Expose enable/disable switch for shill sandboxing over DBus

This feature flag gates the use of minijail to sandbox shill (the
network manager) on CrOS. Defaults to true. We want a feature flag for
this in case any unforseen sandboxing compications occur on the beta or
stable channels and Finch is our only way of reverting.

CQ-DEPEND=CL:1172729,CL:1177883
"sudo -u chronos dbus-send --system --type=method_call --print-reply \
--dest=org.chromium.ChromeFeaturesService \
/org/chromium/ChromeFeaturesService \
"org.chromium.ChromeFeaturesServiceInterface.IsShillSandboxingEnabled"

Bug: 649417
Test: Following command returned true (flag is true by default):
Change-Id: I359b28d463f8f0ce861739d7f165f5437690bae5
Reviewed-on: https://chromium-review.googlesource.com/1173260
Commit-Queue: Micah Morton <mortonm@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583750}

chrome/browser/chromeos/dbus/finch_features_service_provider_delegate.cc

@@ -34,4 +34,8 @@ bool FinchFeaturesServiceProviderDelegate::IsUsbguardEnabled() {
   return base::FeatureList::IsEnabled(features::kUsbguard);
 }
 
+bool FinchFeaturesServiceProviderDelegate::IsShillSandboxingEnabled() {
+  return base::FeatureList::IsEnabled(features::kShillSandboxing);
+}
+
 }  // namespace chromeos

chrome/browser/chromeos/dbus/finch_features_service_provider_delegate.h

@@ -20,6 +20,7 @@ class FinchFeaturesServiceProviderDelegate
   // ChromeServiceProvider::Delegate:
   bool IsCrostiniEnabled(const std::string& user_id_hash) override;
   bool IsUsbguardEnabled() override;
+  bool IsShillSandboxingEnabled() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FinchFeaturesServiceProviderDelegate);

chrome/common/chrome_features.cc

@@ -656,6 +656,10 @@ const base::Feature kMachineLearningService{"MachineLearningService",
 // Enable USBGuard at the lockscreen on Chrome OS.
 // TODO(crbug.com/874630): Remove this kill-switch
 const base::Feature kUsbguard{"USBGuard", base::FEATURE_ENABLED_BY_DEFAULT};
+
+// Enable running shill in a minijail sandbox on Chrome OS.
+const base::Feature kShillSandboxing{"ShillSandboxing",
+                                     base::FEATURE_DISABLED_BY_DEFAULT};
 #endif  // defined(OS_CHROMEOS)
 
 #if !defined(OS_ANDROID)

chrome/common/chrome_features.h

@@ -353,6 +353,8 @@ extern const base::Feature kCrOSEnableUSMUserService;
 extern const base::Feature kMachineLearningService;
 
 extern const base::Feature kUsbguard;
+
+extern const base::Feature kShillSandboxing;
 #endif  // defined(OS_CHROMEOS)
 
 #if !defined(OS_ANDROID)

chromeos/dbus/services/chrome_features_service_provider.cc

@@ -35,6 +35,14 @@ void ChromeFeaturesServiceProvider::Start(
                           weak_ptr_factory_.GetWeakPtr()),
       base::BindRepeating(&ChromeFeaturesServiceProvider::OnExported,
                           weak_ptr_factory_.GetWeakPtr()));
+  exported_object->ExportMethod(
+      kChromeFeaturesServiceInterface,
+      kChromeFeaturesServiceIsShillSandboxingEnabledMethod,
+      base::BindRepeating(
+          &ChromeFeaturesServiceProvider::IsShillSandboxingEnabled,
+          weak_ptr_factory_.GetWeakPtr()),
+      base::BindRepeating(&ChromeFeaturesServiceProvider::OnExported,
+                          weak_ptr_factory_.GetWeakPtr()));
 }
 
 void ChromeFeaturesServiceProvider::OnExported(
@@ -76,4 +84,14 @@ void ChromeFeaturesServiceProvider::IsUsbguardEnabled(
   response_sender.Run(std::move(response));
 }
 
+void ChromeFeaturesServiceProvider::IsShillSandboxingEnabled(
+    dbus::MethodCall* method_call,
+    dbus::ExportedObject::ResponseSender response_sender) {
+  std::unique_ptr<dbus::Response> response =
+      dbus::Response::FromMethodCall(method_call);
+  dbus::MessageWriter writer(response.get());
+  writer.AppendBool(delegate_->IsShillSandboxingEnabled());
+  response_sender.Run(std::move(response));
+}
+
 }  // namespace chromeos

chromeos/dbus/services/chrome_features_service_provider.h

@@ -42,6 +42,7 @@ class CHROMEOS_EXPORT ChromeFeaturesServiceProvider
 
     virtual bool IsCrostiniEnabled(const std::string& user_id_hash) = 0;
     virtual bool IsUsbguardEnabled() = 0;
+    virtual bool IsShillSandboxingEnabled() = 0;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(Delegate);
@@ -65,6 +66,9 @@ class CHROMEOS_EXPORT ChromeFeaturesServiceProvider
                          dbus::ExportedObject::ResponseSender response_sender);
   void IsUsbguardEnabled(dbus::MethodCall* method_call,
                          dbus::ExportedObject::ResponseSender response_sender);
+  void IsShillSandboxingEnabled(
+      dbus::MethodCall* method_call,
+      dbus::ExportedObject::ResponseSender response_sender);
 
   std::unique_ptr<Delegate> delegate_;
   // Keep this last so that all weak pointers will be invalidated at the