Faking uinput: mount additional virtual devices without breaking container isolation

[ABeltramo]

Still a draft, will update this when I've got something that works

Implements #81

[ABeltramo]

Status

We can correctly intercept when Steam Input tries to create a virtual device, but we can't mknod the corresponding /dev/input/eventX device node from the host since we don't have enough permission when running as the default retro user.

To properly fix this I guess we could either:

• Add mknod permissions to retro (how? See tests below..)
• Add a simple CLI util, setcap cap_mknod+ep to it, then system("/sudo_mknod /dev/...")
• Add a root running daemon inside the container that when pinged by our ld preloaded lib will do the mknod (+ fake_udev and whatever else will be needed)
• Open a bidirectional socket to Wolf so that we can intercept that and do docker exec -u root mknod ...

What I've tried so far

Build libfake_uinput.so

cmake --target fake_uinput

and libfake-uinput-32.so

cmake -DFAKE_UINPUT_32BIT=ON --target fake_uinput

Change config.toml:

mounts = [
  "/tmp/libfake_uinput.so:/usr/lib/x86_64-linux-gnu/fake-uinput.so:rw",
  "/tmp/libfake-uinput-32.so:/usr/lib/i386-linux-gnu/fake-uinput.so:rw",
  "/tmp/steam-startup.sh:/etc/cont-init.d/99-steam.sh:ro"
]
env = [
  "PROTON_LOG=1",
  "RUN_SWAY=true",
  "GOW_REQUIRED_DEVICES=/dev/input/* /dev/dri/* /dev/nvidia* /dev/uinput",
  "LD_PRELOAD=/usr/$LIB/fake-uinput.so"
]
devices = ["/dev/uinput:/dev/uinput"]

/tmp/steam-startup.sh:

#!/bin/bash
set -e

# Add mknod capability for Steam
setcap 'cap_mknod=eip' /usr/games/steam

# Allow user to mknod under /dev/input
mkdir -p /dev/input
chown ${PUID}:${PGID} /dev/input

cat .steam/debian-installation/logs/console-linux.txt
...
[fake-uinput] Intercepted UI_DEV_CREATE ioctl call
[fake-uinput] Error creating device node: Operation not permitted
[fake-uinput] Error creating device node: Operation not permitted
...

I've also tried setting cap_mknod to /home/retro/.steam/debian-installation/ubuntu12_32/reaper (and steam in the same subfolder) without success. Even tried with setcap all=eip it doesn't seem to have an effect.