From b056a47fa0ab9bd818a9994b961d45d140fa54c7 Mon Sep 17 00:00:00 2001
From: Nicholas Cameron <ncameron@mozilla.com>
Date: Fri, 20 Apr 2012 21:07:55 +1200
Subject: [PATCH] Bug 733892; block reverting to the null last chance
 expception handler. r=ehsan

---
 .../windows/handler/exception_handler.h       |  8 ++--
 toolkit/crashreporter/nsExceptionHandler.cpp  | 43 +++++++++++++++++++
 2 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/toolkit/crashreporter/google-breakpad/src/client/windows/handler/exception_handler.h b/toolkit/crashreporter/google-breakpad/src/client/windows/handler/exception_handler.h
index 70d8ae17681..aa1eaf6f8e9 100644
--- a/toolkit/crashreporter/google-breakpad/src/client/windows/handler/exception_handler.h
+++ b/toolkit/crashreporter/google-breakpad/src/client/windows/handler/exception_handler.h
@@ -238,6 +238,10 @@ class ExceptionHandler {
   void RegisterAppMemory(void *ptr, size_t length);
   void UnregisterAppMemory(void *ptr);
 
+  // Called on the exception thread when an unhandled exception occurs.
+  // Signals the exception handler thread to handle the exception.
+  static LONG WINAPI HandleException(EXCEPTION_POINTERS* exinfo);
+
  private:
   friend class AutoExceptionHandler;
 
@@ -268,10 +272,6 @@ class ExceptionHandler {
   // Runs the main loop for the exception handler thread.
   static DWORD WINAPI ExceptionHandlerThreadMain(void* lpParameter);
 
-  // Called on the exception thread when an unhandled exception occurs.
-  // Signals the exception handler thread to handle the exception.
-  static LONG WINAPI HandleException(EXCEPTION_POINTERS* exinfo);
-
 #if _MSC_VER >= 1400  // MSVC 2005/8
   // This function will be called by some CRT functions when they detect
   // that they were passed an invalid parameter.  Note that in _DEBUG builds,
diff --git a/toolkit/crashreporter/nsExceptionHandler.cpp b/toolkit/crashreporter/nsExceptionHandler.cpp
index 770c4d3189d..09a8a2c1dd3 100644
--- a/toolkit/crashreporter/nsExceptionHandler.cpp
+++ b/toolkit/crashreporter/nsExceptionHandler.cpp
@@ -57,6 +57,8 @@
 #include "client/windows/handler/exception_handler.h"
 #include <DbgHelp.h>
 #include <string.h>
+
+#include "nsWindowsDllInterceptor.h"
 #elif defined(XP_MACOSX)
 #include "client/mac/crash_generation/client_info.h"
 #include "client/mac/crash_generation/crash_generation_server.h"
@@ -264,6 +266,31 @@ static const char* kSubprocessBlacklist[] = {
 class DelayedNote;
 nsTArray<nsAutoPtr<DelayedNote> >* gDelayedAnnotations;
 
+#if defined(XP_WIN)
+// the following are used to prevent other DLLs reverting the last chance
+// exception handler to the windows default. Any attempt to change the 
+// unhandled exception filter or to reset it is ignored and our crash
+// reporter is loaded instead (in case it became unloaded somehow)
+typedef LPTOP_LEVEL_EXCEPTION_FILTER (WINAPI *SetUnhandledExceptionFilter_func)
+  (LPTOP_LEVEL_EXCEPTION_FILTER lpTopLevelExceptionFilter);
+static SetUnhandledExceptionFilter_func stub_SetUnhandledExceptionFilter = 0;
+static WindowsDllInterceptor gKernel32Intercept;
+static bool gBlockUnhandledExceptionFilter = true;
+
+static LPTOP_LEVEL_EXCEPTION_FILTER WINAPI
+patched_SetUnhandledExceptionFilter (LPTOP_LEVEL_EXCEPTION_FILTER lpTopLevelExceptionFilter)
+{
+  if (!gBlockUnhandledExceptionFilter ||
+      lpTopLevelExceptionFilter == google_breakpad::ExceptionHandler::HandleException) {
+    // don't intercept
+    return stub_SetUnhandledExceptionFilter(lpTopLevelExceptionFilter);
+  }
+
+  // intercept attempts to change the filter
+  return NULL;
+}
+#endif
+
 #ifdef XP_MACOSX
 static cpu_type_t pref_cpu_types[2] = {
 #if defined(__i386__)
@@ -822,6 +849,17 @@ nsresult SetExceptionHandler(nsILocalFile* aXREDirectory,
 
 #ifdef XP_WIN
   gExceptionHandler->set_handle_debug_exceptions(true);
+  
+  // protect the crash reporter from being unloaded
+  gKernel32Intercept.Init("kernel32.dll");
+  bool ok = gKernel32Intercept.AddHook("SetUnhandledExceptionFilter",
+          reinterpret_cast<intptr_t>(patched_SetUnhandledExceptionFilter),
+          (void**) &stub_SetUnhandledExceptionFilter);
+
+#ifdef DEBUG
+  if (!ok)
+    printf_stderr ("SetUnhandledExceptionFilter hook failed; crash reporter is vulnerable.\n");
+#endif
 #endif
 
   // store application start time
@@ -1082,6 +1120,11 @@ static void OOPDeinit();
 
 nsresult UnsetExceptionHandler()
 {
+#ifdef XP_WIN
+  // allow SetUnhandledExceptionFilter
+  gBlockUnhandledExceptionFilter = false;
+#endif
+
   delete gExceptionHandler;
 
   // do this here in the unlikely case that we succeeded in allocating