Fix recursion counter check. Add control to override depth of nested … (

google#4953)

* Fix recursion counter check. Add control to override depth of nested objects.

* Change if-condition to `>=`

CMakeLists.txt

@@ -23,6 +23,12 @@ if(NOT FLATBUFFERS_BUILD_FLATC AND FLATBUFFERS_BUILD_TESTS)
     set(FLATBUFFERS_BUILD_TESTS OFF)
 endif()
 
+if(DEFINED FLATBUFFERS_MAX_PARSING_DEPTH)
+  # Override the default recursion depth limit.
+  add_definitions(-DFLATBUFFERS_MAX_PARSING_DEPTH=${FLATBUFFERS_MAX_PARSING_DEPTH})
+  message(STATUS "FLATBUFFERS_MAX_PARSING_DEPTH: ${FLATBUFFERS_MAX_PARSING_DEPTH}")
+endif()
+
 set(FlatBuffers_Library_SRCS
   include/flatbuffers/code_generators.h
   include/flatbuffers/base.h

docs/source/Building.md

@@ -80,6 +80,14 @@ target_link_libraries(own_project_target PRIVATE flatbuffers)
 When build your project the `flatbuffers` library will be compiled and linked 
 to a target as part of your project.
 
+#### Override default depth limit of nested objects
+To override [the depth limit of recursion](@ref flatbuffers_guide_use_cpp), 
+add this directive:
+```cmake
+set(FLATBUFFERS_MAX_PARSING_DEPTH 16)
+```
+to `CMakeLists.txt` file before `add_subdirectory(${FLATBUFFERS_SRC_DIR})` line.
+
 #### For Google Play apps
 
 For applications on Google Play that integrate this library, usage is tracked.

docs/source/CppUsage.md

@@ -495,4 +495,13 @@ needed to use unions.
 
 To use scalars, simply wrap them in a struct.
 
+## Depth limit of nested objects and stack-overflow control
+The parser of Flatbuffers schema or json-files is kind of recursive parser.
+To avoid stack-overflow problem the parser has a built-in limiter of recursion depth.
+Number of nested declarations in a schema or number of nested json-objects is limited. 
+By default, this depth limit set to `64`.
+It is possible to override this limit with `FLATBUFFERS_MAX_PARSING_DEPTH` definition.
+This definition can be helpful for testing purposes or embedded applications.
+For details see [build](@ref flatbuffers_guide_building) of CMake-based projects.
+
 <br>

include/flatbuffers/idl.h

@@ -34,6 +34,12 @@
 // This file defines the data types representing a parsed IDL (Interface
 // Definition Language) / schema file.
 
+// Limits maximum depth of nested objects.
+// Prevents stack overflow while parse flatbuffers or json.
+#if !defined(FLATBUFFERS_MAX_PARSING_DEPTH)
+#  define FLATBUFFERS_MAX_PARSING_DEPTH 64
+#endif
+
 namespace flatbuffers {
 
 // The order of these matters for Is*() functions below.
@@ -745,10 +751,11 @@ class Parser : public ParserState {
   bool SupportsVectorOfUnions() const;
   Namespace *UniqueNamespace(Namespace *ns);
 
-  enum { kMaxParsingDepth = 64 };
   FLATBUFFERS_CHECKED_ERROR RecurseError();
   template<typename F> CheckedError Recurse(F f) {
-    if (++recurse_protection_counter >= kMaxParsingDepth) return RecurseError();
+    if (recurse_protection_counter >= (FLATBUFFERS_MAX_PARSING_DEPTH))
+      return RecurseError();
+    recurse_protection_counter++;
     auto ce = f();
     recurse_protection_counter--;
     return ce;

src/idl_parser.cpp

@@ -115,8 +115,8 @@ CheckedError Parser::Error(const std::string &msg) {
 inline CheckedError NoError() { return CheckedError(false); }
 
 CheckedError Parser::RecurseError() {
-  return Error("maximum parsing recursion of " + NumToString(kMaxParsingDepth) +
-               " reached");
+  return Error("maximum parsing recursion of " +
+               NumToString(FLATBUFFERS_MAX_PARSING_DEPTH) + " reached");
 }
 
 inline std::string OutOfRangeErrorMsg(int64_t val, const std::string &op,
@@ -2254,7 +2254,10 @@ bool Parser::ParseFlexBuffer(const char *source, const char *source_filename,
 
 bool Parser::Parse(const char *source, const char **include_paths,
                    const char *source_filename) {
-  return !ParseRoot(source, include_paths, source_filename).Check();
+  FLATBUFFERS_ASSERT(0 == recurse_protection_counter);
+  auto r = !ParseRoot(source, include_paths, source_filename).Check();
+  FLATBUFFERS_ASSERT(0 == recurse_protection_counter);
+  return r;
 }
 
 CheckedError Parser::StartParseFile(const char *source,