Harden v3 numeric parsing and add C fuzz harness

Reject non-finite/out-of-range JSON numbers in int32/uint64 fields and
array/attribute elements instead of silently truncating, initialize the
model on parse-file failure, and free the partial JSON document when the
root is not an object. Adds a pure-C libFuzzer harness (fuzz_gltf_v3_c)
alongside the existing C++ one and tests covering the new failure modes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/Makefile

@@ -5,3 +5,7 @@ all: ../tiny_gltf.h
 	clang++  -I../ $(EXTRA_CXXFLAGS) -std=c++11 -g -O0 -o tester tester.cc
 	clang++ -DTINYGLTF_NOEXCEPTION -I../ $(EXTRA_CXXFLAGS) -std=c++11 -g -O0 -o tester_noexcept tester.cc
 	clang++ -DTINYGLTF_USE_CUSTOM_JSON -I../ $(EXTRA_CXXFLAGS) -std=c++11 -g -O0 -o tester_intensive_customjson tester_intensive_customjson.cc
+	clang -I../ -std=c11 -g -O0 -o tester_v3_c tester_v3_c.c ../tiny_gltf_v3.c
+
+tester_v3_c: tester_v3_c.c ../tiny_gltf_v3.h ../tiny_gltf_v3.c ../tinygltf_json_c.h
+	clang -I../ -std=c11 -g -O0 -o tester_v3_c tester_v3_c.c ../tiny_gltf_v3.c

tests/tester_v3_c.c

@@ -129,6 +129,89 @@ static int check_minimal_write_roundtrip(void) {
   return 1;
 }
 
+static int check_parse_file_failure_initializes_model(void) {
+  tg3_model model;
+  tg3_error_stack errors;
+  tg3_parse_options opts;
+  tg3_error_code err;
+
+  memset(&model, 0xA5, sizeof(model));
+  tg3_error_stack_init(&errors);
+  tg3_parse_options_init(&opts);
+
+  err = tg3_parse_file(&model, &errors, "scene.gltf", 10, &opts);
+  if (err != TG3_ERR_FS_NOT_AVAILABLE) {
+    fprintf(stderr, "tg3_parse_file unexpected error: %d\n", (int)err);
+    tg3_error_stack_free(&errors);
+    return 0;
+  }
+
+  if (model.default_scene != -1) {
+    fprintf(stderr, "tg3_parse_file did not initialize model on failure\n");
+    tg3_model_free(&model);
+    tg3_error_stack_free(&errors);
+    return 0;
+  }
+
+  tg3_model_free(&model);
+  tg3_error_stack_free(&errors);
+  return 1;
+}
+
+static int check_non_object_root_rejected(void) {
+  static const uint8_t json[] = "\"not an object\"";
+  tg3_model model;
+  tg3_error_stack errors;
+  tg3_parse_options opts;
+  tg3_error_code err;
+
+  tg3_error_stack_init(&errors);
+  tg3_parse_options_init(&opts);
+
+  err = tg3_parse(&model, &errors, json, (uint64_t)(sizeof(json) - 1), "", 0, &opts);
+  if (err != TG3_ERR_JSON_PARSE) {
+    fprintf(stderr, "non-object root returned unexpected error: %d\n", (int)err);
+    tg3_model_free(&model);
+    tg3_error_stack_free(&errors);
+    return 0;
+  }
+
+  if (model.default_scene != -1) {
+    fprintf(stderr, "non-object root left model in unexpected state\n");
+    tg3_model_free(&model);
+    tg3_error_stack_free(&errors);
+    return 0;
+  }
+
+  tg3_model_free(&model);
+  tg3_error_stack_free(&errors);
+  return 1;
+}
+
+static int check_huge_integer_field_rejected(void) {
+  static const uint8_t json[] =
+      "{\"asset\":{\"version\":\"2.0\"},\"scene\":6.66667e+70}";
+  tg3_model model;
+  tg3_error_stack errors;
+  tg3_parse_options opts;
+  tg3_error_code err;
+
+  tg3_error_stack_init(&errors);
+  tg3_parse_options_init(&opts);
+
+  err = tg3_parse(&model, &errors, json, (uint64_t)(sizeof(json) - 1), "", 0, &opts);
+  if (err != TG3_ERR_JSON_PARSE) {
+    fprintf(stderr, "huge integer-like field returned unexpected error: %d\n", (int)err);
+    tg3_model_free(&model);
+    tg3_error_stack_free(&errors);
+    return 0;
+  }
+
+  tg3_model_free(&model);
+  tg3_error_stack_free(&errors);
+  return 1;
+}
+
 int main(void) {
   if (!check_minimal_parse()) {
     return 1;
@@ -136,5 +219,14 @@ int main(void) {
   if (!check_minimal_write_roundtrip()) {
     return 1;
   }
+  if (!check_parse_file_failure_initializes_model()) {
+    return 1;
+  }
+  if (!check_non_object_root_rejected()) {
+    return 1;
+  }
+  if (!check_huge_integer_field_rejected()) {
+    return 1;
+  }
   return 0;
 }

tests/v3/fuzzer/Makefile

@@ -1,19 +1,23 @@
-# tests/v3/fuzzer/Makefile — Build libFuzzer harness for tinygltf v3
+# tests/v3/fuzzer/Makefile — Build libFuzzer harnesses for tinygltf v3
 #
-# Requires: clang++ with libFuzzer support
+# Requires: clang/clang++ with libFuzzer support
 #
 # Targets:
-#   make             — build fuzzer with ASan + UBSan
-#   make run         — run fuzzer with default settings
+#   make             — build both harnesses with ASan + UBSan
+#   make run         — run the dedicated pure-C v3 harness
+#   make run-cpp     — run the legacy header-implementation harness
 #   make seed        — generate seed corpus from test models
 #   make clean       — remove binaries and corpus
 
+CC        = clang
 CXX       = clang++
+CCFLAGS   = -g -O1 -std=c11
 CXXFLAGS  = -g -O1 -std=c++17 -fno-rtti -fno-exceptions
 SANITIZE  = -fsanitize=fuzzer,address,undefined
 INCLUDES  = -I../../..
 
 FUZZER    = fuzz_gltf_v3
+FUZZER_C  = fuzz_gltf_v3_c
 CORPUS    = corpus
 ARTIFACTS = artifacts
 
@@ -21,16 +25,28 @@ ARTIFACTS = artifacts
 MAX_LEN   ?= 65536
 JOBS      ?= $(shell nproc 2>/dev/null || echo 4)
 MAX_TIME  ?= 0
+FUZZ_ENV  ?= LSAN_OPTIONS=detect_leaks=0
 
-.PHONY: all run seed clean
+.PHONY: all run run-cpp seed clean
 
-all: $(FUZZER)
+all: $(FUZZER) $(FUZZER_C)
 
 $(FUZZER): fuzz_gltf_v3.cc ../../../tiny_gltf_v3.h ../../../tiny_gltf_v3.c ../../../tinygltf_json_c.h
 	$(CXX) $(CXXFLAGS) $(SANITIZE) $(INCLUDES) -o $@ $<
 
-run: $(FUZZER) | $(CORPUS) $(ARTIFACTS)
-	./$(FUZZER) $(CORPUS) \
+$(FUZZER_C): fuzz_gltf_v3_c.c ../../../tiny_gltf_v3.h ../../../tiny_gltf_v3.c ../../../tinygltf_json_c.h
+	$(CC) $(CCFLAGS) $(SANITIZE) $(INCLUDES) -o $@ $< ../../../tiny_gltf_v3.c
+
+run: $(FUZZER_C) | $(CORPUS) $(ARTIFACTS)
+	$(FUZZ_ENV) ./$(FUZZER_C) $(CORPUS) \
+		-artifact_prefix=$(ARTIFACTS)/ \
+		-max_len=$(MAX_LEN) \
+		-jobs=$(JOBS) \
+		-workers=$(JOBS) \
+		$(if $(filter-out 0,$(MAX_TIME)),-max_total_time=$(MAX_TIME))
+
+run-cpp: $(FUZZER) | $(CORPUS) $(ARTIFACTS)
+	$(FUZZ_ENV) ./$(FUZZER) $(CORPUS) \
 		-artifact_prefix=$(ARTIFACTS)/ \
 		-max_len=$(MAX_LEN) \
 		-jobs=$(JOBS) \
@@ -63,5 +79,5 @@ $(ARTIFACTS):
 	mkdir -p $(ARTIFACTS)
 
 clean:
-	rm -f $(FUZZER)
+	rm -f $(FUZZER) $(FUZZER_C)
 	rm -rf $(CORPUS) $(ARTIFACTS)

tests/v3/fuzzer/fuzz_gltf_v3_c.c

@@ -0,0 +1,96 @@
+#include "tiny_gltf_v3.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+static const uint64_t FUZZ_MEMORY_BUDGET = 64ULL * 1024 * 1024;
+
+static void tg3_fuzz_parse_auto(const uint8_t *data, size_t size) {
+  tg3_model model;
+  tg3_error_stack errors;
+  tg3_parse_options opts;
+
+  tg3_error_stack_init(&errors);
+  tg3_parse_options_init(&opts);
+  opts.memory.memory_budget = FUZZ_MEMORY_BUDGET;
+
+  tg3_parse_auto(&model, &errors, data, (uint64_t)size, "", 0, &opts);
+
+  tg3_model_free(&model);
+  tg3_error_stack_free(&errors);
+}
+
+static void tg3_fuzz_parse_json(const uint8_t *data, size_t size) {
+  tg3_model model;
+  tg3_error_stack errors;
+  tg3_parse_options opts;
+
+  tg3_error_stack_init(&errors);
+  tg3_parse_options_init(&opts);
+  opts.memory.memory_budget = FUZZ_MEMORY_BUDGET;
+
+  tg3_parse(&model, &errors, data, (uint64_t)size, "", 0, &opts);
+
+  tg3_model_free(&model);
+  tg3_error_stack_free(&errors);
+}
+
+static void tg3_fuzz_parse_glb(const uint8_t *data, size_t size) {
+  tg3_model model;
+  tg3_error_stack errors;
+  tg3_parse_options opts;
+
+  tg3_error_stack_init(&errors);
+  tg3_parse_options_init(&opts);
+  opts.memory.memory_budget = FUZZ_MEMORY_BUDGET;
+
+  tg3_parse_glb(&model, &errors, data, (uint64_t)size, "", 0, &opts);
+
+  tg3_model_free(&model);
+  tg3_error_stack_free(&errors);
+}
+
+static void tg3_fuzz_parse_float32(const uint8_t *data, size_t size) {
+  tg3_model model;
+  tg3_error_stack errors;
+  tg3_parse_options opts;
+
+  tg3_error_stack_init(&errors);
+  tg3_parse_options_init(&opts);
+  opts.memory.memory_budget = FUZZ_MEMORY_BUDGET;
+  opts.parse_float32 = 1;
+
+  tg3_parse_auto(&model, &errors, data, (uint64_t)size, "", 0, &opts);
+
+  tg3_model_free(&model);
+  tg3_error_stack_free(&errors);
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  uint8_t selector;
+  const uint8_t *payload;
+  size_t payload_size;
+
+  if (size == 0) return 0;
+
+  selector = data[0] % 4;
+  payload = data + 1;
+  payload_size = size - 1;
+
+  switch (selector) {
+    case 0:
+      tg3_fuzz_parse_auto(payload, payload_size);
+      break;
+    case 1:
+      tg3_fuzz_parse_json(payload, payload_size);
+      break;
+    case 2:
+      tg3_fuzz_parse_glb(payload, payload_size);
+      break;
+    case 3:
+      tg3_fuzz_parse_float32(payload, payload_size);
+      break;
+  }
+
+  return 0;
+}

tiny_gltf_v3.c

@@ -451,6 +451,46 @@ static int tg3__json_is_number(const tg3json_value *v) {
     return v && (v->type == TG3JSON_INT || v->type == TG3JSON_REAL);
 }
 
+static int tg3__json_number_to_int32(const tg3json_value *v, int32_t *out) {
+    double real;
+    int32_t converted;
+    if (!tg3__json_is_number(v) || !out) return 0;
+    if (v->type == TG3JSON_INT) {
+        if (v->u.integer < INT32_MIN || v->u.integer > INT32_MAX) return 0;
+        *out = (int32_t)v->u.integer;
+        return 1;
+    }
+    real = v->u.real;
+    if (!isfinite(real) || real < (double)INT32_MIN || real > (double)INT32_MAX) {
+        return 0;
+    }
+    converted = (int32_t)real;
+    if ((double)converted != real) return 0;
+    *out = converted;
+    return 1;
+}
+
+static int tg3__json_number_to_uint64(const tg3json_value *v, uint64_t *out) {
+    double real;
+    uint64_t converted;
+    /* Largest safely castable integer expressible as double below 2^64. */
+    const double max_safe_uint64_real = 18446744073709547520.0;
+    if (!tg3__json_is_number(v) || !out) return 0;
+    if (v->type == TG3JSON_INT) {
+        if (v->u.integer < 0) return 0;
+        *out = (uint64_t)v->u.integer;
+        return 1;
+    }
+    real = v->u.real;
+    if (!isfinite(real) || real < 0.0 || real > max_safe_uint64_real) {
+        return 0;
+    }
+    converted = (uint64_t)real;
+    if ((double)converted != real) return 0;
+    *out = converted;
+    return 1;
+}
+
 static int tg3__json_is_object(const tg3json_value *v) { return v && v->type == TG3JSON_OBJECT; }
 static int tg3__json_is_array(const tg3json_value *v) { return v && v->type == TG3JSON_ARRAY; }
 
@@ -487,7 +527,6 @@ static int tg3__parse_string(tg3__parse_ctx *ctx, const tg3json_value *o, const
 static int tg3__parse_int(tg3__parse_ctx *ctx, const tg3json_value *o, const char *key,
                           int32_t *out, int required, const char *parent) {
     const tg3json_value *it = tg3__json_get(o, key);
-    int64_t v;
     if (!it) {
         if (required) {
             tg3__error_pushf(ctx->errors, ctx->arena, TG3_SEVERITY_ERROR, TG3_ERR_JSON_MISSING_FIELD,
@@ -501,13 +540,11 @@ static int tg3__parse_int(tg3__parse_ctx *ctx, const tg3json_value *o, const cha
                          parent, "Field '%s' must be a number", key);
         return 0;
     }
-    v = (it->type == TG3JSON_INT) ? it->u.integer : (int64_t)it->u.real;
-    if (v < INT32_MIN || v > INT32_MAX) {
+    if (!tg3__json_number_to_int32(it, out)) {
         tg3__error_pushf(ctx->errors, ctx->arena, TG3_SEVERITY_ERROR, TG3_ERR_JSON_TYPE_MISMATCH,
-                         parent, "Field '%s' value %" PRId64 " is out of range for int32", key, v);
+                         parent, "Field '%s' must be a finite int32-valued number", key);
         return 0;
     }
-    *out = (int32_t)v;
     return 1;
 }
 
@@ -527,8 +564,11 @@ static int tg3__parse_uint64(tg3__parse_ctx *ctx, const tg3json_value *o, const
                          parent, "Field '%s' must be a number", key);
         return 0;
     }
-    if (it->type == TG3JSON_INT) *out = it->u.integer >= 0 ? (uint64_t)it->u.integer : 0u;
-    else *out = it->u.real >= 0.0 ? (uint64_t)it->u.real : 0u;
+    if (!tg3__json_number_to_uint64(it, out)) {
+        tg3__error_pushf(ctx->errors, ctx->arena, TG3_SEVERITY_ERROR, TG3_ERR_JSON_TYPE_MISMATCH,
+                         parent, "Field '%s' must be a finite uint64-valued number", key);
+        return 0;
+    }
     return 1;
 }
 
@@ -651,7 +691,13 @@ static int tg3__parse_int_array(tg3__parse_ctx *ctx, const tg3json_value *o, con
     }
     for (i = 0; i < count; ++i) {
         const tg3json_value *item = tg3json_array_get(it, i);
-        arr[i] = item ? (int32_t)((item->type == TG3JSON_REAL) ? item->u.real : item->u.integer) : 0;
+        if (!item || !tg3__json_number_to_int32(item, &arr[i])) {
+            tg3__error_pushf(ctx->errors, ctx->arena, TG3_SEVERITY_ERROR,
+                             TG3_ERR_JSON_TYPE_MISMATCH, parent,
+                             "Field '%s' element %u must be a finite int32-valued number",
+                             key, (unsigned)i);
+            return 0;
+        }
     }
     *out = arr;
     *out_count = (uint32_t)count;
@@ -1155,7 +1201,13 @@ static int tg3__parse_primitive(tg3__parse_ctx *ctx, const tg3json_value *o, tg3
                 for (i = 0; i < count; ++i) {
                     const tg3json_object_entry *entry = tg3json_object_at(attr_it, i);
                     attrs[i].key = tg3__arena_str(ctx->arena, entry->key, (uint32_t)entry->key_len);
-                    attrs[i].value = (int32_t)((entry->value->type == TG3JSON_REAL) ? entry->value->u.real : entry->value->u.integer);
+                    if (!tg3__json_number_to_int32(entry->value, &attrs[i].value)) {
+                        tg3__error_pushf(ctx->errors, ctx->arena, TG3_SEVERITY_ERROR,
+                                         TG3_ERR_JSON_TYPE_MISMATCH, "/primitive/attributes",
+                                         "Attribute '%s' must be a finite int32-valued number",
+                                         entry->key ? entry->key : "");
+                        attrs[i].value = 0;
+                    }
                 }
                 prim->attributes = attrs;
                 prim->attributes_count = (uint32_t)count;
@@ -1186,7 +1238,13 @@ static int tg3__parse_primitive(tg3__parse_ctx *ctx, const tg3json_value *o, tg3
                         for (ai = 0; ai < acount; ++ai) {
                             const tg3json_object_entry *entry = tg3json_object_at(target_obj, ai);
                             tattrs[ai].key = tg3__arena_str(ctx->arena, entry->key, (uint32_t)entry->key_len);
-                            tattrs[ai].value = (int32_t)((entry->value->type == TG3JSON_REAL) ? entry->value->u.real : entry->value->u.integer);
+                            if (!tg3__json_number_to_int32(entry->value, &tattrs[ai].value)) {
+                                tg3__error_pushf(ctx->errors, ctx->arena, TG3_SEVERITY_ERROR,
+                                                 TG3_ERR_JSON_TYPE_MISMATCH, "/primitive/targets",
+                                                 "Target attribute '%s' must be a finite int32-valued number",
+                                                 entry->key ? entry->key : "");
+                                tattrs[ai].value = 0;
+                            }
                         }
                     }
                     target_arrays[ti] = tattrs;
@@ -1611,6 +1669,7 @@ TINYGLTF3_API tg3_error_code tg3_parse(tg3_model *model, tg3_error_stack *errors
     tg3json_value json_doc;
     const char *error_pos = NULL;
     tg3_error_code ret;
+    int parsed_ok;
     if (!options) { tg3_parse_options_init(&default_opts); options = &default_opts; }
     tg3__model_init(model);
     arena = tg3__arena_create(&options->memory);
@@ -1619,9 +1678,12 @@ TINYGLTF3_API tg3_error_code tg3_parse(tg3_model *model, tg3_error_stack *errors
         return TG3_ERR_OUT_OF_MEMORY;
     }
     model->arena_ = arena;
-    if (!tg3json_parse_n((const char *)json_data, (size_t)json_size, TINYGLTF3_MAX_NESTING_DEPTH, &json_doc, &error_pos) || json_doc.type != TG3JSON_OBJECT) {
+    parsed_ok = tg3json_parse_n((const char *)json_data, (size_t)json_size,
+                                TINYGLTF3_MAX_NESTING_DEPTH, &json_doc, &error_pos);
+    if (!parsed_ok || json_doc.type != TG3JSON_OBJECT) {
         tg3__error_push(errors, TG3_SEVERITY_ERROR, TG3_ERR_JSON_PARSE, "Failed to parse JSON", NULL,
                         error_pos ? (int64_t)(error_pos - (const char *)json_data) : -1);
+        if (parsed_ok) tg3json_value_free(&json_doc);
         if (model->arena_) { tg3__arena_destroy(model->arena_); model->arena_ = NULL; }
         return TG3_ERR_JSON_PARSE;
     }
@@ -1657,6 +1719,7 @@ TINYGLTF3_API tg3_error_code tg3_parse_glb(tg3_model *model, tg3_error_stack *er
     tg3json_value json_doc;
     const char *error_pos = NULL;
     tg3_error_code err;
+    int parsed_ok;
     err = tg3__parse_glb_header(glb_data, glb_size, &json_chunk, &json_chunk_size, &bin_chunk, &bin_chunk_size, errors);
     if (err != TG3_OK) return err;
     if (!options) { tg3_parse_options_init(&default_opts); options = &default_opts; }
@@ -1667,9 +1730,12 @@ TINYGLTF3_API tg3_error_code tg3_parse_glb(tg3_model *model, tg3_error_stack *er
         return TG3_ERR_OUT_OF_MEMORY;
     }
     model->arena_ = arena;
-    if (!tg3json_parse_n((const char *)json_chunk, (size_t)json_chunk_size, TINYGLTF3_MAX_NESTING_DEPTH, &json_doc, &error_pos) || json_doc.type != TG3JSON_OBJECT) {
+    parsed_ok = tg3json_parse_n((const char *)json_chunk, (size_t)json_chunk_size,
+                                TINYGLTF3_MAX_NESTING_DEPTH, &json_doc, &error_pos);
+    if (!parsed_ok || json_doc.type != TG3JSON_OBJECT) {
         tg3__error_push(errors, TG3_SEVERITY_ERROR, TG3_ERR_JSON_PARSE, "Failed to parse GLB JSON chunk", NULL,
                         error_pos ? (int64_t)(error_pos - (const char *)json_chunk) : -1);
+        if (parsed_ok) tg3json_value_free(&json_doc);
         tg3__arena_destroy(model->arena_);
         model->arena_ = NULL;
         return TG3_ERR_JSON_PARSE;
@@ -1717,6 +1783,7 @@ TINYGLTF3_API tg3_error_code tg3_parse_file(tg3_model *model, tg3_error_stack *e
     uint32_t i;
     if (options) opts = *options;
     else tg3_parse_options_init(&opts);
+    tg3__model_init(model);
 #ifdef TINYGLTF3_ENABLE_FS
     tg3__set_default_fs(&opts.fs);
 #endif