codex/codex-rs/core/src/exec.rs

#[cfg(unix)]
use std::os::unix::process::ExitStatusExt;

use std::collections::HashMap;
use std::io;
use std::path::Path;
use std::path::PathBuf;
use std::process::ExitStatus;
use std::process::Stdio;
use std::sync::Arc;
use std::time::Duration;
use std::time::Instant;

use tokio::io::AsyncRead;
use tokio::io::AsyncReadExt;
use tokio::io::BufReader;
use tokio::process::Child;
use tokio::process::Command;
use tokio::sync::Notify;

use crate::error::CodexErr;
use crate::error::Result;
use crate::error::SandboxErr;
use crate::exec_linux::exec_linux;
use crate::protocol::SandboxPolicy;

// Maximum we send for each stream, which is either:
// - 10KiB OR
// - 256 lines
const MAX_STREAM_OUTPUT: usize = 10 * 1024;
const MAX_STREAM_OUTPUT_LINES: usize = 256;

const DEFAULT_TIMEOUT_MS: u64 = 10_000;

// Hardcode these since it does not seem worth including the libc crate just
// for these.
const SIGKILL_CODE: i32 = 9;
const TIMEOUT_CODE: i32 = 64;

const MACOS_SEATBELT_BASE_POLICY: &str = include_str!("seatbelt_base_policy.sbpl");

/// When working with `sandbox-exec`, only consider `sandbox-exec` in `/usr/bin`
/// to defend against an attacker trying to inject a malicious version on the
/// PATH. If /usr/bin/sandbox-exec has been tampered with, then the attacker
/// already has root access.
const MACOS_PATH_TO_SEATBELT_EXECUTABLE: &str = "/usr/bin/sandbox-exec";

/// Experimental environment variable that will be set to some non-empty value
/// if both of the following are true:
///
/// 1. The process was spawned by Codex as part of a shell tool call.
/// 2. SandboxPolicy.has_full_network_access() was false for the tool call.
///
/// We may try to have just one environment variable for all sandboxing
/// attributes, so this may change in the future.
pub const CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR: &str = "CODEX_SANDBOX_NETWORK_DISABLED";

#[derive(Debug, Clone)]
pub struct ExecParams {
    pub command: Vec<String>,
    pub cwd: PathBuf,
    pub timeout_ms: Option<u64>,
    pub env: HashMap<String, String>,
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub enum SandboxType {
    None,

    /// Only available on macOS.
    MacosSeatbelt,

    /// Only available on Linux.
    LinuxSeccomp,
}

pub async fn process_exec_tool_call(
    params: ExecParams,
    sandbox_type: SandboxType,
    ctrl_c: Arc<Notify>,
    sandbox_policy: &SandboxPolicy,
) -> Result<ExecToolCallOutput> {
    let start = Instant::now();

    let raw_output_result = match sandbox_type {
        SandboxType::None => exec(params, sandbox_policy, ctrl_c).await,
        SandboxType::MacosSeatbelt => {
            let ExecParams {
                command,
                cwd,
                timeout_ms,
                env,
            } = params;
            let child = spawn_command_under_seatbelt(
                command,
                sandbox_policy,
                cwd,
                StdioPolicy::RedirectForShellTool,
                env,
            )
            .await?;
            consume_truncated_output(child, ctrl_c, timeout_ms).await
        }
        SandboxType::LinuxSeccomp => exec_linux(params, ctrl_c, sandbox_policy),
    };
    let duration = start.elapsed();
    match raw_output_result {
        Ok(raw_output) => {
            let stdout = String::from_utf8_lossy(&raw_output.stdout).to_string();
            let stderr = String::from_utf8_lossy(&raw_output.stderr).to_string();

            #[cfg(target_family = "unix")]
            match raw_output.exit_status.signal() {
                Some(TIMEOUT_CODE) => return Err(CodexErr::Sandbox(SandboxErr::Timeout)),
                Some(signal) => {
                    return Err(CodexErr::Sandbox(SandboxErr::Signal(signal)));
                }
                None => {}
            }

            let exit_code = raw_output.exit_status.code().unwrap_or(-1);

            // NOTE(ragona): This is much less restrictive than the previous check. If we exec
            // a command, and it returns anything other than success, we assume that it may have
            // been a sandboxing error and allow the user to retry. (The user of course may choose
            // not to retry, or in a non-interactive mode, would automatically reject the approval.)
            if exit_code != 0 && sandbox_type != SandboxType::None {
                return Err(CodexErr::Sandbox(SandboxErr::Denied(
                    exit_code, stdout, stderr,
                )));
            }

            Ok(ExecToolCallOutput {
                exit_code,
                stdout,
                stderr,
                duration,
            })
        }
        Err(err) => {
            tracing::error!("exec error: {err}");
            Err(err)
        }
    }
}

pub async fn spawn_command_under_seatbelt(
    command: Vec<String>,
    sandbox_policy: &SandboxPolicy,
    cwd: PathBuf,
    stdio_policy: StdioPolicy,
    env: HashMap<String, String>,
) -> std::io::Result<Child> {
    let seatbelt_command = create_seatbelt_command(command, sandbox_policy, &cwd);
    spawn_child_async(seatbelt_command, cwd, sandbox_policy, stdio_policy, env).await
}

fn create_seatbelt_command(
    command: Vec<String>,
    sandbox_policy: &SandboxPolicy,
    cwd: &Path,
) -> Vec<String> {
    let (file_write_policy, extra_cli_args) = {
        if sandbox_policy.has_full_disk_write_access() {
            // Allegedly, this is more permissive than `(allow file-write*)`.
            (
                r#"(allow file-write* (regex #"^/"))"#.to_string(),
                Vec::<String>::new(),
            )
        } else {
            let writable_roots = sandbox_policy.get_writable_roots_with_cwd(cwd);
            let (writable_folder_policies, cli_args): (Vec<String>, Vec<String>) = writable_roots
                .iter()
                .enumerate()
                .map(|(index, root)| {
                    let param_name = format!("WRITABLE_ROOT_{index}");
                    let policy: String = format!("(subpath (param \"{param_name}\"))");
                    let cli_arg = format!("-D{param_name}={}", root.to_string_lossy());
                    (policy, cli_arg)
                })
                .unzip();
            if writable_folder_policies.is_empty() {
                ("".to_string(), Vec::<String>::new())
            } else {
                let file_write_policy = format!(
                    "(allow file-write*\n{}\n)",
                    writable_folder_policies.join(" ")
                );
                (file_write_policy, cli_args)
            }
        }
    };

    let file_read_policy = if sandbox_policy.has_full_disk_read_access() {
        "; allow read-only file operations\n(allow file-read*)"
    } else {
        ""
    };

    // TODO(mbolin): apply_patch calls must also honor the SandboxPolicy.
    let network_policy = if sandbox_policy.has_full_network_access() {
        "(allow network-outbound)\n(allow network-inbound)\n(allow system-socket)"
    } else {
        ""
    };

    let full_policy = format!(
        "{MACOS_SEATBELT_BASE_POLICY}\n{file_read_policy}\n{file_write_policy}\n{network_policy}"
    );
    let mut seatbelt_command: Vec<String> = vec![
        MACOS_PATH_TO_SEATBELT_EXECUTABLE.to_string(),
        "-p".to_string(),
        full_policy,
    ];
    seatbelt_command.extend(extra_cli_args);
    seatbelt_command.push("--".to_string());
    seatbelt_command.extend(command);
    seatbelt_command
}

#[derive(Debug)]
pub struct RawExecToolCallOutput {
    pub exit_status: ExitStatus,
    pub stdout: Vec<u8>,
    pub stderr: Vec<u8>,
}

#[derive(Debug)]
pub struct ExecToolCallOutput {
    pub exit_code: i32,
    pub stdout: String,
    pub stderr: String,
    pub duration: Duration,
}

async fn exec(
    ExecParams {
        command,
        cwd,
        timeout_ms,
        env,
    }: ExecParams,
    sandbox_policy: &SandboxPolicy,
    ctrl_c: Arc<Notify>,
) -> Result<RawExecToolCallOutput> {
    let child = spawn_child_async(
        command,
        cwd,
        sandbox_policy,
        StdioPolicy::RedirectForShellTool,
        env,
    )
    .await?;
    consume_truncated_output(child, ctrl_c, timeout_ms).await
}

#[derive(Debug, Clone, Copy)]
pub enum StdioPolicy {
    RedirectForShellTool,
    Inherit,
}

macro_rules! configure_command {
    (
        $cmd_type: path,
        $command: expr,
        $cwd: expr,
        $sandbox_policy: expr,
        $stdio_policy: expr,
        $env_map: expr
    ) => {{
        // For now, we take `SandboxPolicy` as a parameter to spawn_child() because
        // we need to determine whether to set the
        // `CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR` environment variable.
        // Ultimately, we should be stricter about the environment variables that
        // are set for the command (as we are when spawning an MCP server), so
        // instead of SandboxPolicy, we should take the exact env to use for the
        // Command (i.e., `env_clear().envs(env)`).
        if $command.is_empty() {
            return Err(io::Error::new(
                io::ErrorKind::InvalidInput,
                "command args are empty",
            ));
        }

        let mut cmd = <$cmd_type>::new(&$command[0]);
        cmd.args(&$command[1..]);
        cmd.current_dir($cwd);

        // Previously, to update the env for `cmd`, we did the straightforward
        // thing of calling `env_clear()` followed by `envs(&env_map)` so
        // that the spawned process inherited *only* the variables explicitly
        // provided by the caller. On Linux, the combination of `env_clear()`
        // and Landlock/seccomp caused a permission error whereas this more
        // "surgical" approach of setting variables individually appears to
        // work fine. More time with `strace` and friends is merited to fully
        // debug thus, though we will soon use a helper binary like we do for
        // Seatbelt, which will simplify this logic.

        // Iterate through the current process environment first so we can
        // decide, for every variable that already exists, whether we need to
        // override its value.
        let mut remaining_overrides = $env_map.clone();
        for (key, current_val) in std::env::vars() {
            if let Some(desired_val) = remaining_overrides.remove(&key) {
                // The caller provided a value for this variable. Override it
                // only if the value differs from what is currently set.
                if desired_val != current_val {
                    cmd.env(&key, desired_val);
                }
            }
            // If the variable was not in `env_map`, we leave it unchanged.
        }

        // Any entries still left in `remaining_overrides` were not present in
        // the parent environment. Add them now so that the child process sees
        // the complete set requested by the caller.
        for (key, val) in remaining_overrides {
            cmd.env(key, val);
        }

        if !$sandbox_policy.has_full_network_access() {
            cmd.env(CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR, "1");
        }

        match $stdio_policy {
            StdioPolicy::RedirectForShellTool => {
                // Do not create a file descriptor for stdin because otherwise some
                // commands may hang forever waiting for input. For example, ripgrep has
                // a heuristic where it may try to read from stdin as explained here:
                // https://github.com/BurntSushi/ripgrep/blob/e2362d4d5185d02fa857bf381e7bd52e66fafc73/crates/core/flags/hiargs.rs#L1101-L1103
                cmd.stdin(Stdio::null());

                cmd.stdout(Stdio::piped()).stderr(Stdio::piped());
            }
            StdioPolicy::Inherit => {
                // Inherit stdin, stdout, and stderr from the parent process.
                cmd.stdin(Stdio::inherit())
                    .stdout(Stdio::inherit())
                    .stderr(Stdio::inherit());
            }
        }

        std::io::Result::<$cmd_type>::Ok(cmd)
    }};
}

/// Spawns the appropriate child process for the ExecParams and SandboxPolicy,
/// ensuring the args and environment variables used to create the `Command`
/// (and `Child`) honor the configuration.
pub(crate) async fn spawn_child_async(
    command: Vec<String>,
    cwd: PathBuf,
    sandbox_policy: &SandboxPolicy,
    stdio_policy: StdioPolicy,
    env: HashMap<String, String>,
) -> std::io::Result<Child> {
    let mut cmd = configure_command!(Command, command, cwd, sandbox_policy, stdio_policy, env)?;
    cmd.kill_on_drop(true).spawn()
}

/// Alternative version of `spawn_child_async()` that returns
/// `std::process::Child` instead of `tokio::process::Child`. This is useful for
/// spawning a child process in a thread that is not running a Tokio runtime.
pub fn spawn_child_sync(
    command: Vec<String>,
    cwd: PathBuf,
    sandbox_policy: &SandboxPolicy,
    stdio_policy: StdioPolicy,
    env: HashMap<String, String>,
) -> std::io::Result<std::process::Child> {
    let mut cmd = configure_command!(
        std::process::Command,
        command,
        cwd,
        sandbox_policy,
        stdio_policy,
        env
    )?;
    cmd.spawn()
}

/// Consumes the output of a child process, truncating it so it is suitable for
/// use as the output of a `shell` tool call. Also enforces specified timeout.
pub(crate) async fn consume_truncated_output(
    mut child: Child,
    ctrl_c: Arc<Notify>,
    timeout_ms: Option<u64>,
) -> Result<RawExecToolCallOutput> {
    // Both stdout and stderr were configured with `Stdio::piped()`
    // above, therefore `take()` should normally return `Some`.  If it doesn't
    // we treat it as an exceptional I/O error

    let stdout_reader = child.stdout.take().ok_or_else(|| {
        CodexErr::Io(io::Error::other(
            "stdout pipe was unexpectedly not available",
        ))
    })?;
    let stderr_reader = child.stderr.take().ok_or_else(|| {
        CodexErr::Io(io::Error::other(
            "stderr pipe was unexpectedly not available",
        ))
    })?;

    let stdout_handle = tokio::spawn(read_capped(
        BufReader::new(stdout_reader),
        MAX_STREAM_OUTPUT,
        MAX_STREAM_OUTPUT_LINES,
    ));
    let stderr_handle = tokio::spawn(read_capped(
        BufReader::new(stderr_reader),
        MAX_STREAM_OUTPUT,
        MAX_STREAM_OUTPUT_LINES,
    ));

    let interrupted = ctrl_c.notified();
    let timeout = Duration::from_millis(timeout_ms.unwrap_or(DEFAULT_TIMEOUT_MS));
    let exit_status = tokio::select! {
        result = tokio::time::timeout(timeout, child.wait()) => {
            match result {
                Ok(Ok(exit_status)) => exit_status,
                Ok(e) => e?,
                Err(_) => {
                    // timeout
                    child.start_kill()?;
                    // Debatable whether `child.wait().await` should be called here.
                    synthetic_exit_status(128 + TIMEOUT_CODE)
                }
            }
        }
        _ = interrupted => {
            child.start_kill()?;
            synthetic_exit_status(128 + SIGKILL_CODE)
        }
    };

    let stdout = stdout_handle.await??;
    let stderr = stderr_handle.await??;

    Ok(RawExecToolCallOutput {
        exit_status,
        stdout,
        stderr,
    })
}

async fn read_capped<R: AsyncRead + Unpin>(
    mut reader: R,
    max_output: usize,
    max_lines: usize,
) -> io::Result<Vec<u8>> {
    let mut buf = Vec::with_capacity(max_output.min(8 * 1024));
    let mut tmp = [0u8; 8192];

    let mut remaining_bytes = max_output;
    let mut remaining_lines = max_lines;

    loop {
        let n = reader.read(&mut tmp).await?;
        if n == 0 {
            break;
        }

        // Copy into the buffer only while we still have byte and line budget.
        if remaining_bytes > 0 && remaining_lines > 0 {
            let mut copy_len = 0;
            for &b in &tmp[..n] {
                if remaining_bytes == 0 || remaining_lines == 0 {
                    break;
                }
                copy_len += 1;
                remaining_bytes -= 1;
                if b == b'\n' {
                    remaining_lines -= 1;
                }
            }
            buf.extend_from_slice(&tmp[..copy_len]);
        }
        // Continue reading to EOF to avoid back-pressure, but discard once caps are hit.
    }

    Ok(buf)
}

#[cfg(unix)]
fn synthetic_exit_status(code: i32) -> ExitStatus {
    use std::os::unix::process::ExitStatusExt;
    std::process::ExitStatus::from_raw(code)
}

#[cfg(windows)]
fn synthetic_exit_status(code: i32) -> ExitStatus {
    use std::os::windows::process::ExitStatusExt;
    #[expect(clippy::unwrap_used)]
    std::process::ExitStatus::from_raw(code.try_into().unwrap())
}