KPIFOCUS: KeeP my Input FOCUS from being stolen by hostile applications

A dirty and brute-force hack into the Gnome Desktop Environment to prevent most applications from stealing the input focus.

Why

Story

1. Imagine that you have a slow laptop. Your tasks today are
   • upgrade system using apt
   • fix bugs in 2 projects
   • play Minecraft
2. Now your laggy system boots up. You clicked Terminal, Visual Studio Code, Minecraft Launcher one by one in the app launcher.
3. Terminal shows up first, you typed sudo apt upgrade -y, sudo asked you for authorization.
4. When you're typing your password, Visual Studio Code popped up and took your focus, now you're typing password into wrong place !
5. You switched manually to Terminal and typed password again. apt is working, you switched back to Visual Studio Code to fix bugs in your project.
6. And then Minecraft Launcher popped up and took focus when you're typing, just voiding the function prototype you've just typed. You clicked 'launch' button, game still took some time to launch, you went back to code.
7. Now Minecraft launched, the window took focus and cover the whole screen. You're so annoyed and smashed at the power button. system reboots.
8. everything above would just replay once your system boots up again.

Complain

1. I believe that it is us human beings who use computers for work, game or whatever else they prefer, rather than computer programs to confuse or 'play' humans. In other words, human control computers, not computers control human. It is true at least in the year 2022 and the past.
2. I have no idea why applications tend to steal input focus from the user, and why window system of OS could allow so. It is disruptive and show no respect to users, I mean human beings, to interrupt them for trivial software events when they're concentrating on one specific application.
3. Many so called famous applications are actually toxic and aggressive, they steal focus on every tiny dialog they show. Below are some applications I've encountered. There must be way way way more.
   • Steam
   • Visual Studio Code
   • Java from OpenJDK (thus most java programs)
   • VirtualBox
   • Wine (aka wine-based Windows applications)
4. Window system is also to blame for giving up focus too easily.
5. There're many GUI toolkits/libraries who make focus stealing their default behavior, such as GLFW. I suspect that Qt, GTK and many others also have this insane default. This makes every application based on them steals focus if the developer is not aware of focus and flip the switch explicitly.

Objective

My desired behavior considering input focus is fairly simple.

1. Input focus should be controlled by the user. NO program except the window system itself could change input focus.
2. Window system should respect the user and change input focus only as user instructed.
3. As a workaround to existing applications, when a window has input focus, it can transfer focus among windows belonging to the same process.
   • Many applications rely on model dialogs to work properly, such as save as dialog or color picker panel of GIMP
   • Applications can mess with their own dialogs once focused, but not other applications' nor when they lose focus. Applications playing around its windows too much would only ruin itself in user's experience.

How

Prerequisites

Again, this is a dirty and brute-force hack into the Gnome Desktop Environment to solve focus-stealing issues. Use this solution AT YOUR OWN RISK. Prerequisites as follows.

• software
  • Ubuntu 20.04 (works on 18.04, but needs manual patching)
  • Gnome-shell desktop environment, Xorg as display server (Wayland works, not fully tested).
  • Being able to install packages & download source code via apt
• knowledge & skills
  • KNOW WHAT YOU ARE DOING
  • Use experience in Gnome Desktop Environment, which is the default for Ubuntu 18.04/20.04
  • Being able to run commands from Terminal
  • Being able to repair your system from TTY in case your window system blow up.
  • Knowledge about Gnome-shell, Mutter, Xorg helps.

common steps

1. Enable source-code-repositories for apt
   • launch Software & Updates, check the Source code checkbox, confirm changes.
   • Alternatively, edit /etc/apt/sources.list, uncomment every line starting with deb-src, then run sudo apt update

Hack mutter

1. Download source code for libmutter-6-0

    cd $PLACE_YOU_WANT_TO_DOWNLOAD_THE_CODE_INTO
   
    # libmutter-2-0 for Ubuntu 18.04
    apt source libmutter-6-0
   
    # directory name starting with 'mutter-', version number may change
    cd mutter-3.36.9/
   

2. Install build dependencies

    sudo apt build-dep libmutter-6-0
   

3. Apply the hack

    # for Ubuntu 18.04, you may need to modify the code manually
    git apply mutter-hack-focal.diff
   

4. Compile hacked libmutter

    DEB_BUILD_OPTIONS=nocheck dpkg-buildpackage -uc -b
   

5. Install the hack

    cd ..
   
    # file staring with 'libmutter-6-0_' and ending with '.deb', version number may change
    sudo dpkg -i libmutter-6-0_3.36.9-0ubuntu0.20.04.2_amd64.deb
   
    # prevent libmutter-6-0 from upgrading
    sudo apt-mark hold libmutter-6-0
   

6. Reboot your system and check the effect.

Hack xserver

1. Download source code for xserver-xorg-core

    cd $PLACE_YOU_WANT_TO_DOWNLOAD_THE_CODE_INTO
   
    apt source xserver-xorg-core
   
    # directory name starting with 'xorg-server-', version number may change
    cd xorg-server-1.20.13/
   

2. Install build dependencies

    sudo apt build-dep xserver-xorg-core
   

3. Apply the hack

    # for Ubuntu 18.04, you may need to modify the code manually
    git apply xserver-hack-focal.diff
   

4. change code if needed

   currently the whitelist for SetInputFocus/GrabDevice is hardedcoded and set to /usr/bin/gnome-shell . If you're not on Ubuntu/Gnome, change this to your window manager binary in file dix/kpifocus.c

5. Compile hacked xserver-xorg-core

    dpkg-buildpackage -uc -b --no-sign
   

6. Install the hack

    cd ..
   
    # file staring with 'xserver-xorg-core_' and ending with '.deb', version number may change
    sudo dpkg -i xserver-xorg-core_1.20.13-1ubuntu1~20.04.9_amd64.deb
   
    # prevent xserver-xorg-core from upgrading
    sudo apt-mark hold xserver-xorg-core
   

7. Reboot your system and check the effect.

Note

Normally you could just proceed up to this point and git rid of focus stealing in most cases. Below are old methods before xserver hack is implemented. They have some downsides and should not be used unless you have a reason. See below for more details.

Hack libx11

Usually the libmutter hack is enough for most applications. the hack below for libx11 mainly blocked Java from stealing focus.
This one is known to be relatively tricky and unstable, and could possibly break several other applications. If in doubt, do not apply this hack.

1. Download source code for libx11-6

    cd $PLACE_YOU_WANT_TO_DOWNLOAD_THE_CODE_INTO
   
    apt source libx11-6
   
    # directory name starting with 'libx11-', version number may change
    cd libx11-1.6.9/
   

2. Install build dependencies

    sudo apt build-dep libx11-6
   

3. Apply the hack

    # for Ubuntu 18.04, you may need to modify the code manually
    git apply libx11-hack-focal.diff
   

4. Compile hacked libx11

    dpkg-buildpackage -uc -b
   

5. Install the hack

    cd ..
   
    # file staring with 'libx11-6_' and ending with '.deb', version number may change
    sudo dpkg -i libx11-6_1.6.9-2ubuntu1.2_amd64.deb
   
    # prevent libx11-6 from upgrading
    sudo apt-mark hold libx11-6
   

6. Do configuration

   • Hack code inside libx11 would reject focus requests other than process whose name matches environment variable X_WINDOW_MANAGER_HOST

   • You should set this variable to the window manager you're using. By default mutter on Ubuntu 18.04/20.04.

   • Since libmutter is hosted in gnome-shell, you should set it to /usr/bin/gnome-shell

       echo 'export X_WINDOW_MANAGER_HOST=/usr/bin/gnome-shell' >> ~/.profile
     

7. Reboot your system and check the effect.

Hack libxcb

The hack below for libxcb mainly blocked VirtualBoxVM from stealing focus & lock the keyboard. This one is known to be tricky and overkill, and could break VirtualBox itself and possibly some other applications. Since the hack code relies on the fact that libmutter does not depend on libxcb to move around focus, so once this condition no longer meets, this hack could effectively lock up or crash the desktop environment even after a normal package upgrade. If in doubt, do not apply this hack. If you do want to try this hack, be ready to recover from a crash at any time in the future.

1. Download source code for libxcb1

    cd $PLACE_YOU_WANT_TO_DOWNLOAD_THE_CODE_INTO
   
    apt source libxcb1
   
    # directory name starting with 'libxcb-', version number may change
    cd libxcb-1.14/
   

2. Install build dependencies

    sudo apt build-dep libxcb1
   

3. Apply the hack

    # for Ubuntu 18.04, you may need to modify the code manually
    git apply libxcb-hack-focal.diff
   

4. Compile hacked libxcb1

    dpkg-buildpackage -uc -b
   

5. Install the hack

    cd ..
   
    # file staring with 'libxcb1_' and ending with '.deb', version number may change
    sudo dpkg -i libxcb1_1.14-2_amd64.deb
   
    # prevent libxcb1 from upgrading
    sudo apt-mark hold libxcb1
   

6. Reboot your system and check the effect.

uninstallation / restore to system defaults

sudo apt install --reinstall xserver-xorg-core libmutter-6-0 libx11-6 libxcb1
sudo apt-mark unhold xserver-xorg-core libmutter-6-0 libx11-6 libxcb1

How to save yourself when window system blew up

1. press CTRL+ALT+F4 to switch to TTY4

   • any TTY without graphical interface works as well, you can even ssh into the system remotely

2. Type your username & password as promoted to login.

3. Type the following command, sudo would request your authorization, type password when asked.

    sudo apt install -y --reinstall xserver-xorg-core libmutter-6-0 libx11-6 libxcb1
    sudo reboot
   

4. Wait for the system to reboot. We've restored to default system libraries, now your window system should start normally.

More details

Known issues & defects

1. You'll notice that after the hack, most application launches without visible window but a notification (if you have not banned that). For example, when you click on downloaded document file in browser, the Document Viewer launches in background, whose window is covered by your browser, and on top bar "Document Viewer" is ready pops up. This is intended since the "bring to front" behavior is actually a focus stealing. The application launches normally, its window is just behind the currently-focused window. You can click on the Dock icon or Alt-Tab to switch to that window. You have to get used to it, or just uninstall this hack since this solution is not for you.
2. Applying mutter hack & xserver hack should be enough for normal use under Xorg. The newly-implemented xserver hack could replace libx11 hack and (mostly) libxcb hack. So don't use libx11 hack, and if you're not using VirtualBox and rely on its input grabbing functionality, don't touch the libxcb hack.
3. Since this hack violates ICCCM/EWMH protocol, some applications may failed to get focus or even crash. I haven't observed this issue on any normal (I mean native) application I've used, but there might be.
4. There're still some applications who could steal focus even with libmutter hack applied. Those toxic and brute programs directly send focus message to Xorg server via either XSetInputFocus from libx11 or xcb_set_input_focus from libxcb.
   • Java from OpenJDK. It calls XSetInputFocus on every dialog it creates. So nearly every java application with a main window would steal your focus forcefully. You can apply the libx11 hack to block this. However some Java dialogs failed to receive inputs after applying this hack.
   • VirtualBox. Actually it's fine for VirtualBoxVM to mess with Xorg. When you're working in a VM, you want your input go directly into that VM, so VirtualBoxVM grabbed keyboard & mouse for you. However it has gone too far. If you have auto capture keyboard setting enabled (which is the default), when VM window first show up or guest OS change resolution, VirtualBoxVM would first request focus via Qt5 framework, which calls xcb_set_input_focus, and then without checking the actual focus window install keyboard & mouse grabs using xcb library (There's actually focus checking logic controlled by a compile-time switch, but it's off in official release. See more details in VirtualBox source code VirtualBox-6.1.36/src/VBox/Frontends/VirtualBox/src/runtime/UIKeyboardHandler.cpp +280 ). Below are behaviors of VirtualBoxVM under different hacks.
     • No hack applied: VirtualBoxVM would forcefully change to workspace it's on & raise itself & steal focus once launched or guest OS change resolution.
     • With libmutter hack applied: workspace & window stacking won't change, but keyboard is grabbed once launched or guest OS change resolution, which means your keyboard suddenly stopped working since it's grabbed into the VM, and you cannot tell why if the VM window isn't visible, you have to press the Host key to release the keyboard grab.
     • With both libmutter and libxcb hack applied: issues above won't appear. However you may have trouble dragging to move/resize VirtualBoxVM window, pressing Host key before dragging sometimes works.
   • Wine. I haven't inspected the source code of wine, but since it acts like a Windows API translator, there must be very crazy code struggling to meet Windows behavior. The result is, after applying the hack, some Windows applications failed to receive inputs or even crash on focus change, some others still steal focus. This also applies to Win32-based games launched using Steam Proton.

Q&A

1. Is the hack safe ?
   • If I said yes, would you believe me? Go and check the code yourself. Everything involved here is open source.
2. I don't know how to install
   • This solution is not intended for people lack of technical background, you need to modify & recompile system core libraries by yourself. You must know certainly what you're doing in every step and be able to repair your system in case of GUI crash. Please do not touch your system if you cannot understand steps above. If you really hate focus stealing and want to rule it out anyway, please have a try in a virtual machine first. Do not risk your system & personal data.
3. When installing package, error occurs like: trying to overwrite shared '/usr/share/doc/libxcb1/changelog.Debian.gz', which is different from other instances of package libxcb1:amd64
   • It seems that the library you compiled yourself is slightly different from the official release. I don't know the actual reason, but since it's just a changelog, I simply delete this file and try install again. You can backup the file if you want to be safer.
4. Why not submit patch/feature-request to respective development groups ?
   • It's actually a hack than a patch. It violates ICCCM/EWMH protocol, mess up the base code and make libraries judge its users, just to introduce weird functionality beneficial to a few people but confuse most normal users if it could ever appear in settings menu.
   • Further more, focus stealing is not a simple problem that could be solved by mutter alone. Cooperation among libmutter, libx11, libxcb, Xorg and possibly other related projects is required. However it is hard to negotiate so many teams to work together on such trivial and confusing feature.
5. What about Wayland ?
   • Hacks above works on Wayland, but some applications still steals focus. Tested on Ubuntu 22.04 LTS .Needs further reading & hacking the mutter code.

Short-term plans & other things

• For Java / VirtualBox / Wine, it makes more sense to modify & recompile them instead of hack into libx11 / libxcb. However, since I don't have time and/or ability to set up their compilation environment & read through their source code, I chose the easier way to hack the system library instead.
• I'm neither a professor in window system nor a hacker. I'm just solving my very specific problem using my experience & technical skills and share my solution in the hope that it will be useful.
• I am fully employed, and have many projects/plans as off-time interests. So I may have little time to push this project forward or I'm just lazy
• English is not my native language. I'm sorry for any misspoken or improper word/sentence.