From 9bc90adc09727c65efeb2b4c547542bf9576744e Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <nnethercote@mozilla.com>
Date: Fri, 9 Aug 2019 00:58:55 +0000
Subject: [PATCH] Bug 1570212 - Make security.turn_off_all_security... a
 non-VarCache pref. r=mccr8

This could be made into a static pref, but then it would be always defined and
thus visible in about:config, which seems undesirable for such a senstive pre.
So this patch uses a callback that makes it work just like the existing
VarCache, i.e. it's not defined by default, in which case it defaults to false.

Differential Revision: https://phabricator.services.mozilla.com/D40343

--HG--
extra : moz-landing-system : lando
---
 js/xpconnect/src/nsXPConnect.cpp | 18 ++++++++++++++++++
 js/xpconnect/src/xpcpublic.h     | 10 ++++------
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/js/xpconnect/src/nsXPConnect.cpp b/js/xpconnect/src/nsXPConnect.cpp
index 794d2066a171..2eec7e719432 100644
--- a/js/xpconnect/src/nsXPConnect.cpp
+++ b/js/xpconnect/src/nsXPConnect.cpp
@@ -1210,3 +1210,21 @@ void xpc::YieldCooperativeContext() {
 void xpc::ResumeCooperativeContext() {
   JS_ResumeCooperativeContext(XPCJSContext::Get()->Context());
 }
+
+void xpc::CacheAutomationPref(bool* aMirror) {
+  // The obvious thing is to make this pref a static pref. But then it would
+  // always be defined and always show up in about:config, and users could flip
+  // it, which we don't want. Instead we roll our own callback so that if the
+  // pref is undefined (the normal case) then sAutomationPrefIsSet is false and
+  // nothing shows up in about:config.
+  nsresult rv = mozilla::Preferences::RegisterCallbackAndCall(
+      [](const char* aPrefName, void* aData) {
+        auto aMirror = static_cast<bool*>(aData);
+        *aMirror =
+            mozilla::Preferences::GetBool(aPrefName, /* aFallback */ false);
+      },
+      "security."
+      "turn_off_all_security_so_that_viruses_can_take_over_this_computer",
+      static_cast<void*>(aMirror));
+  MOZ_RELEASE_ASSERT(NS_SUCCEEDED(rv));
+}
diff --git a/js/xpconnect/src/xpcpublic.h b/js/xpconnect/src/xpcpublic.h
index 4d3532f9b033..69632a7460e2 100644
--- a/js/xpconnect/src/xpcpublic.h
+++ b/js/xpconnect/src/xpcpublic.h
@@ -679,15 +679,13 @@ inline bool AreNonLocalConnectionsDisabled() {
   return disabledForTest;
 }
 
+void CacheAutomationPref(bool* aPref);
+
 inline bool IsInAutomation() {
-  static bool sAutomationPrefIsSet;
+  static bool sAutomationPrefIsSet = false;
   static bool sPrefCacheAdded = false;
   if (!sPrefCacheAdded) {
-    mozilla::Preferences::AddBoolVarCache(
-        &sAutomationPrefIsSet,
-        "security.turn_off_all_security_so_that_viruses_can_take_over_this_"
-        "computer",
-        false);
+    CacheAutomationPref(&sAutomationPrefIsSet);
     sPrefCacheAdded = true;
   }
   return sAutomationPrefIsSet && AreNonLocalConnectionsDisabled();