Fix abort() call on appsec helper unload

runner was living too long (until shared library unload) due to a static
shared pointer used for RC notifications. Plus, the destructor would
have a call to shared_for_this(), which would try to revive the shared
pointer being destroyed, which raise an exception due to there being no
shared pointer anymore. We would catch this and abort().

Instead, destroy the runner earlier (when its own thread finishes).
Reset the static shared pointer just before that.

Author: cataphract

appsec/src/helper/main.cpp

@@ -125,6 +125,8 @@ int appsec_helper_main_impl()
 
         runner->run();
 
+        runner->unregister_for_rc_notifications();
+
         finished.store(true, std::memory_order_release);
     }};
     thread_id = thr.native_handle();

appsec/src/helper/runner.cpp

@@ -123,7 +123,7 @@ void runner::register_for_rc_notifications()
                 std::atomic_load(&RUNNER_FOR_NOTIFICATIONS);
             if (!runner) {
                 // NOLINTNEXTLINE(bugprone-lambda-function-name)
-                SPDLOG_ERROR("No runner to notify of remote config updates");
+                SPDLOG_WARN("No runner to notify of remote config updates");
                 ddog_remote_config_path_free(path);
                 return;
             }
@@ -136,15 +136,19 @@ void runner::register_for_rc_notifications()
         });
 }
 
-runner::~runner() noexcept
+void runner::unregister_for_rc_notifications()
 {
+    SPDLOG_INFO("Unregister runner for RC update callback");
     try {
         std::shared_ptr<runner> expected = shared_from_this();
         std::atomic_compare_exchange_strong(&RUNNER_FOR_NOTIFICATIONS,
             &expected, std::shared_ptr<runner>(nullptr));
     } catch (...) {
-        // can only happened if there is no shared_ptr for the runner
-        // in this case a std::bad_weak_ptr is thrown
+        // can only happen if there is no shared_ptr for the runner
+        // in this case a std::bad_weak_ptr is thrown.
+        // But we only expose runner through a shared pointer, so this would
+        // require extraordinary actions to destroy the shared pointer but not
+        // the object.
         std::abort();
     }
 }

appsec/src/helper/runner.hpp

@@ -26,14 +26,16 @@ class runner : public std::enable_shared_from_this<runner> {
     runner &operator=(const runner &) = delete;
     runner(runner &&) = delete;
     runner &operator=(runner &&) = delete;
-    ~runner() noexcept;
+    ~runner() = default;
 
     static void resolve_symbols();
 
     void run() noexcept(false);
 
     void register_for_rc_notifications();
 
+    void unregister_for_rc_notifications();
+
     [[nodiscard]] bool interrupted() const
     {
         return interrupted_.load(std::memory_order_acquire);