Fix iOS termination crash

jpsim · jpsim · commit 424ed0e8e634 · 2022-02-15T15:56:31.000-05:00
When iOS is terminating a process, it may release some static memory,
which could cause the `event_dispatcher_` variable to point to invalid
memory, leading to a crash.

A crash that occurs when an app is already in the process of being
terminated isn't too bad, considering it's already shutting down, but
this matters to some extent, considering that crash reporters will
report this as an app crash, and the OS may choose to penalize your app
by not proactively suggesting it.

This should fix a crash with a backtrace such as this one:

```
EXC_BAD_ACCESS: Attempted to dereference garbage pointer 0x8000000000000010.

0 Envoy::Event::ProvisionalDispatcher::post(std::__1::function&lt;void ()&gt;)
1 Envoy::EngineHandle::runOnEngineDispatcher(long, std::__1::function&lt;void (Envoy::Engine&amp;)&gt;)
2 start_stream
3 -[EnvoyHTTPStreamImpl initWithHandle:callbacks:explicitFlowControl:]
4 -[EnvoyEngineImpl startStreamWithCallbacks:explicitFlowControl:]
5 StreamPrototype.start(queue:)
```

Signed-off-by: JP Simard &lt;jp@jpsim.com&gt;
diff --git a/library/cc/engine.cc b/library/cc/engine.cc
@@ -26,5 +26,7 @@ void Engine::terminate() {
   terminated_ = true;
 }
 
+bool Engine::isTerminated() { return terminated_; }
+
 } // namespace Platform
 } // namespace Envoy
diff --git a/library/cc/engine.h b/library/cc/engine.h
@@ -19,6 +19,7 @@ class Engine : public std::enable_shared_from_this<Engine> {
   PulseClientSharedPtr pulseClient();
 
   void terminate();
+  bool isTerminated();
 
 private:
   Engine(envoy_engine_t engine);
diff --git a/library/common/engine.h b/library/common/engine.h
@@ -42,6 +42,11 @@ class Engine : public Logger::Loggable<Logger::Id::main> {
    */
   envoy_status_t terminate();
 
+  /**
+   * Whether this engine has been terminated.
+   */
+  bool isTerminated();
+
   /**
    * Accessor for the provisional event dispatcher.
    * @return Event::ProvisionalDispatcher&, the engine dispatcher.
diff --git a/library/common/engine_handle.cc b/library/common/engine_handle.cc
@@ -5,6 +5,10 @@ namespace Envoy {
 envoy_status_t EngineHandle::runOnEngineDispatcher(envoy_engine_t,
                                                    std::function<void(Envoy::Engine&)> func) {
   if (auto e = engine()) {
+    if (e->isTerminated()) {
+      return ENVOY_FAILURE;
+    }
+
     return e->dispatcher().post([func]() {
       if (auto e = engine()) {
         func(*e);

Original file line number	Diff line number	Diff line change
`@@ -26,5 +26,7 @@ void Engine::terminate() {`
`26`	`26`	`terminated_ = true;`
`27`	`27`	`}`
`28`	`28`
	`29`	`+bool Engine::isTerminated() { return terminated_; }`
	`30`	`+`
`29`	`31`	`} // namespace Platform`
`30`	`32`	`} // namespace Envoy`