Handle a special grappler case resulting in crash.

It might happen that a malformed input could be used to trick Grappler into trying to optimize a node with no inputs. This, in turn, would produce a null pointer dereference and a segfault.

PiperOrigin-RevId: 369242852
Change-Id: I2e5cbe7aec243d34a6d60220ac8ac9b16f136f6b

tensorflow/core/grappler/optimizers/arithmetic_optimizer.cc

@@ -2047,6 +2047,12 @@ class ReorderCastLikeAndValuePreserving : public ArithmeticOptimizerStage {
 
   Status TrySimplify(NodeDef* consumer, string* simplified_node_name) override {
     NodeDef* producer;
+
+    if (consumer->input_size() < 1) {
+      return errors::FailedPrecondition("Node ", simplified_node_name,
+                                        " lacks inputs");
+    }
+
     TF_RETURN_IF_ERROR(GetInputNode(consumer->input(0), &producer));
     const bool producer_is_cast = IsCastLike(*producer);
     const bool can_optimize =
@@ -2538,6 +2544,11 @@ class ReplaceMulWithSquare : public ArithmeticOptimizerStage {
   ~ReplaceMulWithSquare() override = default;
 
   bool IsSupported(const NodeDef* node) const override {
+    if (!node || node->input_size() < 2) {
+      // Invalid node
+      return false;
+    }
+
     return IsAnyMul(*node) && node->input(0) == node->input(1);
   }
 

tensorflow/core/grappler/optimizers/dependency_optimizer.cc

@@ -68,6 +68,12 @@ bool DependencyOptimizer::SafeToRemoveIdentity(const NodeDef& node) const {
     // The output values of this node may be needed.
     return false;
   }
+
+  if (node.input_size() < 1) {
+    // Node lacks input, is invalid
+    return false;
+  }
+
   const NodeDef* input = node_map_->GetNode(NodeName(node.input(0)));
   CHECK(input != nullptr) << "node = " << node.name()
                           << " input = " << node.input(0);