zeph_tools/sandbox/

mod.rs

// SPDX-FileCopyrightText: 2026 Andrei G <bug-ops>
// SPDX-License-Identifier: MIT OR Apache-2.0

//! OS-level sandbox abstractions for subprocess tool execution.
//!
//! This module provides a portable [`Sandbox`] trait and platform-specific backends that
//! restrict filesystem, network, and syscall access for shell commands spawned by
//! `ShellExecutor`.
//!
//! # Scope (NFR-SB-1)
//!
//! The sandbox applies **only to subprocess executors** (`ShellExecutor`). In-process executors
//! (`WebScrapeExecutor`, `FileExecutor`) do not spawn a child process and are therefore not
//! subject to OS-level sandboxing. Application-layer controls (allowed hosts, path allowlists)
//! govern those executors instead.
//!
//! # Platform support
//!
//! | Platform | Backend | Compiled |
//! |----------|---------|----------|
//! | macOS | `sandbox-exec` (Seatbelt) | always |
//! | Linux + `sandbox` feature | `bwrap` + Landlock + seccomp | `#[cfg(all(target_os="linux", feature="sandbox"))]` |
//! | Other | `NoopSandbox` (logs WARN) | always |
//!
//! # Example
//!
//! ```rust,no_run
//! use zeph_tools::{build_sandbox, SandboxPolicy, SandboxProfile};
//! use tokio::process::Command;
//!
//! # fn example() -> Result<(), Box<dyn std::error::Error>> {
//! let policy = SandboxPolicy {
//!     profile: SandboxProfile::Workspace,
//!     allow_read: vec![],
//!     allow_write: vec![std::env::current_dir()?],
//!     allow_network: false,
//!     allow_exec: vec![],
//!     env_inherit: vec![],
//!     denied_domains: vec![],
//! };
//! let sb = build_sandbox(false)?;
//! let mut cmd = Command::new("bash");
//! cmd.arg("-c").arg("echo hello");
//! sb.wrap(&mut cmd, &policy)?;
//! # Ok(())
//! # }
//! ```

use std::path::PathBuf;

use thiserror::Error;

pub mod noop;

#[cfg(target_os = "macos")]
pub mod macos;

#[cfg(all(target_os = "linux", feature = "sandbox"))]
pub mod linux;

pub use noop::NoopSandbox;

#[cfg(target_os = "macos")]
pub use macos::MacosSandbox;

#[cfg(all(target_os = "linux", feature = "sandbox"))]
pub use linux::LinuxSandbox;

/// Declarative sandbox policy evaluated at command launch.
///
/// Applied *after* blocklist, `PolicyGate`, and `TrustGate` have accepted the call.
/// The sandbox is the last hard boundary, not a replacement for application-level controls.
#[derive(Debug, Clone)]
pub struct SandboxPolicy {
    /// The enforcement profile controlling which restrictions are active.
    pub profile: SandboxProfile,
    /// Paths granted read (and execute) access. Normalized to absolute paths at construction.
    ///
    /// Paths are resolved to their canonical (real) form by [`SandboxPolicy::canonicalized`]
    /// before being applied. If a path is a symlink, the resolved target is used for the allow
    /// rule. Deny rules for well-known secret paths are also generated for the canonical form,
    /// so the allow override works correctly even when the denied path is a symlink.
    pub allow_read: Vec<PathBuf>,
    /// Paths granted read and write access. Normalized to absolute paths at construction.
    pub allow_write: Vec<PathBuf>,
    /// Whether unrestricted network egress is permitted.
    pub allow_network: bool,
    /// Additional executables or directories granted execute permission.
    pub allow_exec: Vec<PathBuf>,
    /// Environment variable names or prefixes that are inherited by the sandboxed child.
    pub env_inherit: Vec<String>,
    /// Hostname patterns (exact or `*.suffix`) denied network egress.
    ///
    /// Enforcement is per-backend:
    /// - macOS Seatbelt: `(deny network* (remote host "<host>"))` after `(allow network*)`.
    /// - Linux bwrap: `/etc/hosts` override resolving the name to `0.0.0.0` (best-effort).
    /// - [`NoopSandbox`]: ignored (log WARN at construction if non-empty).
    pub denied_domains: Vec<String>,
}

impl SandboxPolicy {
    /// Canonicalize all path fields so that symlinks and `..` components cannot bypass
    /// the policy. Paths that cannot be resolved (e.g., non-existent) are dropped and
    /// logged at WARN level with the OS error — callers should ensure paths exist
    /// before adding them to the policy.
    #[must_use]
    pub fn canonicalized(mut self) -> Self {
        self.allow_read = canonicalize_paths(self.allow_read);
        self.allow_write = canonicalize_paths(self.allow_write);
        self.allow_exec = canonicalize_paths(self.allow_exec);
        self
    }
}

fn canonicalize_paths(paths: Vec<PathBuf>) -> Vec<PathBuf> {
    paths
        .into_iter()
        .filter_map(|p| match std::fs::canonicalize(&p) {
            Ok(canonical) => {
                if canonical != p {
                    tracing::debug!(
                        "sandbox: resolved symlink {} → {}",
                        p.display(),
                        canonical.display()
                    );
                }
                Some(canonical)
            }
            Err(e) => {
                tracing::warn!(
                    path = %p.display(),
                    error = %e,
                    "sandbox: allow-list path could not be canonicalized and was dropped from policy"
                );
                None
            }
        })
        .collect()
}

impl Default for SandboxPolicy {
    fn default() -> Self {
        let cwd =
            std::fs::canonicalize(std::env::current_dir().unwrap_or_else(|_| PathBuf::from(".")))
                .unwrap_or_else(|_| PathBuf::from("/"));
        Self {
            profile: SandboxProfile::Workspace,
            allow_read: vec![cwd.clone()],
            allow_write: vec![cwd],
            allow_network: false,
            allow_exec: vec![],
            env_inherit: vec![],
            denied_domains: vec![],
        }
    }
}

pub(crate) use zeph_config::tools::SandboxProfile;

#[non_exhaustive]
/// Error returned when sandbox setup or policy application fails.
#[derive(Debug, Error)]
pub enum SandboxError {
    /// The OS backend binary or kernel API is unavailable on this system.
    #[error("sandbox backend unavailable: {reason}")]
    Unavailable { reason: String },
    /// The configured policy is not supported by the backend.
    #[error("policy not supported by {backend}: {reason}")]
    UnsupportedPolicy {
        /// Backend name for diagnostics.
        backend: &'static str,
        /// Human-readable explanation.
        reason: String,
    },
    /// I/O error during sandbox setup (e.g. temp file creation).
    #[error("sandbox setup failed: {0}")]
    Setup(#[from] std::io::Error),
    /// Policy string generation failed.
    #[error("policy generation failed: {0}")]
    Policy(String),
}

/// Operating-system sandbox backend.
///
/// `wrap` is the sole entry point. Implementations rewrite a [`tokio::process::Command`]
/// in place so that the next `.spawn()` launches inside the OS sandbox. Implementations
/// must be fork-safe: state installed via the command builder must survive `fork()+exec()`.
///
/// # Contract for implementors
///
/// - Must not spawn the child themselves — only rewrite `cmd`.
/// - Must not use `unsafe` code.
/// - When the profile is [`SandboxProfile::Off`], `wrap` MUST be a no-op.
pub trait Sandbox: Send + Sync + std::fmt::Debug {
    /// Short identifier for logging and diagnostics (e.g., `"macos-seatbelt"`, `"linux-bwrap"`).
    fn name(&self) -> &'static str;

    /// Verify that `policy` is expressible on this backend.
    ///
    /// # Errors
    ///
    /// Returns [`SandboxError::UnsupportedPolicy`] when a required feature is missing.
    fn supports(&self, policy: &SandboxPolicy) -> Result<(), SandboxError>;

    /// Rewrite `cmd` to execute inside the OS sandbox described by `policy`.
    ///
    /// Called synchronously in the executor thread. Must not block on I/O for more than a few
    /// milliseconds (temp file writes are acceptable; network calls are not).
    ///
    /// # Errors
    ///
    /// Returns [`SandboxError`] if wrapping fails (binary missing, profile generation error, etc.).
    fn wrap(
        &self,
        cmd: &mut tokio::process::Command,
        policy: &SandboxPolicy,
    ) -> Result<(), SandboxError>;
}

/// Construct the best available [`Sandbox`] backend for the current platform.
///
/// Selection order:
/// 1. macOS → `MacosSandbox`
/// 2. Linux + `sandbox` feature → `LinuxSandbox`
/// 3. Fallback → [`NoopSandbox`]
///
/// # Errors
///
/// Returns [`SandboxError::Unavailable`] when `strict = true` and the preferred backend
/// is missing (e.g. `bwrap` not on `PATH`).
pub fn build_sandbox(strict: bool) -> Result<Box<dyn Sandbox>, SandboxError> {
    build_sandbox_with_policy(strict, false, false)
}

/// Construct the best available [`Sandbox`] backend with additional safety options.
///
/// Extends [`build_sandbox`] with:
/// - `fail_if_unavailable`: when `true`, even a successful noop fallback is an error.
///   Use this when `denied_domains` must be enforced and no effective sandbox exists.
/// - `denied_domains_present`: when `true` and the noop backend is selected with
///   `fail_if_unavailable = false`, emits a one-shot `WARN` that the deny list is unenforceable.
///
/// # Errors
///
/// - [`SandboxError::Unavailable`] when `strict = true` and the preferred backend binary is
///   missing (same as [`build_sandbox`]).
/// - [`SandboxError::Unavailable`] when `fail_if_unavailable = true` and noop would be selected.
pub fn build_sandbox_with_policy(
    strict: bool,
    fail_if_unavailable: bool,
    denied_domains_present: bool,
) -> Result<Box<dyn Sandbox>, SandboxError> {
    #[cfg(target_os = "macos")]
    {
        let _ = (strict, fail_if_unavailable, denied_domains_present);
        Ok(Box::new(MacosSandbox::new()))
    }

    #[cfg(all(target_os = "linux", feature = "sandbox"))]
    {
        let _ = (fail_if_unavailable, denied_domains_present);
        linux::LinuxSandbox::new(strict).map(|s| Box::new(s) as Box<dyn Sandbox>)
    }

    // Noop path: platform without an OS sandbox backend.
    #[cfg(not(any(target_os = "macos", all(target_os = "linux", feature = "sandbox"))))]
    {
        if strict {
            return Err(SandboxError::Unavailable {
                reason: "OS sandbox not supported on this platform and strict=true".into(),
            });
        }
        if fail_if_unavailable {
            return Err(SandboxError::Unavailable {
                reason: "noop backend selected but fail_if_unavailable=true; \
                         OS sandbox is required on this platform"
                    .into(),
            });
        }
        if denied_domains_present {
            tracing::warn!(
                "sandbox.denied_domains is set but the OS sandbox is unavailable on this platform \
                 — denied domains cannot be enforced; set fail_if_unavailable=true to make this a \
                 startup error"
            );
        } else {
            tracing::warn!(
                "OS sandbox not supported on this platform — running without subprocess isolation"
            );
        }
        Ok(Box::new(NoopSandbox))
    }
}

#[cfg(test)]
mod tests {
    #[test]
    #[cfg(not(any(target_os = "macos", all(target_os = "linux", feature = "sandbox"))))]
    fn build_sandbox_strict_fails_when_unsupported() {
        use super::{SandboxError, build_sandbox};
        let err = build_sandbox(true).expect_err("strict must fail on unsupported platform");
        assert!(matches!(err, SandboxError::Unavailable { .. }));
    }

    #[test]
    #[cfg(not(any(target_os = "macos", all(target_os = "linux", feature = "sandbox"))))]
    fn build_sandbox_nonstrict_falls_back_to_noop() {
        use super::build_sandbox;
        let sb = build_sandbox(false).expect("noop fallback ok");
        assert_eq!(sb.name(), "noop");
    }

    #[test]
    fn canonicalize_paths_drops_nonexistent_path() {
        use super::{SandboxPolicy, SandboxProfile};
        use std::path::PathBuf;

        let policy = SandboxPolicy {
            profile: SandboxProfile::Workspace,
            allow_read: vec![PathBuf::from(
                "/this/path/does/not/exist/zeph-test-sentinel",
            )],
            allow_write: vec![],
            allow_network: false,
            allow_exec: vec![],
            env_inherit: vec![],
            denied_domains: vec![],
        }
        .canonicalized();

        assert!(
            policy.allow_read.is_empty(),
            "non-existent path must be dropped by canonicalized()"
        );
    }
}