OOB access in GLM SoftMax (#3642)

closes #3590

Authors:
  - Divye Gala (@divyegala)

Approvers:
  - William Hicks (@wphicks)
  - John Zedlewski (@JohnZed)

URL: #3642

cpp/src/glm/qn/glm_softmax.cuh

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, NVIDIA CORPORATION.
+ * Copyright (c) 2018-2021, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -59,7 +59,11 @@ __global__ void logSoftmaxKernel(T *out, T *dZ, const T *in, const T *labels,
   bool delta = false;
   // TODO is there a better way to read this?
   if (getDerivative && threadIdx.x == 0) {
-    shm.sh_val[threadIdx.y] = labels[y];
+    if (y < N) {
+      shm.sh_val[threadIdx.y] = labels[y];
+    } else {
+      shm.sh_val[threadIdx.y] = std::numeric_limits<T>::lowest();
+    }
   }
   __syncthreads();
   T label = shm.sh_val[threadIdx.y];