codecraft/server/src/sandbox.rs

//! Per-user sandbox for shell commands (and git) using bubblewrap.
//!
//! A sandboxed command sees the system read-only, only the user's folders
//! writable, its own home directory, a private /tmp, its own process
//! namespace and an empty environment (no server secrets). The network is
//! shared so package managers keep working.

use crate::app::App;
use std::path::{Path, PathBuf};
use std::sync::OnceLock;
use tokio::process::Command;

/// What a sandboxed process may access.
#[derive(Debug, Clone)]
pub struct SandboxSpec {
    pub username: String,
    /// Writable directories (the user's roots).
    pub roots: Vec<PathBuf>,
    /// Host directory mounted as the user's home.
    pub home: PathBuf,
    /// Extra environment (the user's git identity).
    pub env: Vec<(String, String)>,
}

impl SandboxSpec {
    pub fn home_inside(&self) -> String {
        format!("/home/{}", self.username)
    }
}

static AVAILABLE: OnceLock<Result<(), String>> = OnceLock::new();

/// Check once whether bubblewrap works in this environment.
pub async fn probe() -> Result<(), String> {
    if let Some(r) = AVAILABLE.get() {
        return r.clone();
    }
    let res = match Command::new("bwrap")
        .args(["--ro-bind", "/usr", "/usr", "--ro-bind", "/bin", "/bin", "--ro-bind", "/lib", "/lib", "--dev", "/dev", "--proc", "/proc"])
        .args(["--unshare-all", "--die-with-parent", "--clearenv", "/bin/true"])
        .env_clear()
        .output()
        .await
    {
        Ok(o) if o.status.success() => Ok(()),
        Ok(o) => Err(String::from_utf8_lossy(&o.stderr).trim().to_string()),
        Err(e) => Err(format!("bubblewrap is not installed: {e}")),
    };
    match &res {
        Ok(()) => tracing::info!("sandbox: bubblewrap available"),
        Err(e) => tracing::warn!("sandbox: bubblewrap unavailable – shell commands of non-admin users are disabled ({e})"),
    }
    let _ = AVAILABLE.set(res.clone());
    res
}

pub fn available() -> bool {
    matches!(AVAILABLE.get(), Some(Ok(())))
}

/// The sandbox for a session owner, or None if commands run unsandboxed
/// (admins in "auto" mode, or sandbox mode "off").
pub fn spec_for(app: &App, owner_id: Option<&str>) -> Option<SandboxSpec> {
    let mode = app.config().sandbox.mode.clone();
    if mode == "off" {
        return None;
    }
    let user = owner_id.and_then(|id| app.store.user(id).ok().flatten())?;
    if user.is_admin() && mode != "always" {
        return None;
    }
    let home = app.data_dir().join("users").join(&user.username).join("home");
    let _ = std::fs::create_dir_all(&home);
    Some(SandboxSpec { username: user.username.clone(), roots: app.user_roots(Some(&user.id)), home, env: crate::gitcreds::identity_env(app, &user.id) })
}

/// Build a command that runs `program args` inside the sandbox in `cwd`.
pub fn command(spec: &SandboxSpec, cwd: &Path, program: &str, args: &[&str]) -> Command {
    command_with(spec, cwd, &[], program, args)
}

/// Like `command`, with extra host directories mounted read-only (e.g. tools).
pub fn command_with(spec: &SandboxSpec, cwd: &Path, extra_ro: &[&Path], program: &str, args: &[&str]) -> Command {
    let mut c = Command::new("bwrap");
    // Empty environment: bubblewrap's own helper process must not carry secrets.
    c.env_clear();
    c.args(bwrap_args(spec, cwd, extra_ro, true, program, args));
    c
}

/// Arguments for `bwrap` running `program args` in the sandbox. `new_session`
/// detaches from the controlling terminal (protects the caller's tty); a
/// terminal with its own PTY leaves it off to keep job control.
pub fn bwrap_args(spec: &SandboxSpec, cwd: &Path, extra_ro: &[&Path], new_session: bool, program: &str, args: &[&str]) -> Vec<std::ffi::OsString> {
    let mut c: Vec<std::ffi::OsString> = Vec::new();
    let mut push = |items: &[&dyn AsRef<std::ffi::OsStr>]| {
        for i in items {
            c.push(i.as_ref().to_os_string());
        }
    };
    for dir in ["/usr", "/bin", "/lib", "/etc", "/sbin", "/opt"] {
        if Path::new(dir).is_dir() && !Path::new(dir).is_symlink() {
            push(&[&"--ro-bind", &dir, &dir]);
        } else if let Ok(target) = std::fs::read_link(dir) {
            push(&[&"--symlink", &target, &dir]);
        }
    }
    for dir in ["/lib64", "/lib32"] {
        let p = Path::new(dir);
        if let Ok(target) = std::fs::read_link(p) {
            push(&[&"--symlink", &target, &dir]);
        } else if p.is_dir() {
            push(&[&"--ro-bind", &dir, &dir]);
        }
    }
    for root in &spec.roots {
        push(&[&"--bind", root, root]);
    }
    // Built-in skills and templates are readable (not writable) in the sandbox.
    let builtin = crate::prompts::builtin_resources();
    for dir in extra_ro.iter().copied().chain(std::iter::once(builtin.as_path())) {
        if dir.exists() {
            push(&[&"--ro-bind", &dir, &dir]);
        }
    }
    let home = spec.home_inside();
    push(&[&"--bind", &spec.home, &home]);
    push(&[&"--tmpfs", &"/tmp", &"--dev", &"/dev", &"--proc", &"/proc"]);
    push(&[&"--unshare-all", &"--share-net", &"--die-with-parent", &"--clearenv"]);
    if new_session {
        push(&[&"--new-session"]);
    }
    let path = format!("{home}/.local/bin:{home}/.cargo/bin:{home}/.npm-global/bin:/usr/local/bin:/usr/bin:/bin");
    let npm = format!("{home}/.npm-global");
    let pipx = format!("{home}/.local/pipx");
    let pipx_bin = format!("{home}/.local/bin");
    for (k, v) in [
        ("HOME", home.as_str()),
        ("USER", spec.username.as_str()),
        ("PATH", path.as_str()),
        ("LANG", "C.UTF-8"),
        ("TERM", "xterm-256color"),
        ("CODECRAFT", "1"),
        ("GIT_TERMINAL_PROMPT", "0"),
        ("PAGER", "cat"),
        ("PIP_BREAK_SYSTEM_PACKAGES", "1"),
        ("NPM_CONFIG_PREFIX", npm.as_str()),
        ("PIPX_HOME", pipx.as_str()),
        ("PIPX_BIN_DIR", pipx_bin.as_str()),
    ] {
        push(&[&"--setenv", &k, &v]);
    }
    for (k, v) in &spec.env {
        push(&[&"--setenv", k, v]);
    }
    push(&[&"--chdir", &cwd, &program]);
    for a in args {
        push(&[a]);
    }
    c
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn git_identity_reaches_the_sandbox() {
        let spec = SandboxSpec {
            username: "ann".into(),
            roots: vec![],
            home: PathBuf::from("/tmp/ann"),
            env: vec![("GIT_AUTHOR_NAME".into(), "Ann Example".into())],
        };
        let args: Vec<String> = bwrap_args(&spec, Path::new("/tmp"), &[], true, "bash", &[]).into_iter().map(|a| a.to_string_lossy().into_owned()).collect();
        let i = args.iter().position(|a| a == "GIT_AUTHOR_NAME").expect("identity set");
        assert_eq!(args[i - 1], "--setenv");
        assert_eq!(args[i + 1], "Ann Example");
    }
}