Crash in `tf.strings.substr` due to `CHECK`-fail

Impact An attacker can cause a denial of service via CHECK-fail in tf.strings.substr with invalid arguments: python import tensorflow as tf tf.strings.substrinput='abc', len=1, pos=1,-1 python import tensorflow as tf tf.strings.substrinput='abc', len=1, pos=1,2 Patches We have received a patch fo...