[Base] Refactor POSIX timers, fix user-after-free

Since timer_delete does not clean up already queued signals, signal info
data needs to be retained after timer deletion and object destruction in
order to circumvent use-after-free bugs.

src/xenia/base/threading_posix.cc

@@ -10,7 +10,7 @@
 #include "xenia/base/threading.h"
 
 #include "xenia/base/assert.h"
-#include "xenia/base/logging.h"
+#include "xenia/base/delay_scheduler.h"
 #include "xenia/base/platform.h"
 
 #include <pthread.h>
@@ -23,7 +23,6 @@
 #include <unistd.h>
 #include <array>
 #include <cstddef>
-#include <cstring>
 #include <ctime>
 #include <memory>
 
@@ -79,6 +78,47 @@ void AndroidShutdown() {
 }
 #endif
 
+// This is separately allocated for each (`HighResolution`)`Timer` object. It
+// will be cleaned up some time (`timers_garbage_collector_delay`) after the
+// posix timer was canceled because posix `timer_delete(...)` does not remove
+// pending timer signals.
+// https://stackoverflow.com/questions/49756114/linux-timer-pending-signal
+struct timer_callback_info_t {
+  std::atomic_bool disarmed;
+#if !XE_HAS_SIGEV_THREAD_ID
+  pthread_t target_thread;
+#endif
+  std::function<void()> callback;
+  void* userdata;
+
+  timer_callback_info_t(std::function<void()> callback)
+      : disarmed(false),
+#if !XE_HAS_SIGEV_THREAD_ID
+        target_thread(),
+#endif
+        callback(callback),
+        userdata(nullptr) {
+  }
+};
+
+// GC for timer signal info structs:
+constexpr uint_fast8_t timers_garbage_collector_scale_ =
+#if XE_HAS_SIGEV_THREAD_ID
+    1;
+#else
+    2;
+#endif
+DelayScheduler<timer_callback_info_t> timers_garbage_collector_(
+    512 * timers_garbage_collector_scale_,
+    [](timer_callback_info_t* info) {
+      assert_not_null(info);
+      delete info;
+    },
+    true);
+// Delay we have to assume it takes to clear all pending signals (maximum):
+constexpr auto timers_garbage_collector_delay =
+    std::chrono::milliseconds(100 * timers_garbage_collector_scale_);
+
 template <typename _Rep, typename _Period>
 inline timespec DurationToTimeSpec(
     std::chrono::duration<_Rep, _Period> duration) {
@@ -195,9 +235,20 @@ bool SetTlsValue(TlsHandle handle, uintptr_t value) {
 class PosixHighResolutionTimer : public HighResolutionTimer {
  public:
   explicit PosixHighResolutionTimer(std::function<void()> callback)
-      : callback_(std::move(callback)), valid_(false) {}
+      : valid_(false) {
+    callback_info_ = new timer_callback_info_t(std::move(callback));
+  }
   ~PosixHighResolutionTimer() override {
-    if (valid_) timer_delete(timer_);
+    if (valid_) {
+      callback_info_->disarmed = true;
+      timer_delete(timerid_);
+      // Deliberately leaks memory when wait queue is full instead of blogs,
+      // check logs
+      static_cast<void>(timers_garbage_collector_.TryScheduleAfter(
+          callback_info_, timers_garbage_collector_delay));
+    } else {
+      delete callback_info_;
+    }
   }
 
   bool Initialize(std::chrono::milliseconds period) {
@@ -216,20 +267,23 @@ class PosixHighResolutionTimer : public HighResolutionTimer {
     callback_info_->target_thread = pthread_self();
 #endif
     sev.sigev_signo = GetSystemSignal(SignalType::kHighResolutionTimer);
-    sev.sigev_value.sival_ptr = (void*)&callback_;
+    sev.sigev_value.sival_ptr = callback_info_;
-    if (timer_create(CLOCK_MONOTONIC, &sev, &timer_) == -1) return false;
+    if (timer_create(CLOCK_MONOTONIC, &sev, &timerid_) == -1) return false;
 
     // Start timer
     itimerspec its{};
     its.it_value = DurationToTimeSpec(period);
     its.it_interval = its.it_value;
-    valid_ = timer_settime(timer_, 0, &its, nullptr) != -1;
+    valid_ = timer_settime(timerid_, 0, &its, nullptr) != -1;
+    if (!valid_) {
+      timer_delete(timerid_);
+    }
     return valid_;
   }
 
  private:
-  std::function<void()> callback_;
+  timer_callback_info_t* callback_info_;
-  timer_t timer_;
+  timer_t timerid_;
   bool valid_;  // all values for timer_t are legal so we need this
 };
 
@@ -441,28 +495,34 @@ template <>
 class PosixCondition<Timer> : public PosixConditionBase {
  public:
   explicit PosixCondition(bool manual_reset)
-      : callback_(),
+      : timer_(nullptr),
-        timer_(nullptr),
+        callback_info_(nullptr),
         signal_(false),
         manual_reset_(manual_reset) {}
 
   virtual ~PosixCondition() { Cancel(); }
 
   bool Signal() override {
-    CompletionRoutine();
+    std::lock_guard<std::mutex> lock(mutex_);
+    signal_ = true;
+    cond_.notify_all();
     return true;
   }
 
   // TODO(bwrsandman): due_times of under 1ms deadlock under travis
+  // TODO(joellinn): This is likely due to deadlock on mutex_ if Signal() is
+  // called from signal_handler running in Thread A while thread A was still in
+  // Set(...) routine inside the lock
   bool Set(std::chrono::nanoseconds due_time, std::chrono::milliseconds period,
            std::function<void()> opt_callback = nullptr) {
-    std::lock_guard<std::mutex> lock(mutex_);
+    Cancel();
 
-    callback_ = std::move(opt_callback);
+    std::lock_guard<std::mutex> lock(mutex_);
+    callback_info_ = new timer_callback_info_t(std::move(opt_callback));
+    callback_info_->userdata = this;
     signal_ = false;
 
     // Create timer
-    if (timer_ == nullptr) {
     sigevent sev{};
 #if XE_HAS_SIGEV_THREAD_ID
     sev.sigev_notify = SIGEV_SIGNAL | SIGEV_THREAD_ID;
@@ -472,8 +532,10 @@ class PosixCondition<Timer> : public PosixConditionBase {
     callback_info_->target_thread = pthread_self();
 #endif
     sev.sigev_signo = GetSystemSignal(SignalType::kTimer);
-      sev.sigev_value.sival_ptr = this;
+    sev.sigev_value.sival_ptr = callback_info_;
-      if (timer_create(CLOCK_MONOTONIC, &sev, &timer_) == -1) return false;
+    if (timer_create(CLOCK_MONOTONIC, &sev, &timer_) == -1) {
+      delete callback_info_;
+      return false;
     }
 
     // Start timer
@@ -483,26 +545,16 @@ class PosixCondition<Timer> : public PosixConditionBase {
     return timer_settime(timer_, 0, &its, nullptr) == 0;
   }
 
-  void CompletionRoutine() {
-    // As the callback may reset the timer, store local.
-    std::function<void()> callback;
-    {
-      std::lock_guard<std::mutex> lock(mutex_);
-      // Store callback
-      if (callback_) callback = callback_;
-      signal_ = true;
-      cond_.notify_all();
-    }
-    // Call callback
-    if (callback) callback();
-  }
-
   bool Cancel() {
     std::lock_guard<std::mutex> lock(mutex_);
     bool result = true;
     if (timer_) {
+      callback_info_->disarmed = true;
       result = timer_delete(timer_) == 0;
       timer_ = nullptr;
+      static_cast<void>(timers_garbage_collector_.TryScheduleAfter(
+          callback_info_, timers_garbage_collector_delay));
+      callback_info_ = nullptr;
     }
     return result;
   }
@@ -518,8 +570,8 @@ class PosixCondition<Timer> : public PosixConditionBase {
       signal_ = false;
     }
   }
-  std::function<void()> callback_;
   timer_t timer_;
+  timer_callback_info_t* callback_info_;
   volatile bool signal_;
   const bool manual_reset_;
 };
@@ -1202,15 +1254,50 @@ static void signal_handler(int signal, siginfo_t* info, void* /*context*/) {
   switch (GetSystemSignalType(signal)) {
     case SignalType::kHighResolutionTimer: {
       assert_not_null(info->si_value.sival_ptr);
-      auto callback =
+      auto timer_info =
-          *static_cast<std::function<void()>*>(info->si_value.sival_ptr);
+          reinterpret_cast<timer_callback_info_t*>(info->si_value.sival_ptr);
-      callback();
+      if (!timer_info->disarmed) {
+#if XE_HAS_SIGEV_THREAD_ID
+        {
+#else
+        if (pthread_self() != timer_info->target_thread) {
+          sigval info_inner{};
+          info_inner.sival_ptr = timer_info;
+          const auto queueres = pthread_sigqueue(
+              timer_info->target_thread,
+              GetSystemSignal(SignalType::kHighResolutionTimer), info_inner);
+          assert_zero(queueres);
+        } else {
+#endif
+          timer_info->callback();
+        }
+      }
     } break;
     case SignalType::kTimer: {
       assert_not_null(info->si_value.sival_ptr);
-      auto pTimer =
+      auto timer_info =
-          static_cast<PosixCondition<Timer>*>(info->si_value.sival_ptr);
+          reinterpret_cast<timer_callback_info_t*>(info->si_value.sival_ptr);
-      pTimer->CompletionRoutine();
+      if (!timer_info->disarmed) {
+        assert_not_null(timer_info->userdata);
+        auto timer = static_cast<PosixCondition<Timer>*>(timer_info->userdata);
+#if XE_HAS_SIGEV_THREAD_ID
+        {
+#else
+        if (pthread_self() != timer_info->target_thread) {
+          sigval info_inner{};
+          info_inner.sival_ptr = timer_info;
+          const auto queueres =
+              pthread_sigqueue(timer_info->target_thread,
+                               GetSystemSignal(SignalType::kTimer), info_inner);
+          assert_zero(queueres);
+        } else {
+#endif
+          timer->Signal();
+          if (timer_info->callback) {
+            timer_info->callback();
+          }
+        }
+      }
     } break;
     case SignalType::kThreadSuspend: {
       assert_not_null(current_thread_);