Bug 1443925 - Part 5: Make it possible to get the system principal from any thread, r=ckerschb

This is required because the script security manager which currently owns the
singleton is main-thread only. This change still ties the lifecycle of the
static to that service, but also makes it generally available from any thread.

Differential Revision: https://phabricator.services.mozilla.com/D163035

caps/SystemPrincipal.cpp

@@ -7,6 +7,7 @@
 
 #include "nscore.h"
 #include "SystemPrincipal.h"
+#include "mozilla/ClearOnShutdown.h"
 #include "nsCOMPtr.h"
 #include "nsReadableUtils.h"
 #include "nsCRT.h"
@@ -29,9 +30,31 @@ SystemPrincipal::SystemPrincipal()
     : BasePrincipal(eSystemPrincipal, kSystemPrincipalSpec,
                     OriginAttributes()) {}
 
-already_AddRefed<SystemPrincipal> SystemPrincipal::Create() {
-  RefPtr<SystemPrincipal> sp = new SystemPrincipal();
-  return sp.forget();
+static StaticMutex sSystemPrincipalMutex;
+static StaticRefPtr<SystemPrincipal> sSystemPrincipal
+    MOZ_GUARDED_BY(sSystemPrincipalMutex);
+
+already_AddRefed<SystemPrincipal> SystemPrincipal::Get() {
+  StaticMutexAutoLock lock(sSystemPrincipalMutex);
+  return do_AddRef(sSystemPrincipal);
+}
+
+already_AddRefed<SystemPrincipal> SystemPrincipal::Init() {
+  AssertIsOnMainThread();
+  StaticMutexAutoLock lock(sSystemPrincipalMutex);
+  if (MOZ_UNLIKELY(sSystemPrincipal)) {
+    MOZ_ASSERT_UNREACHABLE("SystemPrincipal::Init() may only be called once");
+  } else {
+    sSystemPrincipal = new SystemPrincipal();
+  }
+  return do_AddRef(sSystemPrincipal);
+}
+
+void SystemPrincipal::Shutdown() {
+  AssertIsOnMainThread();
+  StaticMutexAutoLock lock(sSystemPrincipalMutex);
+  MOZ_ASSERT(sSystemPrincipal);
+  sSystemPrincipal = nullptr;
 }
 
 nsresult SystemPrincipal::GetScriptLocation(nsACString& aStr) {

caps/SystemPrincipal.h

@@ -22,6 +22,8 @@
   }
 #define NS_SYSTEMPRINCIPAL_CONTRACTID "@mozilla.org/systemprincipal;1"
 
+class nsScriptSecurityManager;
+
 namespace Json {
 class Value;
 }
@@ -32,7 +34,7 @@ class SystemPrincipal final : public BasePrincipal, public nsISerializable {
   SystemPrincipal();
 
  public:
-  static already_AddRefed<SystemPrincipal> Create();
+  static already_AddRefed<SystemPrincipal> Get();
 
   static PrincipalKind Kind() { return eSystemPrincipal; }
 
@@ -61,8 +63,13 @@ class SystemPrincipal final : public BasePrincipal, public nsISerializable {
   }
 
  protected:
+  friend class ::nsScriptSecurityManager;
+
   virtual ~SystemPrincipal() = default;
 
+  static already_AddRefed<SystemPrincipal> Init();
+  static void Shutdown();
+
   bool SubsumesInternal(nsIPrincipal* aOther,
                         DocumentDomainConsideration aConsideration) override {
     return true;

caps/nsScriptSecurityManager.cpp

@@ -1554,9 +1554,7 @@ nsresult nsScriptSecurityManager::Init() {
   InitPrefs();
 
   // Create our system principal singleton
-  RefPtr<SystemPrincipal> system = SystemPrincipal::Create();
-
-  mSystemPrincipal = system;
+  mSystemPrincipal = SystemPrincipal::Init();
 
   return NS_OK;
 }
@@ -1600,6 +1598,7 @@ nsScriptSecurityManager::~nsScriptSecurityManager(void) {
 void nsScriptSecurityManager::Shutdown() {
   NS_IF_RELEASE(sIOService);
   BundleHelper::Shutdown();
+  SystemPrincipal::Shutdown();
 }
 
 nsScriptSecurityManager* nsScriptSecurityManager::GetScriptSecurityManager() {

dom/ipc/PermissionMessageUtils.cpp

@@ -15,8 +15,6 @@ namespace mozilla::ipc {
 void IPDLParamTraits<nsIPrincipal*>::Write(IPC::MessageWriter* aWriter,
                                            IProtocol* aActor,
                                            nsIPrincipal* aParam) {
-  MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread());
-
   Maybe<PrincipalInfo> info;
   if (aParam) {
     info.emplace();