From 117457a76780e49b599b393b471feee894ced4a8 Mon Sep 17 00:00:00 2001
From: "Mark D. Roth" <roth@google.com>
Date: Fri, 3 Feb 2023 15:32:55 -0800
Subject: [PATCH] xDS: reject aggregate cluster with empty cluster list
 (#32238)

---
 src/core/ext/xds/xds_cluster.cc               |  4 ++++
 .../xds/xds_cluster_resource_type_test.cc     | 23 +++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/src/core/ext/xds/xds_cluster.cc b/src/core/ext/xds/xds_cluster.cc
index d5f0d0dde58..e2f5e727f65 100644
--- a/src/core/ext/xds/xds_cluster.cc
+++ b/src/core/ext/xds/xds_cluster.cc
@@ -306,6 +306,10 @@ XdsClusterResource::Aggregate AggregateClusterParse(
   const upb_StringView* clusters =
       envoy_extensions_clusters_aggregate_v3_ClusterConfig_clusters(
           aggregate_cluster_config, &size);
+  if (size == 0) {
+    ValidationErrors::ScopedField field(errors, ".clusters");
+    errors->AddError("must be non-empty");
+  }
   for (size_t i = 0; i < size; ++i) {
     aggregate.prioritized_cluster_names.emplace_back(
         UpbStringToStdString(clusters[i]));
diff --git a/test/core/xds/xds_cluster_resource_type_test.cc b/test/core/xds/xds_cluster_resource_type_test.cc
index 4e6ff7273cb..8be5b86873d 100644
--- a/test/core/xds/xds_cluster_resource_type_test.cc
+++ b/test/core/xds/xds_cluster_resource_type_test.cc
@@ -581,6 +581,29 @@ TEST_F(ClusterTypeTest, AggregateClusterUnparseableProto) {
       << decode_result.resource.status();
 }
 
+TEST_F(ClusterTypeTest, AggregateClusterEmptyClusterList) {
+  Cluster cluster;
+  cluster.set_name("foo");
+  cluster.mutable_cluster_type()->set_name("envoy.clusters.aggregate");
+  cluster.mutable_cluster_type()->mutable_typed_config()->PackFrom(
+      ClusterConfig());
+  std::string serialized_resource;
+  ASSERT_TRUE(cluster.SerializeToString(&serialized_resource));
+  auto* resource_type = XdsClusterResourceType::Get();
+  auto decode_result =
+      resource_type->Decode(decode_context_, serialized_resource);
+  ASSERT_TRUE(decode_result.name.has_value());
+  EXPECT_EQ(*decode_result.name, "foo");
+  EXPECT_EQ(decode_result.resource.status().code(),
+            absl::StatusCode::kInvalidArgument);
+  EXPECT_EQ(decode_result.resource.status().message(),
+            "errors validating Cluster resource: ["
+            "field:cluster_type.typed_config.value["
+            "envoy.extensions.clusters.aggregate.v3.ClusterConfig].clusters "
+            "error:must be non-empty]")
+      << decode_result.resource.status();
+}
+
 //
 // LB policy tests
 //