin_type;
+				call_depth--;
 				return _get_default_variant_for_data_type(return_type);
 			}
 			if (argument_types[i].kind == GDScriptDataType::BUILTIN) {
@@ -3570,5 +3600,7 @@ Variant GDScriptFunction::call(GDScriptInstance *p_instance, const Variant **p_a
 		stack[i].~Variant();
 	}
 
+	call_depth--;
+
 	return retvalue;
 }