[jit] Validate mobile module fields parsed by flatbuffer loader (pyto…

…rch#127437)

Fixing error in `torch.jit.load` Python API function that cause crash in C-backend of PyTorch.
The mobile module is succesfully parsed from flatbuffer format, but its fields are used without any validation.

Fixes pytorch#127434

Pull Request resolved: pytorch#127437
Approved by: https://github.com/davidberard98

torch/csrc/jit/mobile/flatbuffer_loader.cpp

@@ -296,6 +296,11 @@ mobile::Module FlatbufferLoader::parseModule(
       "Parsing flatbuffer module: Corrupted ivalues/object_types field");
   TORCH_CHECK(
       reinterpret_cast<const char*>(ivalues) < end, "Corrupted ivalues field");
+  TORCH_CHECK(
+      module->storage_data_size() >= 0,
+      "Parsing flatbuffer module: illegal storage_data_size: ",
+      module->storage_data_size(),
+      ", expected to be non negative");
   all_ivalues_.resize(ivalues->size());
   all_types_.resize(module->object_types()->size());
   storages_.resize(module->storage_data_size());