Fix TOB-EXECUTORCH-39, -42: validate tensor dimensions in XNNPACK compiler

Validate that dims array is non-null and num_dims matches the actual array
size in defineTensor to prevent heap buffer overflows. Change
flatbufferDimsToVector to return Result<> with null-check and per-dimension
validation against a 16M limit to prevent unbounded memory allocation from
malicious dimension values.

Authored-with: Claude

Author: Github Executorch

backends/xnnpack/runtime/XNNCompiler.cpp

@@ -285,9 +285,16 @@ Error defineTensor(
   }
 
   ET_CHECK_OR_RETURN_ERROR(
-      tensor_value != nullptr,
-      Internal,
-      "Deserialized Tensor is Null, this should never happen");
+      tensor_value != nullptr && tensor_value->dims() != nullptr,
+      InvalidProgram,
+      "Deserialized tensor is null, or tensor dims is null");
+
+  ET_CHECK_OR_RETURN_ERROR(
+      tensor_value->num_dims() == tensor_value->dims()->size(),
+      InvalidProgram,
+      "Tensor num_dims %u does not match dims array size %u",
+      tensor_value->num_dims(),
+      tensor_value->dims()->size());
 
   // Get tensor dims, here we need to use a vector in order
   // to properly convert the uint32_t* to size_t*
@@ -966,6 +973,10 @@ Error defineStaticTransposeNode(
   auto graph_node = node->xnode_union_as_XNNStaticTranspose();
 
   // Get tensor dims, we need to convert the uint32_t* to size_t*
+  ET_CHECK_OR_RETURN_ERROR(
+      graph_node->perm() != nullptr,
+      InvalidProgram,
+      "StaticTranspose: perm is null");
   std::vector<size_t> dims_data = flatbufferDimsToVector(graph_node->perm());
   xnn_status status = xnn_define_static_transpose(
       subgraph_ptr,
@@ -1031,6 +1042,11 @@ Error defineStaticConstantPadNode(
   const fb_xnnpack::XNNStaticConstantPad* graph_node =
       node->xnode_union_as_XNNStaticConstantPad();
 
+  ET_CHECK_OR_RETURN_ERROR(
+      graph_node->pre_paddings() != nullptr &&
+          graph_node->post_paddings() != nullptr,
+      InvalidProgram,
+      "StaticConstantPad: pre_paddings or post_paddings is null");
   std::vector<size_t> pre_paddings_dims =
       flatbufferDimsToVector(graph_node->pre_paddings());
   std::vector<size_t> post_paddings_dims =
@@ -1111,6 +1127,10 @@ Error defineStaticReshapeNode(
   auto graph_node = node->xnode_union_as_XNNStaticReshape();
 
   // Get tensor dims, we need to convert the uint32_t* to size_t*
+  ET_CHECK_OR_RETURN_ERROR(
+      graph_node->new_shape() != nullptr,
+      InvalidProgram,
+      "StaticReshape: new_shape is null");
   std::vector<size_t> dims_data =
       flatbufferDimsToVector(graph_node->new_shape());
   xnn_status status = xnn_define_static_reshape(
@@ -1406,6 +1426,10 @@ Error defineStaticSliceNode(
 
   auto graph_node = node->xnode_union_as_XNNStaticSlice();
 
+  ET_CHECK_OR_RETURN_ERROR(
+      graph_node->offsets() != nullptr && graph_node->sizes() != nullptr,
+      InvalidProgram,
+      "StaticSlice: offsets or sizes is null");
   std::vector<size_t> offsets = flatbufferDimsToVector(graph_node->offsets());
   std::vector<size_t> sizes = flatbufferDimsToVector(graph_node->sizes());