[wasm] Read global names only if their name length is valid.

BUG=chromium:642987
R=titzer@chromium.org
TEST=module-decoder-unittest.cc:GlobalWithInvalidNameLength

Review-Url: https://codereview.chromium.org/2301873002
Cr-Commit-Position: refs/heads/master@{#39071}

src/wasm/module-decoder.cc

@@ -461,7 +461,8 @@ class ModuleDecoder : public Decoder {
   // Decodes a single global entry inside a module starting at {pc_}.
   void DecodeGlobalInModule(WasmGlobal* global) {
     global->name_offset = consume_string(&global->name_length, false);
-    if (!unibrow::Utf8::Validate(start_ + global->name_offset,
+    if (ok() &&
+        !unibrow::Utf8::Validate(start_ + global->name_offset,
                                  global->name_length)) {
       error("global name is not valid utf8");
     }

test/unittests/wasm/module-decoder-unittest.cc

@@ -279,6 +279,18 @@ TEST_F(WasmModuleVerifyTest, GlobalWithInvalidNameOffset) {
   EXPECT_FAILURE(data);
 }
 
+TEST_F(WasmModuleVerifyTest, GlobalWithInvalidNameLength) {
+  static const byte data[] = {
+      SECTION(GLOBALS, 5),  // --
+      1,
+      NAME_LENGTH(56),  // invalid length
+      'g',              // name
+      kLocalI32,        // memory type
+      0,                // exported
+  };
+  EXPECT_FAILURE(data);
+}
+
 TEST_F(WasmModuleVerifyTest, GlobalWithInvalidMemoryType) {
   static const byte data[] = {
       SECTION(GLOBALS, 7),