From 71c83b479335337b25dc331d3fb4a6e29382ceb5 Mon Sep 17 00:00:00 2001
From: Mike Looijmans <mike.looijmans@topic.nl>
Date: Tue, 16 Jan 2024 16:27:43 +0100
Subject: [PATCH] VNCServerST: Add a timeout to pointer button ownership

When one clients holds down a button on the pointer device (probably
dragging something), other clients' attempts at pointer operations
are denied. This yields a sane user experience, but with limits.

When one clients starts dragging, and then his network connection fails,
other clients are denied access to the pointer until the VNC server
finally discovers that the connection is dead and closes it. This can
take about 15 minutes.

Add a timeout to this policy: If we don't hear from the client for 3
seconds, other clients are allowed to control the pointer once more.

This solves the problem that one failing network could make the server
completely deaf to other clients for a long time.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
---
 common/rfb/VNCServerST.cxx | 8 ++++++--
 common/rfb/VNCServerST.h   | 2 ++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/common/rfb/VNCServerST.cxx b/common/rfb/VNCServerST.cxx
index f0cfc31a26..bd29f24361 100644
--- a/common/rfb/VNCServerST.cxx
+++ b/common/rfb/VNCServerST.cxx
@@ -83,6 +83,7 @@ VNCServerST::VNCServerST(const char* name_, SDesktop* desktop_)
   : blHosts(&blacklist), desktop(desktop_), desktopStarted(false),
     blockCounter(0), pb(0), ledState(ledUnknown),
     name(name_), pointerClient(0), clipboardClient(0),
+    pointerClientTime(0),
     comparer(0), cursor(new Cursor(0, 0, Point(), NULL)),
     renderedCursorInvalid(false),
     keyRemapper(&KeyRemapper::defInstance),
@@ -484,14 +485,17 @@ void VNCServerST::keyEvent(uint32_t keysym, uint32_t keycode, bool down)
 void VNCServerST::pointerEvent(VNCSConnectionST* client,
                                const Point& pos, int buttonMask)
 {
+  time_t now = time(0);
   if (rfb::Server::maxIdleTime)
     idleTimer.start(secsToMillis(rfb::Server::maxIdleTime));
 
   // Let one client own the cursor whilst buttons are pressed in order
-  // to provide a bit more sane user experience
-  if ((pointerClient != NULL) && (pointerClient != client))
+  // to provide a bit more sane user experience. But limit the time to prevent
+  // locking out all others when e.g. the network is down.
+  if ((pointerClient != NULL) && (pointerClient != client) && ((now - pointerClientTime) < 3))
     return;
 
+  pointerClientTime = now;
   if (buttonMask)
     pointerClient = client;
   else
diff --git a/common/rfb/VNCServerST.h b/common/rfb/VNCServerST.h
index 028903c982..f688b317ad 100644
--- a/common/rfb/VNCServerST.h
+++ b/common/rfb/VNCServerST.h
@@ -191,6 +191,8 @@ namespace rfb {
     std::list<VNCSConnectionST*> clipboardRequestors;
     std::list<network::Socket*> closingSockets;
 
+    time_t pointerClientTime;
+
     ComparingUpdateTracker* comparer;
 
     Point cursorPos;