Support for flatpak and GNOME Software in Realms

When a realm has enabled 'use-flatpak' a .desktop file for GNOME
Software will be automatically generated while that realm is running.

This .desktop file will launch GNOME Software from Citadel inside a
bubblewrap sandbox. The sandbox has been prepared so that GNOME
Software will install flatpak applications into a directory that belongs
to the realm associated with the .desktop file.

When a realm has enabled 'use-flatpak' this directory will be bind
mounted (read-only) into the root filesystem of the realm so that
applications installed by GNOME Software are visible and can be launched.

Cargo.toml

@@ -1,5 +1,5 @@
 [workspace]
-members = ["citadel-realms", "citadel-installer-ui", "citadel-tool", "realmsd", "realm-config-ui" ]
+members = ["citadel-realms", "citadel-installer-ui", "citadel-tool", "realmsd", "realm-config-ui", "launch-gnome-software" ]
 [profile.release]
 lto = true
 codegen-units = 1

citadel-tool/src/sync/desktop_sync.rs

@@ -99,7 +99,7 @@ impl DesktopFileSync {
     }
 
     fn collect_source_files(&mut self,  directory: impl AsRef<Path>) -> Result<()> {
-        let mut directory = Realms::current_realm_symlink().join(directory.as_ref());
+        let mut directory = self.realm.run_path().join(directory.as_ref());
         directory.push("share/applications");
         if directory.exists() {
             util::read_directory(&directory, |dent| {
@@ -126,7 +126,11 @@ impl DesktopFileSync {
     }
 
     fn remove_missing_target_files(&mut self) -> Result<()> {
-        let sources = self.source_filenames();
+        let mut sources = self.source_filenames();
+        // If flatpak is enabled, don't remove the generated GNOME Software desktop file
+        if self.realm.config().flatpak() {
+            sources.insert(format!("realm-{}.org.gnome.Software.desktop", self.realm.name()));
+        }
         let prefix = format!("realm-{}.", self.realm.name());
         util::read_directory(Self::CITADEL_APPLICATIONS, |dent| {
             if let Some(filename) = dent.file_name().to_str() {
@@ -182,7 +186,9 @@ impl DesktopFileSync {
 
     fn sync_item(&self, item: &DesktopItem) -> Result<()> {
         let mut dfp = DesktopFileParser::parse_from_path(&item.path, "/usr/libexec/citadel-run ")?;
-        if dfp.is_showable() {
+        // When use-flatpak is enabled a gnome-software desktop file will be generated
+        let flatpak_gs_hide = dfp.filename() == "org.gnome.Software.desktop" && self.realm.config().flatpak();
+        if dfp.is_showable() && !flatpak_gs_hide {
             self.sync_item_icon(&mut dfp);
             dfp.write_to_dir(Self::CITADEL_APPLICATIONS, Some(&self.realm))?;
         } else {

citadel-tool/src/sync/icons.rs

@@ -4,7 +4,6 @@ use std::path::{Path, PathBuf};
 
 use libcitadel::{Result, util, Realm};
 use std::cell::{RefCell, Cell};
-use std::fs;
 use crate::sync::desktop_file::DesktopFile;
 use crate::sync::REALM_BASE_PATHS;
 

citadel-tool/src/sync/mod.rs

@@ -14,7 +14,7 @@ fn has_arg(args: &[String], arg: &str) -> bool {
 
 pub const REALM_BASE_PATHS:&[&str]  = &[
     "rootfs/usr",
-    "rootfs/var/lib/flatpak/exports",
+    "flatpak/exports",
     "home/.local",
     "home/.local/share/flatpak/exports"
 ];

launch-gnome-software/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "launch-gnome-software"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+libcitadel = { path = "../libcitadel" }
+anyhow = "1.0"

launch-gnome-software/src/main.rs

@@ -0,0 +1,67 @@
+use std::env;
+
+use libcitadel::{Logger, LogLevel, Realm, Realms, util};
+use libcitadel::flatpak::GnomeSoftwareLauncher;
+
+use anyhow::{bail, Result};
+
+
+fn realm_arg() -> Option<String> {
+    let mut args = env::args();
+    while let Some(arg) = args.next() {
+        if arg == "--realm" {
+            return args.next();
+        }
+    }
+    None
+}
+
+fn choose_realm() -> Result<Realm> {
+    let mut realms = Realms::load()?;
+    if let Some(realm_name) = realm_arg() {
+        match realms.by_name(&realm_name) {
+            None => bail!("realm '{}' not found", realm_name),
+            Some(realm) => return Ok(realm),
+        }
+    }
+    let realm = match realms.current() {
+        Some(realm) => realm,
+        None => bail!("no current realm"),
+    };
+
+    Ok(realm)
+}
+
+fn has_arg(arg: &str) -> bool {
+    env::args()
+        .skip(1)
+        .any(|s| s == arg)
+}
+
+fn launch() -> Result<()> {
+    let realm = choose_realm()?;
+    if !util::is_euid_root() {
+        bail!("Must be run with root euid");
+    }
+    let mut launcher = GnomeSoftwareLauncher::new(realm)?;
+
+    if has_arg("--quit") {
+        launcher.quit()?;
+    } else {
+        if has_arg("--shell") {
+            launcher.set_run_shell();
+        }
+        launcher.launch()?;
+    }
+    Ok(())
+}
+
+fn main() {
+    if has_arg("--verbose") {
+        Logger::set_log_level(LogLevel::Verbose);
+    }
+
+    if let Err(err) = launch() {
+        eprintln!("Error: {}", err);
+    }
+}

libcitadel/Cargo.toml

@@ -10,6 +10,7 @@ nix = "0.17.0"
 toml = "0.5"
 serde = "1.0"
 serde_derive = "1.0"
+serde_json = "=1.0.1"
 lazy_static = "1.4"
 sodiumoxide = "0.2"
 hex = "0.4"

libcitadel/src/flatpak/bubblewrap.rs

@@ -0,0 +1,221 @@
+use std::ffi::OsStr;
+use std::{fs, io};
+use std::fs::File;
+use std::os::fd::AsRawFd;
+use std::os::unix::process::CommandExt;
+use std::path::Path;
+use std::process::Command;
+
+use crate::{Logger, LogLevel, Result, verbose};
+
+const BWRAP_PATH: &str = "/usr/libexec/flatpak-bwrap";
+
+pub struct BubbleWrap {
+    command: Command,
+}
+
+impl BubbleWrap {
+
+    pub fn new() -> Self {
+        BubbleWrap {
+            command: Command::new(BWRAP_PATH),
+        }
+    }
+
+    fn add_arg<S: AsRef<OsStr>>(&mut self, arg: S) -> &mut Self {
+        self.command.arg(arg);
+        self
+    }
+
+    fn add_args<S: AsRef<OsStr>>(&mut self, args: &[S]) -> &mut Self {
+        for arg in args {
+            self.add_arg(arg.as_ref());
+        }
+        self
+    }
+
+    pub fn ro_bind(&mut self, path_list: &[&str]) -> &mut Self {
+        for &path in path_list {
+            self.add_args(&["--ro-bind", path, path]);
+        }
+        self
+    }
+
+    pub fn ro_bind_to(&mut self, src: &str, dest: &str) -> &mut Self {
+        self.add_args(&["--ro-bind", src, dest])
+    }
+
+    pub fn bind_to(&mut self, src: &str, dest: &str) -> &mut Self {
+        self.add_args(&["--bind", src, dest])
+    }
+
+    pub fn create_dirs(&mut self, dir_list: &[&str]) -> &mut Self {
+        for &dir in dir_list {
+            self.add_args(&["--dir", dir]);
+        }
+        self
+    }
+
+    pub fn create_symlinks(&mut self, links: &[(&str, &str)]) -> &mut Self {
+        for (src,dest) in links {
+            self.add_args(&["--symlink", src, dest]);
+        }
+        self
+    }
+
+    pub fn mount_dev(&mut self) -> &mut Self {
+        self.add_args(&["--dev", "/dev"])
+    }
+
+    pub fn mount_proc(&mut self) -> &mut Self {
+        self.add_args(&["--proc", "/proc"])
+    }
+
+    pub fn dev_bind(&mut self, path: &str) -> &mut Self {
+        self.add_args(&["--dev-bind", path, path])
+    }
+
+    pub fn clear_env(&mut self) -> &mut Self {
+        self.add_arg("--clearenv")
+    }
+
+    pub fn set_env_list(&mut self, env_list: &[&str]) -> &mut Self {
+        for line in env_list {
+            if let Some((k,v)) = line.split_once("=") {
+                self.add_args(&["--setenv", k, v]);
+            } else {
+                eprintln!("Warning: environment variable '{}' does not have = delimiter. Ignoring", line);
+            }
+        }
+        self
+    }
+
+    pub fn unshare_all(&mut self) -> &mut Self {
+        self.add_arg("--unshare-all")
+    }
+
+    pub fn share_net(&mut self) -> &mut Self {
+        self.add_arg("--share-net")
+    }
+
+    pub fn log_command(&self) {
+        let mut buffer = String::new();
+        verbose!("{}", BWRAP_PATH);
+        for arg in self.command.get_args() {
+            if let Some(s) = arg.to_str() {
+                if s.starts_with("-") {
+                    if !buffer.is_empty() {
+                        verbose!("    {}", buffer);
+                        buffer.clear();
+                    }
+                }
+                if !buffer.is_empty() {
+                    buffer.push(' ');
+                }
+                buffer.push_str(s);
+            }
+        }
+        if !buffer.is_empty() {
+            verbose!("    {}", buffer);
+        }
+    }
+
+    pub fn status_file(&mut self, status_file: &File) -> &mut Self {
+        // Rust sets O_CLOEXEC when opening files so we create
+        // a new descriptor that will remain open across exec()
+        let dup_fd = unsafe {
+            libc::dup(status_file.as_raw_fd())
+        };
+        if dup_fd == -1 {
+            warn!("Failed to dup() status file descriptor: {}", io::Error::last_os_error());
+            warn!("Skipping --json-status-fd argument");
+            self
+        } else {
+            self.add_arg("--json-status-fd")
+                .add_arg(dup_fd.to_string())
+        }
+    }
+
+    pub fn launch<S: AsRef<OsStr>>(&mut self, cmd: &[S]) -> Result<()> {
+        if Logger::is_log_level(LogLevel::Verbose) {
+            self.log_command();
+            let s = cmd.iter().map(|s| format!("{} ", s.as_ref().to_str().unwrap())).collect::<String>();
+            verbose!("    {}", s)
+        }
+        self.add_args(cmd);
+        let err = self.command.exec();
+        bail!("failed to exec bubblewrap: {}", err);
+    }
+}
+
+#[derive(Deserialize,Clone)]
+#[serde(rename_all="kebab-case")]
+pub struct BubbleWrapRunningStatus {
+    pub child_pid: u64,
+    pub cgroup_namespace: u64,
+    pub ipc_namespace: u64,
+    pub mnt_namespace: u64,
+    pub pid_namespace: u64,
+    pub uts_namespace: u64,
+}
+
+#[derive(Deserialize,Clone)]
+#[serde(rename_all="kebab-case")]
+pub struct BubbleWrapExitStatus {
+    pub exit_code: u32,
+}
+
+#[derive(Clone)]
+pub struct BubbleWrapStatus {
+    running: BubbleWrapRunningStatus,
+    exit: Option<BubbleWrapExitStatus>,
+}
+
+impl BubbleWrapStatus {
+    pub fn parse_file(path: impl AsRef<Path>) -> Result<Option<Self>> {
+        if !path.as_ref().exists() {
+            return Ok(None)
+        }
+
+        let s = fs::read_to_string(path)
+            .map_err(context!("error reading status file"))?;
+
+        let mut lines = s.lines();
+        let running = match lines.next() {
+            None => return Ok(None),
+            Some(s) => serde_json::from_str::<BubbleWrapRunningStatus>(s)
+                .map_err(context!("failed to parse status line ({})", s))?
+        };
+
+        let exit = match lines.next() {
+            None => None,
+            Some(s) => Some(serde_json::from_str::<BubbleWrapExitStatus>(s)
+                .map_err(context!("failed to parse exit line ({})", s))?)
+        };
+
+        Ok(Some(BubbleWrapStatus {
+            running,
+            exit
+        }))
+    }
+
+    pub fn is_running(&self) -> bool {
+        self.exit.is_none()
+    }
+
+    pub fn running_status(&self) -> &BubbleWrapRunningStatus {
+        &self.running
+    }
+
+    pub fn child_pid(&self) -> u64 {
+        self.running.child_pid
+    }
+
+    pub fn pid_namespace(&self) -> u64 {
+        self.running.pid_namespace
+    }
+
+    pub fn exit_status(&self) -> Option<&BubbleWrapExitStatus> {
+        self.exit.as_ref()
+    }
+}

libcitadel/src/flatpak/launcher.rs

@@ -0,0 +1,259 @@
+use std::{fs, io};
+use std::fs::File;
+use std::os::unix::fs::FileTypeExt;
+use std::os::unix::prelude::CommandExt;
+use std::path::{Path, PathBuf};
+use std::process::Command;
+
+use crate::{Realm, Result, util};
+use crate::flatpak::{BubbleWrap, BubbleWrapStatus, SANDBOX_STATUS_FILE_DIRECTORY, SandboxStatus};
+use crate::flatpak::netns::NetNS;
+
+
+const FLATPAK_PATH: &str = "/usr/bin/flatpak";
+
+const ENVIRONMENT: &[&str; 7] = &[
+    "HOME=/home/citadel",
+    "USER=citadel",
+    "XDG_RUNTIME_DIR=/run/user/1000",
+    "XDG_DATA_DIRS=/home/citadel/.local/share/flatpak/exports/share:/usr/share",
+    "TERM=xterm-256color",
+    "GTK_A11Y=none",
+    "FLATPAK_USER_DIR=/home/citadel/realm-flatpak",
+];
+
+const FLATHUB_URL: &str = "https://dl.flathub.org/repo/flathub.flatpakrepo";
+
+pub struct GnomeSoftwareLauncher {
+    realm: Realm,
+    status: Option<BubbleWrapStatus>,
+    netns: NetNS,
+    run_shell: bool,
+}
+impl GnomeSoftwareLauncher {
+
+    pub fn new(realm: Realm) -> Result<Self> {
+        let sandbox_status = SandboxStatus::load(SANDBOX_STATUS_FILE_DIRECTORY)?;
+        let status = sandbox_status.realm_status(&realm);
+        let netns = NetNS::new(NetNS::GS_NETNS_NAME);
+        Ok(GnomeSoftwareLauncher {
+            realm,
+            status,
+            netns,
+            run_shell: false,
+        })
+    }
+
+    pub fn set_run_shell(&mut self) {
+        self.run_shell = true;
+    }
+
+    fn ensure_flatpak_dir(&self) -> Result<()> {
+        let flatpak_user_dir = self.realm.base_path_file("flatpak");
+        if !flatpak_user_dir.exists() {
+            if let Err(err) = fs::create_dir(&flatpak_user_dir) {
+                bail!("failed to create realm flatpak directory ({}): {}", flatpak_user_dir.display(), err);
+            }
+            util::chown_user(&flatpak_user_dir)?;
+        }
+        Ok(())
+    }
+
+    fn add_flathub(&self) -> Result<()> {
+        let flatpak_user_dir = self.realm.base_path_file("flatpak");
+
+        match Command::new(FLATPAK_PATH)
+            .env("FLATPAK_USER_DIR", flatpak_user_dir)
+            .arg("remote-add")
+            .arg("--user")
+            .arg("--if-not-exists")
+            .arg("flathub")
+            .arg(FLATHUB_URL)
+            .status() {
+            Ok(status) => {
+                if status.success() {
+                    Ok(())
+
+                } else {
+                    bail!("failed to add flathub repo")
+                }
+            },
+            Err(err) =>  bail!("error running flatpak command: {}", err),
+        }
+    }
+
+    fn scan_tmp_directory(path: &Path) -> io::Result<Option<String>> {
+        for entry in fs::read_dir(&path)? {
+            let entry = entry?;
+            if entry.file_type()?.is_socket() {
+                if let Some(filename) = entry.path().file_name() {
+                    if let Some(filename) = filename.to_str() {
+                        if filename.starts_with("dbus-") {
+                            return Ok(Some(format!("/tmp/{}", filename)));
+                        }
+                    }
+                }
+            }
+        }
+        Ok(None)
+    }
+
+    fn find_dbus_socket(&self) -> Result<String> {
+        let pid = self.running_pid()?;
+        let tmp_dir = PathBuf::from(format!("/proc/{}/root/tmp", pid));
+        if !tmp_dir.is_dir() {
+            bail!("no /tmp directory found for process pid={}", pid);
+        }
+
+        if let Some(s) = Self::scan_tmp_directory(&tmp_dir)
+            .map_err(context!("error reading directory {}", tmp_dir.display()))? {
+            Ok(s)
+
+        } else {
+            bail!("no dbus socket found in /tmp directory for process pid={}", pid);
+        }
+    }
+
+    fn launch_sandbox(&self, status_file: &File) -> Result<()> {
+        self.ensure_flatpak_dir()?;
+        if let Err(err) = self.netns.nsenter() {
+            bail!("Failed to enter 'gnome-software' network namespace: {}", err);
+        }
+        verbose!("Entered network namespace ({})", NetNS::GS_NETNS_NAME);
+
+        if let Err(err) = util::drop_privileges(1000, 1000) {
+            bail!("Failed to drop privileges to uid = gid = 1000: {}", err);
+        }
+        verbose!("Dropped privileges (uid=1000, gid=1000)");
+
+        self.add_flathub()?;
+        let flatpak_user_dir = self.realm.base_path_file("flatpak");
+        let flatpak_user_dir = flatpak_user_dir.to_str().unwrap();
+
+        let cmd = if self.run_shell { "/usr/bin/bash" } else { "/usr/bin/gnome-software"};
+        verbose!("Running command in sandbox: {}", cmd);
+
+        BubbleWrap::new()
+            .ro_bind(&[
+                "/usr/bin",
+                "/usr/lib",
+                "/usr/libexec",
+                "/usr/share/dbus-1",
+                "/usr/share/icons",
+                "/usr/share/mime",
+                "/usr/share/X11",
+                "/usr/share/glib-2.0",
+                "/usr/share/xml",
+                "/usr/share/drirc.d",
+                "/usr/share/fontconfig",
+                "/usr/share/fonts",
+                "/usr/share/zoneinfo",
+                "/usr/share/swcatalog",
+
+                "/etc/passwd",
+                "/etc/machine-id",
+                "/etc/nsswitch.conf",
+                "/etc/fonts",
+                "/etc/ssl",
+                "/sys/dev/char", "/sys/devices",
+                "/run/user/1000/wayland-0",
+            ])
+            .ro_bind_to("/run/NetworkManager/resolv.conf", "/etc/resolv.conf")
+            .bind_to(flatpak_user_dir, "/home/citadel/realm-flatpak")
+            .create_symlinks(&[
+                ("usr/lib", "/lib64"),
+                ("usr/bin", "/bin"),
+                ("/tmp", "/var/tmp"),
+            ])
+            .create_dirs(&[
+                "/var/lib/flatpak",
+                "/home/citadel",
+                "/tmp",
+                "/sys/block", "/sys/bus", "/sys/class",
+            ])
+
+
+            .mount_dev()
+            .dev_bind("/dev/dri")
+            .mount_proc()
+            .unshare_all()
+            .share_net()
+
+            .clear_env()
+            .set_env_list(ENVIRONMENT)
+
+            .status_file(status_file)
+
+            .launch(&["dbus-run-session", "--", cmd])?;
+        Ok(())
+    }
+
+    pub fn new_realm_status_file(&self) -> Result<File> {
+        let path = Path::new(SANDBOX_STATUS_FILE_DIRECTORY).join(self.realm.name());
+        File::create(&path)
+            .map_err(context!("failed to open sandbox status file {}", path.display()))
+    }
+
+    pub fn launch(&self) -> Result<()> {
+        self.netns.ensure_exists()?;
+        if self.is_running() {
+            let cmd = if self.run_shell { "/usr/bin/bash" } else { "/usr/bin/gnome-software"};
+            self.launch_in_running_sandbox(&[cmd])?;
+        } else {
+            let status_file = self.new_realm_status_file()?;
+            self.ensure_flatpak_dir()?;
+            self.launch_sandbox(&status_file)?;
+        }
+        Ok(())
+    }
+
+    pub fn quit(&self) -> Result<()> {
+        if self.is_running() {
+            self.launch_in_running_sandbox(&["/usr/bin/gnome-software", "--quit"])?;
+        } else {
+            warn!("No running sandbox found for realm {}", self.realm.name());
+        }
+        Ok(())
+    }
+
+    pub fn is_running(&self) -> bool {
+        self.status.as_ref()
+            .map(|s| s.is_running())
+            .unwrap_or(false)
+    }
+
+    fn running_pid(&self) -> Result<u64> {
+        self.status.as_ref()
+            .map(|s| s.child_pid())
+            .ok_or(format_err!("no sandbox status available for realm '{}',", self.realm.name()))
+    }
+
+    fn dbus_session_address(&self) -> Result<String> {
+        let dbus_socket = Self::find_dbus_socket(&self)?;
+        Ok(format!("unix:path={}", dbus_socket))
+    }
+
+    fn launch_in_running_sandbox(&self, command: &[&str]) -> Result<()> {
+        let dbus_address = self.dbus_session_address()?;
+
+        let pid = self.running_pid()?.to_string();
+        let mut env = ENVIRONMENT.iter()
+            .map(|s| s.split_once('=').unwrap())
+            .collect::<Vec<_>>();
+        env.push(("DBUS_SESSION_BUS_ADDRESS", dbus_address.as_str()));
+
+        let err = Command::new("/usr/bin/nsenter")
+            .env_clear()
+            .envs( env )
+            .args(&[
+                "--all",
+                "--target", pid.as_str(),
+                "--setuid", "1000",
+                "--setgid", "1000",
+            ])
+            .args(command)
+            .exec();
+
+        Err(format_err!("failed to execute nsenter: {}", err))
+    }
+}

libcitadel/src/flatpak/mod.rs

@@ -0,0 +1,16 @@
+
+pub(crate) mod setup;
+pub(crate) mod status;
+
+pub(crate) mod bubblewrap;
+
+pub(crate) mod launcher;
+
+pub(crate) mod netns;
+
+pub use status::SandboxStatus;
+
+pub use bubblewrap::{BubbleWrap,BubbleWrapStatus,BubbleWrapRunningStatus,BubbleWrapExitStatus};
+pub use launcher::GnomeSoftwareLauncher;
+
+pub const SANDBOX_STATUS_FILE_DIRECTORY: &str = "/run/citadel/realms/gs-sandbox-status";

libcitadel/src/flatpak/netns.rs

@@ -0,0 +1,132 @@
+use std::ffi::OsStr;
+use std::path::Path;
+use std::process::Command;
+
+use crate::{util,Result};
+
+
+const BRIDGE_NAME: &str = "vz-clear";
+const VETH0: &str = "gs-veth0";
+const VETH1: &str = "gs-veth1";
+const IP_ADDRESS: &str = "172.17.0.222/24";
+const GW_ADDRESS: &str = "172.17.0.1";
+
+
+pub struct NetNS {
+    name: String,
+}
+
+impl NetNS {
+    pub const GS_NETNS_NAME: &'static str = "gnome-software";
+    pub fn new(name: &str) -> Self {
+        NetNS {
+            name: name.to_string(),
+        }
+    }
+
+    fn create(&self) -> crate::Result<()> {
+        Ip::new().link_add_veth(VETH0, VETH1).run()?;
+        Ip::new().link_set_netns(VETH0, &self.name).run()?;
+        Ip::new().link_set_master(VETH1, BRIDGE_NAME).run()?;
+        Ip::new().link_set_dev_up(VETH1).run()?;
+
+        Ip::new().ip_netns_exec_ip(&self.name).addr_add(IP_ADDRESS, VETH0).run()?;
+        Ip::new().ip_netns_exec_ip(&self.name).link_set_dev_up(VETH0).run()?;
+        Ip::new().ip_netns_exec_ip(&self.name).route_add_default(GW_ADDRESS).run()?;
+
+        Ok(())
+    }
+    pub fn ensure_exists(&self) -> Result<()> {
+        if Path::new(&format!("/run/netns/{}", self.name)).exists() {
+            verbose!("Network namespace ({}) exists", self.name);
+            return Ok(())
+        }
+        verbose!("Setting up network namespace ({})", self.name);
+
+        Ip::new().netns_add(&self.name).run()
+            .map_err(context!("Failed to add network namespace '{}'", self.name))?;
+
+        if let Err(err) = self.create() {
+            Ip::new().netns_delete(&self.name).run()?;
+            Err(err)
+        } else {
+            Ok(())
+        }
+    }
+
+    pub fn nsenter(&self) -> Result<()> {
+        util::nsenter_netns(&self.name)
+    }
+}
+const IP_PATH: &str = "/usr/sbin/ip";
+struct Ip {
+    command: Command,
+}
+
+impl Ip {
+
+    fn new() -> Self {
+        let mut command = Command::new(IP_PATH);
+        command.env_clear();
+        Ip { command }
+    }
+
+    fn add_args<S: AsRef<OsStr>>(&mut self, args: &[S]) -> &mut Self {
+        for arg in args {
+            self.command.arg(arg);
+        }
+        self
+    }
+
+    pub fn netns_add(&mut self, name: &str) -> &mut Self {
+        self.add_args(&["netns", "add", name])
+    }
+
+    pub fn netns_delete(&mut self, name: &str) -> &mut Self {
+        self.add_args(&["netns", "delete", name])
+    }
+
+    pub fn link_add_veth(&mut self, name: &str, peer_name: &str) -> &mut Self {
+        self.add_args(&["link", "add", name, "type", "veth", "peer", "name", peer_name])
+    }
+
+    pub fn link_set_netns(&mut self, iface: &str, netns_name: &str) -> &mut Self {
+        self.add_args(&["link", "set", iface, "netns", netns_name])
+    }
+
+    pub fn link_set_master(&mut self, iface: &str, bridge_name: &str) -> &mut Self {
+        self.add_args(&["link", "set", iface, "master", bridge_name])
+    }
+
+    pub fn link_set_dev_up(&mut self, iface: &str) -> &mut Self {
+        self.add_args(&["link", "set", "dev", iface, "up"])
+    }
+
+    pub fn ip_netns_exec_ip(&mut self, netns_name: &str) -> &mut Self {
+        self.add_args(&["netns", "exec", netns_name, IP_PATH])
+    }
+
+    pub fn addr_add(&mut self, ip_address: &str, dev: &str) -> &mut Self {
+        self.add_args(&["addr", "add", ip_address, "dev", dev])
+    }
+
+    pub fn route_add_default(&mut self, gateway: &str) -> &mut Self {
+        self.add_args(&["route", "add", "default", "via", gateway])
+    }
+
+    fn run(&mut self) -> crate::Result<()> {
+        verbose!("{:?}", self.command);
+        match self.command.status() {
+            Ok(status) => {
+                if status.success() {
+                    Ok(())
+                } else {
+                    bail!("IP command ({:?}) did not succeeed.", self.command);
+                }
+            }
+            Err(err) => {
+                bail!("error running ip command ({:?}): {}", self.command, err);
+            }
+        }
+    }
+}

libcitadel/src/flatpak/setup.rs

@@ -0,0 +1,58 @@
+use std::path::Path;
+use crate::{Realm, Result, util};
+
+const GNOME_SOFTWARE_DESKTOP_TEMPLATE: &str = "\
+[Desktop Entry]
+Name=Software
+Comment=Add, remove or update software on this computer
+Icon=org.gnome.Software
+Exec=/usr/libexec/launch-gnome-software --realm $REALM_NAME
+Terminal=false
+Type=Application
+Categories=GNOME;GTK;System;PackageManager;
+Keywords=Updates;Upgrade;Sources;Repositories;Preferences;Install;Uninstall;Program;Software;App;Store;
+StartupNotify=true
+";
+
+const APPLICATION_DIRECTORY: &str = "/home/citadel/.local/share/applications";
+
+pub struct FlatpakSetup<'a> {
+    realm: &'a Realm,
+}
+
+impl <'a> FlatpakSetup<'a> {
+
+    pub fn new(realm: &'a Realm) -> Self {
+        Self { realm }
+    }
+
+    pub fn setup(&self) -> Result<()> {
+        self.write_desktop_file()?;
+        self.ensure_flatpak_directory()?;
+        Ok(())
+    }
+
+
+    fn write_desktop_file(&self) -> Result<()> {
+        let appdir = Path::new(APPLICATION_DIRECTORY);
+        if !appdir.exists() {
+            util::create_dir(appdir)?;
+            if let Some(parent) = appdir.parent().and_then(|p| p.parent()) {
+                util::chown_tree(parent, (1000,1000), true)?;
+            }
+        }
+        let path = appdir.join(format!("realm-{}.org.gnome.Software.desktop", self.realm.name()));
+        util::write_file(path, GNOME_SOFTWARE_DESKTOP_TEMPLATE.replace("$REALM_NAME", self.realm.name()))?;
+        Ok(())
+    }
+
+    fn ensure_flatpak_directory(&self) -> Result<()> {
+        let path = self.realm.base_path_file("flatpak");
+        if !path.exists() {
+            util::create_dir(&path)?;
+            util::chown_user(&path)?;
+        }
+        Ok(())
+    }
+
+}

libcitadel/src/flatpak/status.rs

@@ -0,0 +1,144 @@
+use std::collections::HashMap;
+use std::fs::File;
+use std::path::{Path, PathBuf};
+use std::time::SystemTime;
+use crate::flatpak::bubblewrap::BubbleWrapStatus;
+use crate::{Realm, Result, util};
+
+
+/// Utility function to read modified time from a path.
+fn modified_time(path: &Path) -> Result<SystemTime> {
+    path.metadata().and_then(|meta| meta.modified())
+        .map_err(context!("failed to read modified time from '{}'", path.display()))
+}
+
+/// Utility function to detect if current modified time of a path
+/// matches an earlier recorded modified time.
+fn modified_changed(path: &Path, old_modified: SystemTime) -> bool {
+    if !path.exists() {
+        // Path existed at some earlier point, so something changed
+        return true;
+    }
+
+    match modified_time(path) {
+        Ok(modified) => old_modified != modified,
+        Err(err) => {
+            // Print a warning but assume change
+            warn!("{}", err);
+            true
+        },
+    }
+}
+
+/// Records the content of single entry in a sandbox status directory.
+///
+/// The path to the status file as well as the last modified time are
+/// recorded so that changes in status of a sandbox can be detected.
+struct StatusEntry {
+    status: BubbleWrapStatus,
+    path: PathBuf,
+    modified: SystemTime,
+}
+
+
+impl StatusEntry {
+
+    fn load_timestamp_and_status(path: &Path) -> Result<Option<(SystemTime, BubbleWrapStatus)>> {
+        if path.exists() {
+            let modified = modified_time(path)?;
+            if let Some(status) = BubbleWrapStatus::parse_file(path)? {
+                return Ok(Some((modified, status)));
+            }
+        }
+        Ok(None)
+    }
+
+    fn load(base_dir: &Path, name: &str) -> Result<Option<Self>> {
+        let path = base_dir.join(name);
+        let result = StatusEntry::load_timestamp_and_status(&path)?
+            .map(|(modified, status)| StatusEntry { status, path, modified });
+        Ok(result)
+    }
+
+    fn is_modified(&self) -> bool {
+        modified_changed(&self.path, self.modified)
+    }
+}
+
+
+/// Holds information about entries in a sandbox status directory.
+///
+/// Bubblewrap accepts a command line argument that asks for status
+/// information to be written as a json structure to a file descriptor.
+///
+pub struct SandboxStatus {
+    base_dir: PathBuf,
+    base_modified: SystemTime,
+    entries: HashMap<String, StatusEntry>,
+}
+
+impl SandboxStatus {
+
+    pub fn need_reload(&self) -> bool {
+        if modified_changed(&self.base_dir, self.base_modified) {
+            return true;
+        }
+        self.entries.values().any(|entry| entry.is_modified())
+    }
+
+    fn process_dir_entry(&mut self, dir_entry: PathBuf) -> Result<()> {
+        fn realm_name_for_path(path: &Path) -> Option<&str> {
+            path.file_name()
+                .and_then(|name| name.to_str())
+                .filter(|name| Realm::is_valid_name(name))
+
+        }
+        if dir_entry.is_file() {
+            if let Some(name) = realm_name_for_path(&dir_entry) {
+                if let Some(entry) = StatusEntry::load(&self.base_dir, name)? {
+                    self.entries.insert(name.to_string(), entry);
+                }
+            }
+        }
+        Ok(())
+    }
+
+    pub fn reload(&mut self) -> Result<()> {
+        self.entries.clear();
+        self.base_modified = modified_time(&self.base_dir)?;
+        let base_dir = self.base_dir.clone();
+        util::read_directory(&base_dir, |entry| {
+            self.process_dir_entry(entry.path())
+        })
+    }
+
+    fn new(base_dir: &Path) -> Result<Self> {
+        let base_dir = base_dir.to_owned();
+        let base_modified = modified_time(&base_dir)?;
+        Ok(SandboxStatus {
+            base_dir,
+            base_modified,
+            entries: HashMap::new(),
+        })
+    }
+
+    pub fn load(directory: impl AsRef<Path>) -> Result<SandboxStatus> {
+        let base_dir = directory.as_ref();
+        if !base_dir.exists() {
+            util::create_dir(base_dir)?;
+        }
+        let mut status = SandboxStatus::new(base_dir)?;
+        status.reload()?;
+        Ok(status)
+    }
+
+    pub fn realm_status(&self, realm: &Realm) -> Option<BubbleWrapStatus> {
+        self.entries.get(realm.name()).map(|entry| entry.status.clone())
+    }
+
+    pub fn new_realm_status_file(&self, realm: &Realm) -> Result<File> {
+        let path = self.base_dir.join(realm.name());
+        File::create(&path)
+            .map_err(context!("failed to open sandbox status file {}", path.display()))
+    }
+}

libcitadel/src/lib.rs

@@ -21,6 +21,8 @@ mod realm;
 pub mod terminal;
 mod system;
 
+pub mod flatpak;
+
 pub use crate::config::OsRelease;
 pub use crate::blockdev::BlockDev;
 pub use crate::cmdline::CommandLine;

libcitadel/src/log.rs

@@ -62,6 +62,11 @@ impl Logger {
         logger.level = level;
     }
 
+    pub fn is_log_level(level: LogLevel) -> bool {
+        let logger = LOGGER.lock().unwrap();
+        logger.level >= level
+    }
+
     pub fn set_log_output(output: Box<dyn LogOutput>) {
         let mut logger = LOGGER.lock().unwrap();
         logger.output = output;

libcitadel/src/realm/config.rs

@@ -77,6 +77,9 @@ pub struct RealmConfig {
     #[serde(rename="use-fuse")]
     pub use_fuse: Option<bool>,
 
+    #[serde(rename="use-flatpak")]
+    pub use_flatpak: Option<bool>,
+
     #[serde(rename="use-gpu")]
     pub use_gpu: Option<bool>,
 
@@ -201,6 +204,7 @@ impl RealmConfig {
             wayland_socket: Some("wayland-0".to_string()),
             use_kvm: Some(false),
             use_fuse: Some(false),
+            use_flatpak: Some(false),
             use_gpu: Some(false),
             use_gpu_card0: Some(false),
             use_network: Some(true),
@@ -233,6 +237,7 @@ impl RealmConfig {
             wayland_socket: None,
             use_kvm: None,
             use_fuse: None,
+            use_flatpak: None,
             use_gpu: None,
             use_gpu_card0: None,
             use_network: None,
@@ -267,6 +272,14 @@ impl RealmConfig {
         self.bool_value(|c| c.use_fuse)
     }
 
+    /// If `true` flatpak directory will be mounted into realm
+    /// and a desktop file will be created to launch gnome-software
+    ///
+    pub fn flatpak(&self) -> bool {
+        self.bool_value(|c| c.use_flatpak)
+    }
+
+
     /// If `true` render node device /dev/dri/renderD128 will be added to realm.
     ///
     /// This enables hardware graphics acceleration in realm.

libcitadel/src/realm/launcher.rs

@@ -60,7 +60,7 @@ impl <'a> RealmLauncher <'a> {
         if config.kvm() {
             self.add_device("/dev/kvm");
         }
-        if config.fuse() {
+        if config.fuse() || config.flatpak() {
             self.add_device("/dev/fuse");
         }
 
@@ -153,6 +153,10 @@ impl <'a> RealmLauncher <'a> {
             writeln!(s, "BindReadOnly=/run/user/1000/{}:/run/user/host/wayland-0", config.wayland_socket())?;
         }
 
+        if config.flatpak() {
+            writeln!(s, "BindReadOnly={}:/var/lib/flatpak", self.realm.base_path_file("flatpak").display())?;
+        }
+
         for bind in config.extra_bindmounts() {
             if Self::is_valid_bind_item(bind) {
                 writeln!(s, "Bind={}", bind)?;

libcitadel/src/realm/manager.rs

@@ -4,6 +4,8 @@ use std::sync::{Arc, RwLock, RwLockReadGuard, RwLockWriteGuard};
 use posix_acl::{ACL_EXECUTE, ACL_READ, PosixACL, Qualifier};
 
 use crate::{Mountpoint, Result, Realms, RealmFS, Realm, util};
+use crate::flatpak::GnomeSoftwareLauncher;
+use crate::flatpak::setup::FlatpakSetup;
 use crate::realm::pidmapper::{PidLookupResult, PidMapper};
 use crate::realmfs::realmfs_set::RealmFSSet;
 
@@ -21,6 +23,7 @@ struct Inner {
     events: RealmEventListener,
     realms: Realms,
     realmfs_set: RealmFSSet,
+    pid_mapper: PidMapper,
 }
 
 impl Inner {
@@ -28,7 +31,8 @@ impl Inner {
         let events = RealmEventListener::new();
         let realms = Realms::load()?;
         let realmfs_set = RealmFSSet::load()?;
-        Ok(Inner { events, realms, realmfs_set })
+        let pid_mapper = PidMapper::new()?;
+        Ok(Inner { events, realms, realmfs_set, pid_mapper })
     }
 }
 
@@ -230,6 +234,10 @@ impl RealmManager {
             self.ensure_run_media_directory()?;
         }
 
+        if realm.config().flatpak() {
+            FlatpakSetup::new(realm).setup()?;
+        }
+
         self.systemd.start_realm(realm, &rootfs)?;
 
         self.create_realm_namefile(realm)?;
@@ -268,6 +276,15 @@ impl RealmManager {
         self.run_in_realm(realm, &["/usr/bin/ln", "-s", "/run/user/host/wayland-0", "/run/user/1000/wayland-0"], false)
     }
 
+    fn stop_gnome_software_sandbox(&self, realm: &Realm) -> Result<()> {
+        let launcher = GnomeSoftwareLauncher::new(realm.clone())?;
+        if launcher.is_running() {
+            info!("Stopping GNOME Software sandbox for {}", realm.name());
+            launcher.quit()?;
+        }
+        Ok(())
+    }
+
     pub fn stop_realm(&self, realm: &Realm) -> Result<()> {
         if !realm.is_active() {
             info!("ignoring stop request on realm '{}' which is not running", realm.name());
@@ -276,6 +293,12 @@ impl RealmManager {
 
         info!("Stopping realm {}", realm.name());
 
+        if realm.config().flatpak() {
+            if let Err(err) = self.stop_gnome_software_sandbox(realm) {
+                warn!("Error stopping GNOME Software sandbox: {}", err);
+            }
+        }
+
         realm.set_active(false);
         self.systemd.stop_realm(realm)?;
         realm.cleanup_rootfs();
@@ -335,8 +358,8 @@ impl RealmManager {
     }
 
     pub fn realm_by_pid(&self, pid: u32) -> PidLookupResult {
-        let mapper = PidMapper::new(self.active_realms(false));
-        mapper.lookup_pid(pid as libc::pid_t)
+        let realms = self.realm_list();
+        self.inner_mut().pid_mapper.lookup_pid(pid as libc::pid_t, realms)
     }
 
     pub fn rescan_realms(&self) -> Result<(Vec<Realm>,Vec<Realm>)> {

libcitadel/src/realm/pidmapper.rs

@@ -1,6 +1,7 @@
 use std::ffi::OsStr;
 use procfs::process::Process;
-use crate::Realm;
+use crate::{Result, Realm};
+use crate::flatpak::{SANDBOX_STATUS_FILE_DIRECTORY, SandboxStatus};
 
 pub enum PidLookupResult {
     Unknown,
@@ -9,14 +10,15 @@ pub enum PidLookupResult {
 }
 
 pub struct PidMapper {
-    active_realms: Vec<Realm>,
+    sandbox_status: SandboxStatus,
     my_pid_ns_id: Option<u64>,
 }
 
 impl PidMapper {
-    pub fn new(active_realms: Vec<Realm>) -> Self {
+    pub fn new() -> Result<Self> {
+        let sandbox_status = SandboxStatus::load(SANDBOX_STATUS_FILE_DIRECTORY)?;
         let my_pid_ns_id = Self::self_pid_namespace_id();
-        PidMapper { active_realms, my_pid_ns_id }
+        Ok(PidMapper { sandbox_status, my_pid_ns_id })
     }
 
     fn read_process(pid: libc::pid_t) -> Option<Process> {
@@ -72,7 +74,30 @@ impl PidMapper {
         Self::read_process(ppid)
     }
 
-    pub fn lookup_pid(&self, pid: libc::pid_t) -> PidLookupResult {
+    fn refresh_sandbox_status(&mut self) -> Result<()> {
+        if self.sandbox_status.need_reload() {
+            self.sandbox_status.reload()?;
+        }
+        Ok(())
+    }
+
+    fn search_sandbox_realms(&mut self, pid_ns: u64, realms: &[Realm]) -> Option<Realm> {
+        if let Err(err) = self.refresh_sandbox_status() {
+            warn!("error reloading sandbox status directory: {}", err);
+            return None;
+        }
+
+        for r in realms {
+            if let Some(status) = self.sandbox_status.realm_status(r) {
+                if status.pid_namespace() == pid_ns {
+                    return Some(r.clone())
+                }
+            }
+        }
+        None
+    }
+
+    pub fn lookup_pid(&mut self, pid: libc::pid_t, realms: Vec<Realm>) -> PidLookupResult {
         const MAX_PARENT_SEARCH: i32 = 8;
         let mut n = 0;
 
@@ -92,13 +117,17 @@ impl PidMapper {
                 return PidLookupResult::Citadel;
             }
 
-            if let Some(realm) = self.active_realms.iter()
-                .find(|r| r.has_pid_ns(pid_ns_id))
+            if let Some(realm) = realms.iter()
+                .find(|r| r.is_active() && r.has_pid_ns(pid_ns_id))
                 .cloned()
             {
                 return PidLookupResult::Realm(realm)
             }
 
+            if let Some(r) = self.search_sandbox_realms(pid_ns_id, &realms) {
+                return PidLookupResult::Realm(r)
+            }
+
             proc = match Self::parent_process(proc) {
                 Some(proc) => proc,
                 None => return PidLookupResult::Unknown,
@@ -108,5 +137,4 @@ impl PidMapper {
         }
         PidLookupResult::Unknown
     }
-
 }

libcitadel/src/realm/realm.rs

@@ -279,6 +279,9 @@ impl Realm {
         symlink::write(&rootfs, self.rootfs_symlink(), false)?;
         symlink::write(mountpoint.path(), self.realmfs_mountpoint_symlink(), false)?;
         symlink::write(self.base_path().join("home"), self.run_path().join("home"), false)?;
+        if self.config().flatpak() {
+            symlink::write(self.base_path().join("flatpak"), self.run_path().join("flatpak"), false)?;
+        }
 
         Ok(rootfs)
     }
@@ -300,6 +303,9 @@ impl Realm {
         Self::remove_symlink(self.realmfs_mountpoint_symlink());
         Self::remove_symlink(self.rootfs_symlink());
         Self::remove_symlink(self.run_path().join("home"));
+        if self.config().flatpak() {
+            Self::remove_symlink(self.run_path().join("flatpak"));
+        }
 
         if let Err(e) = fs::remove_dir(self.run_path()) {
             warn!("failed to remove run directory {}: {}", self.run_path().display(), e);

libcitadel/src/realm/systemd.rs

@@ -31,6 +31,28 @@ impl Systemd {
         if realm.config().ephemeral_home() {
             self.setup_ephemeral_home(realm)?;
         }
+        if realm.config().flatpak() {
+            self.setup_flatpak_workaround(realm)?;
+        }
+        Ok(())
+    }
+
+    // What even is this??
+    //
+    // Good question.
+    //
+    // https://bugzilla.redhat.com/show_bug.cgi?id=2210335#c10
+    //
+    fn setup_flatpak_workaround(&self, realm: &Realm) -> Result<()> {
+        let commands = &[
+            vec!["/usr/bin/mount", "-m", "-t","proc", "proc", "/run/flatpak-workaround/proc"],
+            vec!["/usr/bin/chmod", "700", "/run/flatpak-workaround"],
+        ];
+
+        for cmd in commands {
+            Self::machinectl_shell(realm, cmd, "root", false, true)?;
+        }
+
         Ok(())
     }
 

libcitadel/src/util.rs

@@ -7,6 +7,7 @@ use std::env;
 use std::fs::{self, File, DirEntry};
 use std::ffi::CString;
 use std::io::{self, Seek, Read, BufReader, SeekFrom};
+use std::os::fd::AsRawFd;
 use std::time::{SystemTime, UNIX_EPOCH};
 
 use walkdir::WalkDir;
@@ -217,7 +218,8 @@ where
 ///
 pub fn remove_file(path: impl AsRef<Path>) -> Result<()> {
     let path = path.as_ref();
-    if path.exists() {
+    let is_symlink = fs::symlink_metadata(path).is_ok();
+    if is_symlink || path.exists() {
         fs::remove_file(path)
             .map_err(context!("failed to remove file {:?}", path))?;
     }
@@ -368,9 +370,38 @@ pub fn touch_mtime(path: &Path) -> Result<()> {
 
     utimes(path, meta.atime(),mtime)?;
     Ok(())
-
-
-
-
-
+}
+
+pub fn nsenter_netns(netns: &str) -> Result<()> {
+    let mut path = PathBuf::from("/run/netns");
+    path.push(netns);
+    if !path.exists() {
+        bail!("Network namespace '{}' does not exist", netns);
+    }
+    let f = File::open(&path)
+        .map_err(context!("error opening netns file {}", path.display()))?;
+
+    let fd = f.as_raw_fd();
+
+    unsafe {
+        if libc::setns(fd, libc::CLONE_NEWNET) == -1 {
+            let err = io::Error::last_os_error();
+            bail!("failed to setns() into network namespace '{}': {}", netns, err);
+        }
+    }
+    Ok(())
+}
+
+pub fn drop_privileges(uid: u32, gid: u32) -> Result<()> {
+    unsafe {
+        if libc::setgid(gid) == -1 {
+            let err = io::Error::last_os_error();
+            bail!("failed to call setgid({}): {}", gid, err);
+
+        } else if libc::setuid(uid) == -1 {
+            let err = io::Error::last_os_error();
+            bail!("failed to call setuid({}): {}", uid, err);
+        }
+    }
+    Ok(())
 }

systemd/citadel-desktop-watcher.path

@@ -4,6 +4,6 @@ StartLimitIntervalSec=0
 
 [Path]
 PathChanged=/run/citadel/realms/current/current.realm/rootfs/usr/share/applications
-PathChanged=/run/citadel/realms/current/current.realm/rootfs/var/lib/flatpak/exports/share/applications
+PathChanged=/run/citadel/realms/current/current.realm/flatpak/exports/share/applications
 PathChanged=/run/citadel/realms/current/current.realm/home/.local/share/applications
 PathChanged=/run/citadel/realms/current/current.realm/home/.local/share/flatpak/exports/share/applications