CVE-2022-23577: Null-dereference in Tensorflow

The implementation of GetInitOp is vulnerable to a crash caused by dereferencing a null pointer:

const auto& init_op_sig_it =
meta_graph_def.signature_def().find(kSavedModelInitOpSignatureKey);
if (init_op_sig_it != sig_def_map.end()) {
*init_op_name = init_op_sig_it->second.outputs()
.find(kSavedModelInitOpSignatureKey)
->second.name();
return Status::OK();
}

Here, we have a nested map and we assume that if the first .find succeeds then so would be the search in the internal map. However, the maps are built based on the SavedModel protobuf format and a malicious user can alter that on disk before loading to cause the second .find to return nullptr.