Fix UAF when exiting a nested run loop in TabDragContextImpl::OnGestu…

…reEvent.

OnGestureEvent may call ContinueDrag, which may run a nested run loop. After the nested run loop returns, multiple seconds of time may have passed, and the world may be in a very different state; in particular, the window that contains this TabDragContext may have closed.

This CL checks if this has happened, and returns early in that case.

Bug: 1453465
Change-Id: I6095c0afeb5aa5f422717f1bbd93b96175e52afa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4657527
Reviewed-by: Darryl James <dljames@chromium.org>
Commit-Queue: Taylor Bergquist <tbergquist@chromium.org>
Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1164449}

chrome/browser/ui/views/tabs/fake_tab_slot_controller.cc

@@ -43,6 +43,12 @@ bool FakeTabSlotController::IsFocusInTabs() const {
   return false;
 }
 
+TabSlotController::Liveness FakeTabSlotController::ContinueDrag(
+    views::View* view,
+    const ui::LocatedEvent& event) {
+  return Liveness::kAlive;
+}
+
 bool FakeTabSlotController::EndDrag(EndDragReason reason) {
   return false;
 }

chrome/browser/ui/views/tabs/fake_tab_slot_controller.h

@@ -60,8 +60,8 @@ class FakeTabSlotController : public TabSlotController {
       TabSlotView* source,
       const ui::LocatedEvent& event,
       const ui::ListSelectionModel& original_selection) override {}
-  void ContinueDrag(views::View* view, const ui::LocatedEvent& event) override {
-  }
+  Liveness ContinueDrag(views::View* view,
+                        const ui::LocatedEvent& event) override;
   bool EndDrag(EndDragReason reason) override;
   Tab* GetTabAt(const gfx::Point& point) override;
   const Tab* GetAdjacentTab(const Tab* tab, int offset) override;

chrome/browser/ui/views/tabs/tab_slot_controller.h

@@ -49,6 +49,8 @@ class TabSlotController {
     kEvent
   };
 
+  enum class Liveness { kAlive, kDeleted };
+
   virtual const ui::ListSelectionModel& GetSelectionModel() const = 0;
 
   // Returns the tab at |index|.
@@ -126,9 +128,12 @@ class TabSlotController {
       const ui::LocatedEvent& event,
       const ui::ListSelectionModel& original_selection) = 0;
 
-  // Continues dragging a Tab.
-  virtual void ContinueDrag(views::View* view,
-                            const ui::LocatedEvent& event) = 0;
+  // Continues dragging a Tab. May enter a nested event loop - returns
+  // Liveness::kDeleted if `this` was destroyed during this nested event loop,
+  // and Liveness::kAlive if `this` is still alive.
+  [[nodiscard]] virtual Liveness ContinueDrag(
+      views::View* view,
+      const ui::LocatedEvent& event) = 0;
 
   // Ends dragging a Tab. Returns whether the tab has been destroyed.
   virtual bool EndDrag(EndDragReason reason) = 0;

chrome/browser/ui/views/tabs/tab_strip.cc

@@ -178,7 +178,7 @@ class TabStrip::TabDragContextImpl : public TabDragContext,
   }
 
   bool OnMouseDragged(const ui::MouseEvent& event) override {
-    ContinueDrag(this, event);
+    (void)ContinueDrag(this, event);
     return true;
   }
 
@@ -189,6 +189,7 @@ class TabStrip::TabDragContextImpl : public TabDragContext,
   void OnMouseCaptureLost() override { EndDrag(END_DRAG_CAPTURE_LOST); }
 
   void OnGestureEvent(ui::GestureEvent* event) override {
+    Liveness tabstrip_alive = Liveness::kAlive;
     switch (event->type()) {
       case ui::ET_GESTURE_SCROLL_END:
       case ui::ET_SCROLL_FLING_START:
@@ -202,7 +203,8 @@ class TabStrip::TabDragContextImpl : public TabDragContext,
       }
 
       case ui::ET_GESTURE_SCROLL_UPDATE:
-        ContinueDrag(this, *event);
+        // N.B. !! ContinueDrag may enter a nested run loop !!
+        tabstrip_alive = ContinueDrag(this, *event);
         break;
 
       case ui::ET_GESTURE_TAP_DOWN:
@@ -214,6 +216,12 @@ class TabStrip::TabDragContextImpl : public TabDragContext,
     }
     event->SetHandled();
 
+    // If tabstrip was destroyed (during ContinueDrag above), return early to
+    // avoid UAF below.
+    if (tabstrip_alive == Liveness::kDeleted) {
+      return;
+    }
+
     // TabDragContext gets event capture as soon as a drag session begins, which
     // precludes TabStrip from ever getting events like tap or long tap. Forward
     // this on to TabStrip so it can respond to those events.
@@ -302,20 +310,21 @@ class TabStrip::TabDragContextImpl : public TabDragContext,
       std::move(drag_controller_set_callback_).Run(drag_controller_.get());
   }
 
-  void ContinueDrag(views::View* view, const ui::LocatedEvent& event) {
-    if (drag_controller_.get() &&
-        drag_controller_->event_source() == EventSourceFromEvent(event)) {
-      gfx::Point screen_location(event.location());
-      views::View::ConvertPointToScreen(view, &screen_location);
+  [[nodiscard]] Liveness ContinueDrag(views::View* view,
+                                      const ui::LocatedEvent& event) {
+    if (!drag_controller_.get() ||
+        drag_controller_->event_source() != EventSourceFromEvent(event)) {
+      return Liveness::kAlive;
+    }
 
-      // Note: |tab_strip_| can be destroyed during drag, also destroying
-      // |this|.
-      base::WeakPtr<TabDragContext> weak_ptr(weak_factory_.GetWeakPtr());
-      drag_controller_->Drag(screen_location);
+    gfx::Point screen_location(event.location());
+    views::View::ConvertPointToScreen(view, &screen_location);
 
-      if (!weak_ptr)
-        return;
-    }
+    // Note: `tab_strip_` can be destroyed during drag, also destroying `this`.
+    base::WeakPtr<TabDragContext> weak_ptr(weak_factory_.GetWeakPtr());
+    drag_controller_->Drag(screen_location);
+
+    return weak_ptr ? Liveness::kAlive : Liveness::kDeleted;
   }
 
   bool EndDrag(EndDragReason reason) {
@@ -1593,8 +1602,10 @@ void TabStrip::MaybeStartDrag(
   drag_context_->MaybeStartDrag(source, event, original_selection);
 }
 
-void TabStrip::ContinueDrag(views::View* view, const ui::LocatedEvent& event) {
-  drag_context_->ContinueDrag(view, event);
+TabSlotController::Liveness TabStrip::ContinueDrag(
+    views::View* view,
+    const ui::LocatedEvent& event) {
+  return drag_context_->ContinueDrag(view, event);
 }
 
 bool TabStrip::EndDrag(EndDragReason reason) {

chrome/browser/ui/views/tabs/tab_strip.h

@@ -278,7 +278,8 @@ class TabStrip : public views::View,
       TabSlotView* source,
       const ui::LocatedEvent& event,
       const ui::ListSelectionModel& original_selection) override;
-  void ContinueDrag(views::View* view, const ui::LocatedEvent& event) override;
+  [[nodiscard]] Liveness ContinueDrag(views::View* view,
+                                      const ui::LocatedEvent& event) override;
   bool EndDrag(EndDragReason reason) override;
   Tab* GetTabAt(const gfx::Point& point) override;
   const Tab* GetAdjacentTab(const Tab* tab, int offset) override;