Arbitrary memory read in `ImmutableConst`
ImpactThe `ImmutableConst` operation in TensorFlow can be tricked into reading arbitrary memory contents:This is because the `tstring` TensorFlow string class has a special case for memory mapped strings but the operation itself does not offer any support for this datatype.PatchesWe have patched the issue in GitHub commit [3712a2d3455e6ccb924daa5724a3652a86f6b585](https://github.com/tensorflow/tensorflow/commit/3712a2d3455e6ccb924daa5724a3652a86f6b585) and GitHub commit [1cb6bb6c2a6019417c9adaf9e6843ba75ee2580b](https://github.com/tensorflow/tensorflow/commit/1cb6bb6c2a6019417c9adaf9e6843ba75ee2580b).The fix will be included in TensorFlow 2.7.0. We will also cherrypick this commit on TensorFlow 2.6.1, TensorFlow 2.5.2, and TensorFlow 2.4.4, as these are also affected and still in supported range.For more informationPlease consult [our security guide](https://github.com/tensorflow/tensorflow/blob/master/SECURITY.md) for more information regarding the security model and how to contact us with issues and questions.AttributionThis vulnerability has been reported by members of the Aivul Team from Qihoo 360.