[StatsPlugin] Fix use-after-free issue (#36664)

Fix https://github.com/grpc/grpc/issues/36663

Closes #36664

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36664 from yashykt:StatsPluginFixUseAfterFree 107c341349
PiperOrigin-RevId: 635555326

src/core/lib/surface/legacy_channel.cc

@@ -93,13 +93,13 @@ absl::StatusOr<OrphanablePtr<Channel>> LegacyChannel::Create(
     *(*r)->stats_plugin_group =
         GlobalStatsPluginRegistry::GetStatsPluginsForServer(args);
   } else {
-    experimental::StatsPluginChannelScope scope(
-        target, args.GetOwnedString(GRPC_ARG_DEFAULT_AUTHORITY)
-                    .value_or(CoreConfiguration::Get()
-                                  .resolver_registry()
-                                  .GetDefaultAuthority(target)));
+    std::string authority = args.GetOwnedString(GRPC_ARG_DEFAULT_AUTHORITY)
+                                .value_or(CoreConfiguration::Get()
+                                              .resolver_registry()
+                                              .GetDefaultAuthority(target));
     *(*r)->stats_plugin_group =
-        GlobalStatsPluginRegistry::GetStatsPluginsForChannel(scope);
+        GlobalStatsPluginRegistry::GetStatsPluginsForChannel(
+            experimental::StatsPluginChannelScope(target, authority));
   }
   return MakeOrphanable<LegacyChannel>(
       grpc_channel_stack_type_is_client(builder.channel_stack_type()),

test/cpp/ext/otel/otel_plugin_test.cc

@@ -471,6 +471,28 @@ TEST_F(OpenTelemetryPluginEnd2EndTest, NoMeterProviderRegistered) {
   SendRPC();
 }
 
+// Test that the otel plugin sees the expected channel target and default
+// authority.
+TEST_F(OpenTelemetryPluginEnd2EndTest, VerifyChannelScopeTargetAndAuthority) {
+  Init(std::move(
+      Options()
+          .set_metric_names({grpc::OpenTelemetryPluginBuilder::
+                                 kClientAttemptStartedInstrumentName})
+          .set_channel_scope_filter(
+              [&](const OpenTelemetryPluginBuilder::ChannelScope& scope) {
+                return scope.target() == canonical_server_address_ &&
+                       scope.default_authority() == server_address_;
+              })));
+  SendRPC();
+  const char* kMetricName = "grpc.client.attempt.started";
+  auto data = ReadCurrentMetricsData(
+      [&](const absl::flat_hash_map<
+          std::string,
+          std::vector<opentelemetry::sdk::metrics::PointDataAttributes>>&
+              data) { return !data.contains(kMetricName); });
+  ASSERT_EQ(data[kMetricName].size(), 1);
+}
+
 // Test that a channel scope filter returning true records metrics on the
 // channel.
 TEST_F(OpenTelemetryPluginEnd2EndTest, ChannelScopeFilterReturnsTrue) {