Bug 1522830: Part 2 - Make launcher blocklist work in child processes; r=mhowell

* We change `InitializeDllBlocklistOOP` to be able to set the correct flags
  when initializing a sandbox child process.
* We change the freestanding DLL blocklist code to be sensitive to the
  `CHILD_PROCESSES_ONLY` flag;
* We move the declaration of `gBlocklistInitFlags` to `WindowsDllBlocklist.h`
  so that it is visible to more code.

Differential Revision: https://phabricator.services.mozilla.com/D53674

--HG--
extra : moz-landing-system : lando

browser/app/winlauncher/DllBlocklistInit.cpp

@@ -17,8 +17,6 @@
 #include "DllBlocklistInit.h"
 #include "freestanding/DllBlocklist.h"
 
-extern uint32_t gBlocklistInitFlags;
-
 #if defined(_MSC_VER)
 extern "C" IMAGE_DOS_HEADER __ImageBase;
 #endif
@@ -101,6 +99,13 @@ LauncherVoidResult InitializeDllBlocklistOOP(const wchar_t* aFullImagePath,
 
   // Tell the mozglue blocklist that we have bootstrapped
   uint32_t newFlags = eDllBlocklistInitFlagWasBootstrapped;
+
+  if (gBlocklistInitFlags & eDllBlocklistInitFlagWasBootstrapped) {
+    // If we ourselves were bootstrapped, then we are starting a child process
+    // and need to set the appropriate flag.
+    newFlags |= eDllBlocklistInitFlagIsChildProcess;
+  }
+
   ok = !!::WriteProcessMemory(aChildProcess, &gBlocklistInitFlags, &newFlags,
                               sizeof(newFlags), &bytesWritten);
   if (!ok || bytesWritten != sizeof(newFlags)) {

browser/app/winlauncher/freestanding/DllBlocklist.cpp

@@ -9,6 +9,7 @@
 #include "mozilla/BinarySearch.h"
 #include "mozilla/NativeNt.h"
 #include "mozilla/Types.h"
+#include "mozilla/WindowsDllBlocklist.h"
 
 #include "DllBlocklist.h"
 #include "LoaderPrivateAPI.h"
@@ -180,9 +181,8 @@ static BlockAction CheckBlockInfo(const DllBlockInfo* aInfo, void* aBaseAddress,
     }
   }
 
-  // We're not bootstrapping child processes at this time, so this case is
-  // always true.
-  if (aInfo->mFlags & DllBlockInfo::CHILD_PROCESSES_ONLY) {
+  if ((aInfo->mFlags & DllBlockInfo::CHILD_PROCESSES_ONLY) &&
+      !(gBlocklistInitFlags & eDllBlocklistInitFlagIsChildProcess)) {
     return BlockAction::Allow;
   }
 

mozglue/dllservices/WindowsDllBlocklist.h

@@ -22,6 +22,11 @@ enum DllBlocklistInitFlags {
   eDllBlocklistInitFlagWasBootstrapped = 2
 };
 
+// Only available from within firefox.exe
+#  if !defined(IMPL_MFBT) && !defined(MOZILLA_INTERNAL_API)
+extern uint32_t gBlocklistInitFlags;
+#  endif  // !defined(IMPL_MFBT) && !defined(MOZILLA_INTERNAL_API)
+
 MFBT_API void DllBlocklist_Initialize(
     uint32_t aInitFlags = eDllBlocklistInitFlagDefault);
 MFBT_API void DllBlocklist_WriteNotes(CrashReporter::AnnotationWriter& aWriter);