Cap Recursion Depth in the Plugin JSON Converters

src/slic3r/plugin/PluginFsUtils.hpp

@@ -25,11 +25,19 @@ extern const char* const INSTALL_STATE_FILE;
 // Plugin config and orca.host.ui payloads both cross the boundary as plain JSON-compatible
 // values, so both go through these.
 
-inline pybind11::object json_to_py(const nlohmann::json& j)
+// Maximum nesting depth for JSON <-> Python conversion. A self-referential or pathologically
+// deep value would otherwise recurse until the native C stack overflows, an uncatchable crash;
+// past this bound we raise instead. 200 is far beyond any legitimate plugin config or UI payload.
+inline constexpr int kMaxJsonConversionDepth = 200;
+
+inline pybind11::object json_to_py(const nlohmann::json& j, int depth = 0)
 {
     namespace py = pybind11;
     using json   = nlohmann::json;
 
+    if (depth > kMaxJsonConversionDepth)
+        throw py::value_error("Plugin JSON value nested too deeply");
+
     switch (j.type()) {
     case json::value_t::null:            return py::none();
     case json::value_t::boolean:         return py::bool_(j.get<bool>());
@@ -40,24 +48,27 @@ inline pybind11::object json_to_py(const nlohmann::json& j)
     case json::value_t::array: {
         py::list lst;
         for (const auto& e : j)
-            lst.append(json_to_py(e));
+            lst.append(json_to_py(e, depth + 1));
         return lst;
     }
     case json::value_t::object: {
         py::dict d;
         for (auto it = j.begin(); it != j.end(); ++it)
-            d[py::str(it.key())] = json_to_py(it.value());
+            d[py::str(it.key())] = json_to_py(it.value(), depth + 1);
         return d;
     }
     default: return py::none();
     }
 }
 
-inline nlohmann::json py_to_json(const pybind11::handle& o)
+inline nlohmann::json py_to_json(const pybind11::handle& o, int depth = 0)
 {
     namespace py = pybind11;
     using json   = nlohmann::json;
 
+    if (depth > kMaxJsonConversionDepth)
+        throw py::value_error("Plugin value nested too deeply (possible cycle)");
+
     if (o.is_none())
         return json(nullptr);
     if (py::isinstance<py::bool_>(o)) // bool before int (bool subclasses int in Python)
@@ -73,13 +84,13 @@ inline nlohmann::json py_to_json(const pybind11::handle& o)
     if (py::isinstance<py::dict>(o)) {
         json obj = json::object();
         for (auto item : py::reinterpret_borrow<py::dict>(o))
-            obj[py::str(item.first).cast<std::string>()] = py_to_json(item.second);
+            obj[py::str(item.first).cast<std::string>()] = py_to_json(item.second, depth + 1);
         return obj;
     }
     if (py::isinstance<py::list>(o) || py::isinstance<py::tuple>(o)) {
         json arr = json::array();
         for (auto e : o)
-            arr.push_back(py_to_json(e));
+            arr.push_back(py_to_json(e, depth + 1));
         return arr;
     }
     return py::str(o).cast<std::string>(); // fallback: str()

tests/slic3rutils/CMakeLists.txt

@@ -34,6 +34,7 @@ add_executable(${_TEST_NAME}_tests
     test_plugin_sort.cpp
     test_plugin_cloud_metadata.cpp
     test_plugin_audit.cpp
+    test_plugin_json_depth.cpp
     test_shortcuts.cpp
     test_file_url.cpp
     test_user_manager.cpp

tests/slic3rutils/test_plugin_json_depth.cpp

@@ -0,0 +1,70 @@
+#include <catch2/catch_all.hpp>
+#include <catch2/catch_test_macros.hpp>
+
+#include <slic3r/plugin/PluginFsUtils.hpp>
+#include <slic3r/plugin/PluginManager.hpp>
+#include <slic3r/plugin/PythonInterpreter.hpp>
+
+#include "plugin_test_utils.hpp"
+
+#include <exception>
+#include <nlohmann/json.hpp>
+#include <pybind11/embed.h>
+#include <pybind11/gil.h>
+#include <pybind11/pytypes.h>
+
+using namespace Slic3r;
+
+namespace {
+// Brings the embedded interpreter up for one test and tears it down before boost::log does,
+// mirroring the ScopedPluginManager idiom in the other plugin tests.
+struct ScopedPluginManager
+{
+    ScopedDataDir python_data_dir{"plugin-json-depth"};
+    bool          initialized = PluginManager::instance().initialize();
+    ~ScopedPluginManager()
+    {
+        PluginManager::instance().shutdown();
+        PythonInterpreter::instance().shutdown();
+    }
+};
+} // namespace
+
+TEST_CASE("py_to_json raises instead of overflowing on pathologically deep input", "[PluginHost][Python]")
+{
+    ScopedPluginManager manager;
+    REQUIRE(manager.initialized);
+    namespace py = pybind11;
+    py::gil_scoped_acquire gil;
+
+    // [[[ ... 0 ... ]]] nested 300 deep: past the 200 conversion-depth cap, but shallow enough
+    // that the pre-fix code returns without crashing, so a regression fails cleanly rather than
+    // taking the process down. Built in C++ so the test does not depend on Python builtins.
+    py::object deep = py::int_(0);
+    for (int i = 0; i < 300; ++i) {
+        py::list wrapper;
+        wrapper.append(deep);
+        deep = std::move(wrapper);
+    }
+    CHECK_THROWS_AS(py_to_json(deep), std::exception);
+}
+
+TEST_CASE("py_to_json still converts reasonably nested input", "[PluginHost][Python]")
+{
+    ScopedPluginManager manager;
+    REQUIRE(manager.initialized);
+    namespace py = pybind11;
+    py::gil_scoped_acquire gil;
+
+    py::dict d;
+    d["a"] = py::int_(1);
+    py::list inner;
+    inner.append(py::str("x"));
+    inner.append(py::int_(2));
+    d["b"] = inner;
+
+    const nlohmann::json j = py_to_json(d);
+    CHECK(j.at("a").get<std::int64_t>() == 1);
+    CHECK(j.at("b").at(0).get<std::string>() == "x");
+    CHECK(j.at("b").at(1).get<std::int64_t>() == 2);
+}