Add an opt-in filter for host desktop-session variables

RCLOL_FILTER_HOST_ENV=1 makes exec-guest.py drop host session metadata
(WAYLAND_DISPLAY, XDG_SESSION_*, XDG_CURRENT_DESKTOP, GNOME/KDE/GDM,
systemd, SSH agent, terminal, toolkit, Flatpak/Snap/AppImage, exported
shell functions) and set SHELL to the guest's /bin/zsh. It is off by
default; RCLOL_KEEP_HOST_ENV lists names to keep anyway.

Unlike the denylist in #61, the filter runs after the launcher sets its
GPU tuning, keeps everything Darling and the host graphics and audio
libraries read (DISPLAY, XAUTHORITY, XDG_RUNTIME_DIR and the XDG base
directories, D-Bus, PulseAudio/PipeWire/ALSA, DRI_PRIME, MESA_*, __GL_*,
__NV_*, VK_*, LD_PRELOAD for gamemoderun, LD_LIBRARY_PATH), and lives in
one place instead of three.

tests/test_exec_guest.py runs in CI; the launcher check also verifies
that MESA_NO_ERROR=1 and __GL_THREADED_OPTIMIZATIONS=0 reach the guest
with the filter on.

Split from #61.

Co-authored-by: DevWebeloper <[email protected]>
Co-Authored-By: Claude Opus 5.5 <[email protected]>

tools/exec-guest.py

@@ -1,8 +1,47 @@
 #!/usr/bin/env python3
-"""Run a command without the host file descriptors this launcher inherited (anything above stderr)."""
+"""Run a command without the host file descriptors this launcher inherited (anything above stderr).
+
+With RCLOL_FILTER_HOST_ENV=1 it also drops host desktop-session variables first (see
+host_session_variable). RCLOL_KEEP_HOST_ENV lists names to keep anyway, separated by spaces or commas.
+"""
 import os
 import sys
 
+# Desktop-session, service-manager, terminal and packaging metadata that nothing in the guest reads.
+# Everything Darling and the host libraries it loads need is kept: DISPLAY, XAUTHORITY, XCURSOR_*,
+# XDG_RUNTIME_DIR, XDG_DATA_DIRS and the other XDG base directories (the Vulkan loader searches
+# them), DBUS_SESSION_BUS_ADDRESS, PULSE_*, PIPEWIRE_*, ALSA_*, DRI_PRIME, MESA_*, mesa_glthread,
+# __GL_*, __NV_*, __EGL_*, VK_*, LIBGL_*, LD_PRELOAD (gamemoderun) and LD_LIBRARY_PATH.
+SESSION_PREFIXES = (
+    'XDG_SESSION_', 'XDG_SEAT', 'XDG_VTNR', 'XDG_CURRENT_DESKTOP', 'XDG_MENU_PREFIX',
+    'GNOME_', 'KDE_', 'GDM', 'SSH_', 'SYSTEMD_', 'MEMORY_PRESSURE_', 'QT_', 'GTK_', 'GDK_',
+    'GIO_', 'GSETTINGS_', 'GJS_', 'FLATPAK_', 'SNAP_', 'KONSOLE_', 'TERM_PROGRAM', 'BASH_FUNC_',
+)
+SESSION_NAMES = {
+    'WAYLAND_DISPLAY', 'DESKTOP_SESSION', 'DESKTOP_STARTUP_ID', 'SESSION_MANAGER',
+    'INVOCATION_ID', 'JOURNAL_STREAM', 'MANAGERPID', 'MANAGERPIDFDID', 'NOTIFY_SOCKET',
+    'LISTEN_FDS', 'LISTEN_PID', 'LISTEN_FDNAMES', 'COLORTERM', 'VTE_VERSION', 'WINDOWID',
+    'WINDOWPATH', 'CHROME_DESKTOP', 'NO_AT_BRIDGE', 'MOTD_SHOWN', 'SNAP', 'APPIMAGE', 'APPDIR',
+    'OWD', 'VIRTUAL_ENV', 'DEBUGINFOD_URLS', 'LS_COLORS', 'COLORFGBG', 'OLDPWD', 'SHLVL',
+}
+GUEST_SHELL = '/bin/zsh'
+
+
+def host_session_variable(name):
+    return name in SESSION_NAMES or name.startswith(SESSION_PREFIXES)
+
+
+def filter_host_environment(environ):
+    """Return the names removed from environ (a mutable mapping), honoring RCLOL_KEEP_HOST_ENV."""
+    keep = set(environ.get('RCLOL_KEEP_HOST_ENV', '').replace(',', ' ').split())
+    removed = sorted(name for name in environ if host_session_variable(name) and name not in keep)
+    for name in removed:
+        del environ[name]
+    # The host login shell (for example /bin/fish) does not exist in the guest.
+    if 'SHELL' not in keep:
+        environ['SHELL'] = GUEST_SHELL
+    return removed
+
 
 def close_inherited_fds():
     """A terminal, IDE or service manager can leak descriptors; the guest must not inherit them."""
@@ -22,6 +61,8 @@ def close_inherited_fds():
 def main(argv):
     if len(argv) < 2:
         sys.exit('usage: exec-guest.py COMMAND [ARGUMENT]...')
+    if os.environ.get('RCLOL_FILTER_HOST_ENV') == '1':
+        filter_host_environment(os.environ)
     close_inherited_fds()
     os.execvp(argv[1], argv[1:])
 

tools/riot-launcher-offline-check.py

@@ -36,7 +36,8 @@ if record["command"] == "darling":
             return False
     record["fds"] = sorted(fd for fd in map(int, os.listdir("/proc/self/fd")) if is_open(fd))
     record["flags"] = {{key: os.environ.get(key) for key in
-        ("RCLOL_APP_ARG3", "RCLOL_APP_ARG3_SLOT", "RCLOL_UX_ARG2", "RCLOL_UX_ARG2_SLOT", "RCLOL_UX_ARG1", "RCLOL_APP_ARGS", "RCLOL_APP_ARG2", "DYLD_INSERT_LIBRARIES", "DYLD_LIBRARY_PATH", "DYLD_FRAMEWORK_PATH", "DARLING_XSHM_LIBRARY")}}
+        ("RCLOL_APP_ARG3", "RCLOL_APP_ARG3_SLOT", "RCLOL_UX_ARG2", "RCLOL_UX_ARG2_SLOT", "RCLOL_UX_ARG1", "RCLOL_APP_ARGS", "RCLOL_APP_ARG2", "DYLD_INSERT_LIBRARIES", "DYLD_LIBRARY_PATH", "DYLD_FRAMEWORK_PATH", "DARLING_XSHM_LIBRARY",
+         "WAYLAND_DISPLAY", "XAUTHORITY", "DRI_PRIME", "MESA_NO_ERROR", "__GL_THREADED_OPTIMIZATIONS", "SHELL")}}
 with open({str(log)!r}, "a") as output:
     output.write(json.dumps(record) + "\\n")
 '''
@@ -116,7 +117,17 @@ with open({str(log)!r}, "a") as output:
         subprocess.run(["sh", str(launcher)], env=env, check=True, capture_output=True, text=True)
         clean = json.loads(log.read_text().splitlines()[-1])
         assert clean["flags"]["DYLD_INSERT_LIBRARIES"] is None
-        print("LAUNCHER_OFFLINE pass=1 installed=PASS installer=PASS inherited_injection=absent runtime=preserved inherited_fds=closed")
+        # The opt-in host environment filter drops session metadata but never the launcher's GPU tuning.
+        env.update({"RCLOL_FILTER_HOST_ENV": "1", "WAYLAND_DISPLAY": "wayland-0", "XAUTHORITY": "/tmp/xauth",
+                    "DRI_PRIME": "1", "SHELL": "/bin/fish"})
+        env.pop("MESA_NO_ERROR", None)
+        env.pop("__GL_THREADED_OPTIMIZATIONS", None)
+        subprocess.run(["sh", str(launcher)], env=env, check=True, capture_output=True, text=True)
+        filtered = json.loads(log.read_text().splitlines()[-1])["flags"]
+        assert filtered["WAYLAND_DISPLAY"] is None and filtered["SHELL"] == "/bin/zsh", "host session metadata survived"
+        assert (filtered["XAUTHORITY"], filtered["DRI_PRIME"]) == ("/tmp/xauth", "1"), "X11/GPU selection lost"
+        assert (filtered["MESA_NO_ERROR"], filtered["__GL_THREADED_OPTIMIZATIONS"]) == ("1", "0"), "launcher GPU tuning lost"
+        print("LAUNCHER_OFFLINE pass=1 installed=PASS installer=PASS inherited_injection=absent runtime=preserved inherited_fds=closed host_env_filter=PASS")
 
 
 if __name__ == "__main__":