Use X11 protocol directly via libxcb, instead of xhost command (#163)

Use X11 protocol directly via `libxcb`. The `xhost` dependency is no longer needed.

Author: intgr

Cargo.lock

@@ -23,6 +23,7 @@ log = { version = "0.4.20", features = ["std"] }
 shell-words = "1.1.0"
 nix = { version = "0.29.0", default-features = false, features = ["user"] }
 anstyle = "1.0.4"
+xcb = "1.4.0"
 
 [features]
 default = []

Cargo.toml

@@ -10,7 +10,7 @@ ego (a.k.a Alter Ego)
 
 **Ego** is a tool to run Linux desktop applications under a different local user. Currently
 integrates with Wayland, Xorg, PulseAudio and xdg-desktop-portal. You may think of it as `xhost`
-for Wayland and PulseAudio. This is done using filesystem ACLs and `xhost` command.
+for Wayland and PulseAudio. This is done using filesystem ACLs and X11 host access control.
 
 Disclaimer: **DO NOT RUN UNTRUSTED PROGRAMS VIA EGO.** However, using ego is more secure than
 running applications directly under your primary user.
@@ -32,7 +32,7 @@ Ego aims to come with sane defaults and be easy to set up.
 **Requirements:**
 * [Rust & cargo](https://www.rust-lang.org/tools/install)
 * `libacl.so` library (Debian/Ubuntu: libacl1-dev; Fedora: libacl-devel; Arch: acl)
-* `xhost` binary (Debian/Ubuntu: x11-xserver-utils; Fedora: xorg-xhost; Arch: xorg-xhost)
+* `libxcb.so` library (Debian/Ubuntu: libxcb1-dev; Fedora: libxcb-devel; Arch: libxcb)
 
 **Recommended:** (Not needed when using `--sudo` mode, but some desktop functionality may not work).
 * `machinectl` command (Debian/Ubuntu/Fedora: systemd-container; Arch: systemd)
@@ -81,6 +81,9 @@ For sudo, add the following to `/etc/sudoers` (replace `<myname>` with your own
 Changelog
 ---------
 
+##### Unreleased
+* Use X11 protocol directly via `libxcb`. The `xhost` dependency is no longer needed. (#163)
+
 ##### 1.1.7 (2023-06-26)
 * Distro packaging: added tmpfiles.d conf to create missing ego user home directory (#134, fixed issue #131)
 * Ego now detects and warns when target user's home directory does not exist or has wrong ownership (#139)

README.md

@@ -15,6 +15,7 @@ pub struct Args {
     pub command: Vec<String>,
     pub log_level: Level,
     pub method: Option<Method>,
+    pub old_xhost: bool,
 }
 
 pub fn build_cli() -> Command {
@@ -47,6 +48,12 @@ pub fn build_cli() -> Command {
                 .help("Use 'machinectl' but skip xdg-desktop-portal setup"),
         )
         .group(ArgGroup::new("method").args(["sudo", "machinectl", "machinectl-bare"]))
+        .arg(
+            Arg::new("old-xhost")
+                .long("old-xhost")
+                .action(ArgAction::SetTrue)
+                .help("Execute 'xhost' command instead of connecting to X11 directly"),
+        )
         .arg(
             Arg::new("command")
                 .help("Command name and arguments to run (default: user shell)")
@@ -79,6 +86,7 @@ pub fn parse_args<T: Into<OsString> + Clone>(args: impl IntoIterator<Item = T>)
             2 => Level::Debug,
             _ => Level::Trace,
         },
+        old_xhost: matches.get_flag("old-xhost"),
         method: if matches.get_flag("machinectl") {
             Some(Method::Machinectl)
         } else if matches.get_flag("machinectl-bare") {

src/cli.rs

@@ -7,6 +7,7 @@ extern crate simple_error;
 use crate::cli::{parse_args, Method};
 use crate::errors::{print_error, AnyErr, ErrorWithHint};
 use crate::util::{exec_command, have_command, run_command, sd_booted};
+use crate::x11::x11_add_acl;
 use log::{debug, info, log, warn, Level};
 use nix::libc::uid_t;
 use nix::unistd::{Uid, User};
@@ -28,6 +29,7 @@ mod logging;
 #[cfg(test)]
 mod tests;
 mod util;
+mod x11;
 
 #[derive(Clone)]
 struct EgoContext {
@@ -60,7 +62,7 @@ fn main_inner() -> Result<(), AnyErr> {
         Err(msg) => bail!("Error preparing Wayland: {msg}"),
         Ok(ret) => vars.extend(ret),
     }
-    match prepare_x11(&ctx) {
+    match prepare_x11(&ctx, args.old_xhost) {
         Err(msg) => bail!("Error preparing X11: {msg}"),
         Ok(ret) => vars.extend(ret),
     }
@@ -233,17 +235,23 @@ fn prepare_wayland(ctx: &EgoContext) -> Result<Vec<String>, AnyErr> {
     Ok(vec![format!("WAYLAND_DISPLAY={}", path.to_str().unwrap())])
 }
 
-/// Detect `DISPLAY` and run `xhost` to grant permissions.
+/// Detect `DISPLAY` and grant permissions via X11 protocol `ChangeHosts` command
+/// (or run `xhost` command if `--old-xhost` was used).
 /// Return environment vars for `DISPLAY`
-fn prepare_x11(ctx: &EgoContext) -> Result<Vec<String>, AnyErr> {
+fn prepare_x11(ctx: &EgoContext, old_xhost: bool) -> Result<Vec<String>, AnyErr> {
     let display = getenv_optional("DISPLAY")?;
     if display.is_none() {
         debug!("X11: DISPLAY not set, skipping");
         return Ok(vec![]);
     }
 
-    let grant = format!("+si:localuser:{}", ctx.target_user);
-    run_command("xhost", &[grant])?;
+    if old_xhost {
+        warn!("--old-xhost is deprecated. If there are issues with the new method, please report a bug.");
+        let grant = format!("+si:localuser:{}", ctx.target_user);
+        run_command("xhost", &[grant])?;
+    } else {
+        x11_add_acl("localuser", &ctx.target_user)?;
+    }
     // TODO should also test /tmp/.X11-unix/X0 permissions?
 
     Ok(vec![format!("DISPLAY={}", display.unwrap())])

src/main.rs

@@ -10,6 +10,7 @@ Options:
       --sudo             Use 'sudo' to change user
       --machinectl       Use 'machinectl' to change user (default, if available)
       --machinectl-bare  Use 'machinectl' but skip xdg-desktop-portal setup
+      --old-xhost        Execute 'xhost' command instead of connecting to X11 directly
   -v, --verbose...       Verbose output. Use multiple times for more output.
   -h, --help             Print help
   -V, --version          Print version

src/snapshots/ego.help

@@ -11,6 +11,7 @@ use snapbox::{file, Data};
 
 use crate::cli::{build_cli, parse_args, Method};
 use crate::util::have_command;
+use crate::x11::x11_add_acl;
 use crate::{check_user_homedir, get_wayland_socket, EgoContext};
 
 /// `vec![]` constructor that converts arguments to String
@@ -107,6 +108,17 @@ fn wayland_socket() {
     );
 }
 
+#[test]
+fn test_x11_error() {
+    env::remove_var("DISPLAY");
+
+    let err = x11_add_acl("test", "test").unwrap_err();
+    assert_eq!(
+        err.to_string(),
+        "Connection closed, error during parsing display string"
+    );
+}
+
 #[test]
 fn test_cli() {
     build_cli().debug_assert();

src/tests.rs

@@ -0,0 +1,20 @@
+use log::debug;
+use xcb::x::{ChangeHosts, Family, HostMode};
+use xcb::Connection;
+
+use crate::errors::AnyErr;
+
+pub fn x11_add_acl(type_tag: &str, value: &str) -> Result<(), AnyErr> {
+    let (conn, _screen_num) = Connection::connect(None)?;
+
+    debug!("X11: Adding XHost entry SI:{type_tag}:{value}");
+
+    let result = conn.send_and_check_request(&ChangeHosts {
+        mode: HostMode::Insert,
+        family: Family::ServerInterpreted,
+        address: format!("{type_tag}\x00{value}").as_bytes(),
+    });
+    map_err_with!(result, "Error adding XHost entry")?;
+
+    Ok(())
+}

src/x11.rs

@@ -19,7 +19,7 @@ _ego() {
 
     case "${cmd}" in
         ego)
-            opts="-u -v -h -V --user --sudo --machinectl --machinectl-bare --verbose --help --version [command]..."
+            opts="-u -v -h -V --user --sudo --machinectl --machinectl-bare --old-xhost --verbose --help --version [command]..."
             if [[ ${cur} == -* || ${COMP_CWORD} -eq 1 ]] ; then
                 COMPREPLY=( $(compgen -W "${opts}" -- "${cur}") )
                 return 0

varia/ego-completion.bash

@@ -2,6 +2,7 @@ complete -c ego -s u -l user -d 'Specify a username (default: ego)' -r -f -a "(_
 complete -c ego -l sudo -d 'Use \'sudo\' to change user'
 complete -c ego -l machinectl -d 'Use \'machinectl\' to change user (default, if available)'
 complete -c ego -l machinectl-bare -d 'Use \'machinectl\' but skip xdg-desktop-portal setup'
+complete -c ego -l old-xhost -d 'Execute \'xhost\' command instead of connecting to X11 directly'
 complete -c ego -s v -l verbose -d 'Verbose output. Use multiple times for more output.'
 complete -c ego -s h -l help -d 'Print help'
 complete -c ego -s V -l version -d 'Print version'