envseal 0.3.5

//! Shared execution context — the single security control point.
//!
//! Every secret that leaves the vault flows through [`prepare_execution`].
//! It runs all the security checks (hostile-env detection, binary
//! resolution, TOCTOU pinning, hash verification, per-secret authorization,
//! audit logging, decryption) and returns a [`PreparedExecution`] that any
//! execution mode (exec-replace, pipe, supervised) consumes.

use std::path::PathBuf;

use zeroize::Zeroizing;

use crate::error::Error;
use crate::guard;
use crate::gui::{self, Approval};
use crate::policy::{self, Policy};
use crate::vault::Vault;

/// Everything needed to spawn a child with secrets injected.
///
/// Built once via [`prepare_execution`], consumed by any execution mode.
/// Holds a file-descriptor keepalive for TOCTOU prevention; the caller
/// must keep the [`PreparedExecution`] alive across the spawn.
///
/// The pinned file descriptor is intentionally not directly accessible
/// to callers — its `Drop` is what closes the TOCTOU window. The Linux
/// Lockdown supervisor needs the raw fd as an argument to its
/// helper-mode invocation, and reaches it through the dedicated
/// `pinned_target_fd()` accessor that is only compiled on Linux
/// (`#[cfg(target_os = "linux")]`).
pub struct PreparedExecution {
    /// Resolved absolute path to the binary (used for display, audit, `arg0`).
    pub binary_path: String,
    /// Path passed to `Command::new` — `/proc/self/fd/N` on Linux for TOCTOU.
    pub exec_path: String,
    /// Arguments to pass to the binary (`command[1..]`).
    pub args: Vec<String>,
    /// Sanitized environment variables to set on the child.
    pub clean_env: std::collections::HashMap<String, String>,
    /// Decrypted secret env-var pairs (`(env_var_name, secret_value)`).
    pub env_pairs: Vec<(String, Zeroizing<String>)>,
    /// File-descriptor keepalive for TOCTOU prevention. Private — the
    /// `Drop` of the inner `File` is the side effect that matters; the
    /// rust compiler doesn't see field-only-for-drop as a use, hence
    /// the `dead_code` allow on platforms that don't read the fd.
    #[allow(dead_code)]
    pinned_file: Option<std::fs::File>,
}

impl PreparedExecution {
    /// On Linux, return the raw file descriptor of the pinned target
    /// binary so the Lockdown sandbox helper can be told to
    /// `execv("/proc/self/fd/N")` after finishing its mount setup.
    /// Returns `-1` (invalid fd) if no fd was pinned. Other platforms
    /// don't expose this — they pin via path on Windows, via
    /// `pre_exec` on macOS.
    #[cfg(target_os = "linux")]
    #[must_use]
    pub fn pinned_target_fd(&self) -> std::os::fd::RawFd {
        use std::os::fd::AsRawFd;
        self.pinned_file.as_ref().map_or(-1, AsRawFd::as_raw_fd)
    }
}

/// Run all the shared security checks and return everything needed for spawn.
///
/// This is the single security control point: env sanitization, binary
/// resolution, TOCTOU pinning, hash verification, per-secret authorization
/// (with GUI approval if needed), audit logging, and decryption all happen
/// here. The caller chooses how to spawn — exec-replace, pipe, or supervised.
///
/// # Errors
///
/// Returns an error if any security check fails (hostile env, missing
/// binary, hash mismatch, denied approval, decryption failure).
#[allow(clippy::too_many_lines)]
pub fn prepare_execution(
    vault: &Vault,
    mappings: &[(&str, &str)],
    command: &[String],
) -> Result<PreparedExecution, Error> {
    // STEP 1: Load security config
    let mut sec_config =
        crate::security_config::load_config(vault.root(), vault.master_key_bytes())?;

    // STEP 2: GUARD — environment-injection policy (signal taxonomy)
    guard::enforce_env_policy(&sec_config)?;

    // STEP 2b: GUI-environment signals (input injectors, screen
    // recorders, remote desktop, X11) are evaluated on EVERY injection,
    // even when AllowAlways would otherwise skip the popup. Pre-approved
    // rules must not bypass the physical-presence / automation-detection
    // taxonomy — an attacker who obtained shell access while the user is
    // away should not be able to auto-approve via a pre-existing rule.
    let gui_signals = guard::assess_gui_signals(&guard::DetectorContext::ambient());
    guard::emit_signals_inline(gui_signals, &sec_config)?;

    if command.is_empty() {
        return Err(Error::BinaryResolution(
            "no command specified after --".to_string(),
        ));
    }

    // STEP 2b: Validate each requested env var name. Done before resolution
    // so a malformed/blocklisted name is rejected before any I/O.
    for &(_, env_var) in mappings {
        super::inject::validate_env_var_name(env_var)?;
    }

    // STEP 2b'.0: Hard-block the CTF flag from any injection path.
    //
    // The flag exists for ONE legitimate purpose: hash-comparison
    // via `envseal ctf verify <guess>`. There is no scenario in
    // which `inject` / `pipe` / `run` should hand the flag bytes to
    // a child process — even a "trusted" one. The whole CTF claim
    // ("nobody gets it out, not human, not AI, not both together")
    // collapses if a single Allow click on a python script defeats
    // it. Refusing here is not a policy decision the operator can
    // override; the flag is structurally non-injectable.
    //
    // We log this as a `Severity::Critical` signal so the audit
    // trail records every attempt — the CTF status page surfaces
    // attempt counts as part of the "active challenge" view.
    for &(secret_name, _) in mappings {
        if secret_name.eq_ignore_ascii_case("ctf-flag") {
            let _ = crate::audit::log_required(&crate::audit::AuditEvent::SignalRecorded {
                tier: format!("{:?}", sec_config.tier),
                classification: format!(
                    "critical [ctf.flag.injection_attempt] refused to inject 'ctf-flag' \
                     into '{}' — flag is structurally non-injectable",
                    command.first().map_or("<no-command>", String::as_str)
                ),
            });
            return Err(Error::EnvironmentCompromised(
                "ctf-flag is non-injectable by design. The CTF flag exists only \
                 for `envseal ctf verify` hash comparison; envseal refuses to \
                 hand its plaintext to any child process. Run `envseal ctf reset` \
                 to clear the challenge."
                    .to_string(),
            ));
        }
    }

    // STEP 2c: Preflight — all referenced secrets must exist in the
    // vault before we ask the user to approve anything. The previous
    // form discovered missing secrets only during phase-2 decrypt,
    // AFTER the operator clicked through approvals + a challenge
    // gate for the OTHER secrets. With several secrets in a
    // `.envseal` mapping, hitting one stale/revoked entry made every
    // click on the others wasted (and pre-the-policy-save fix, even
    // re-prompted on the next run). Surface missing secrets up front
    // with the env-var name so the user knows exactly which mapping
    // line to fix.
    let missing: Vec<String> = mappings
        .iter()
        .filter(|(name, _)| !vault.has_secret(name))
        .map(|(name, env_var)| format!("{env_var}={name}"))
        .collect();
    if !missing.is_empty() {
        return Err(Error::SecretNotFound(format!(
            "the following .envseal mapping(s) reference secrets that aren't in the vault: \
             {} — store them with `envseal store <name>` or remove the line(s) from .envseal",
            missing.join(", ")
        )));
    }

    // STEP 3: Resolve binary
    let binary_path = policy::resolve_binary(&command[0])?;

    // STEP 4: Load AEAD-sealed policy. `load_sealed` returns
    // `Policy::default()` when neither sealed nor legacy file is
    // present, so a fresh vault still works without policy.
    let policy_path = vault.policy_path();
    let mut policy = Policy::load_sealed(&policy_path, vault.master_key_bytes())?;
    if policy.generation < sec_config.policy_generation {
        return Err(Error::EnvironmentCompromised(format!(
            "policy rollback detected: loaded generation {} is older than expected {}",
            policy.generation, sec_config.policy_generation
        )));
    }

    // STEP 5: TOCTOU pin — open the binary now, exec the fd later
    let binary_path_buf = PathBuf::from(&binary_path);
    #[allow(unused_mut, unused_assignments)]
    let mut exec_path = binary_path.clone();
    #[allow(unused_mut, unused_assignments)]
    let mut kept_alive_file: Option<std::fs::File> = None;

    #[cfg(target_os = "linux")]
    {
        use std::os::unix::fs::OpenOptionsExt;
        use std::os::unix::io::AsRawFd;
        let file = std::fs::OpenOptions::new()
            .read(true)
            .custom_flags(libc::O_NOFOLLOW | libc::O_CLOEXEC)
            .open(&binary_path_buf)
            .map_err(|e| {
                Error::BinaryResolution(format!("failed to open binary for TOCTOU prevention: {e}"))
            })?;
        exec_path = format!("/proc/self/fd/{}", file.as_raw_fd());
        kept_alive_file = Some(file);
    }

    #[cfg(all(unix, not(target_os = "linux")))]
    {
        use std::os::unix::fs::OpenOptionsExt;
        use std::os::unix::io::AsRawFd;
        let file = std::fs::OpenOptions::new()
            .read(true)
            .custom_flags(libc::O_NOFOLLOW | libc::O_CLOEXEC)
            .open(&binary_path_buf)
            .map_err(|e| {
                Error::BinaryResolution(format!("failed to open binary for TOCTOU prevention: {e}"))
            })?;
        exec_path = format!("/dev/fd/{}", file.as_raw_fd());
        kept_alive_file = Some(file);
    }

    #[cfg(windows)]
    {
        // On Windows we can't exec via a fd path, but we CAN keep a
        // restrictive-share handle open during spawn to prevent the file
        // from being deleted or replaced between hash verification and
        // CreateProcessW.
        use std::os::windows::ffi::OsStrExt;
        use std::os::windows::io::FromRawHandle;
        use windows_sys::Win32::Foundation::INVALID_HANDLE_VALUE;
        use windows_sys::Win32::Storage::FileSystem::{
            CreateFileW, FILE_ATTRIBUTE_NORMAL, FILE_SHARE_READ, OPEN_EXISTING,
        };
        let wide: Vec<u16> = binary_path_buf
            .as_os_str()
            .encode_wide()
            .chain(std::iter::once(0))
            .collect();
        let handle = unsafe {
            CreateFileW(
                wide.as_ptr(),
                0x8000_0000,     // GENERIC_READ
                FILE_SHARE_READ, // deny write/delete while we hold the handle
                std::ptr::null_mut(),
                OPEN_EXISTING,
                FILE_ATTRIBUTE_NORMAL,
                std::ptr::null_mut(),
            )
        };
        if handle == INVALID_HANDLE_VALUE {
            return Err(Error::BinaryResolution(format!(
                "failed to open binary for TOCTOU prevention: {}",
                std::io::Error::last_os_error()
            )));
        }
        let file = unsafe { std::fs::File::from_raw_handle(handle.cast::<std::ffi::c_void>()) };
        exec_path.clone_from(&binary_path);
        kept_alive_file = Some(file);
    }

    // STEP 6: Verify binary hash if stored in policy
    if let Some(stored_hash) = policy.binary_hash(&binary_path) {
        if let Some(ref mut file) = kept_alive_file {
            guard::verify_file_hash(file, &stored_hash, &binary_path_buf)?;
        } else {
            guard::verify_binary_hash(&binary_path_buf, &stored_hash)?;
        }
    }

    // STEP 7: Per-secret authorization + decryption.
    //
    // Authorization is argv-bound: the rule we look up (and the rule we
    // store on AllowAlways) is keyed by `(binary, secret, fingerprint)`,
    // where the fingerprint is computed from `command[1..]`. An approval
    // for `wrangler deploy` therefore does NOT auto-allow `wrangler
    // --shell evil.sh` on the next run.
    let fingerprint_str = super::inject::command_fingerprint(command);
    let fingerprint_for_lookup = if fingerprint_str.is_empty() {
        None
    } else {
        Some(fingerprint_str.as_str())
    };

    // Pre-compute the binary hash so every authorization check can
    // verify the binary hasn't been replaced since approval.
    let mut current_hash: Option<String> = None;

    // Two-phase split: collect approvals first, persist policy
    // BEFORE any decrypt runs, then decrypt + inject. The previous
    // single-loop form lost every Allow Always click if any secret
    // failed to decrypt — operator clicks "Allow Always" three times
    // for three secrets, the fourth has been revoked, decrypt fails,
    // function returns, the three Allow Always rules are vaporized,
    // next invocation re-prompts for all of them. Splitting the
    // phases means an Allow Always is durable the moment the user
    // clicks it, regardless of what fails downstream.
    let mut policy_dirty = false;
    for &(secret_name, env_var) in mappings {
        if current_hash.is_none() {
            let hash = if let Some(ref mut file) = kept_alive_file {
                guard::hash_open_file(file)?
            } else {
                guard::hash_binary(std::path::Path::new(&binary_path))?
            };
            current_hash = Some(hash);
        }
        if policy.is_authorized_with_hash_and_args(
            &binary_path,
            secret_name,
            fingerprint_for_lookup,
            current_hash.as_deref(),
        ) {
            continue;
        }
        let approval =
            gui::request_approval(&binary_path, command, secret_name, env_var, &sec_config)?;
        match approval {
            Approval::AllowOnce => {}
            Approval::AllowAlways => {
                let hash = current_hash.as_deref().unwrap_or("");
                // Apply tier-driven default expiry, then clamp to
                // the configured max. CTF mode sets max=600s so
                // every CTF-window approval is short-lived even if
                // the operator clicks "Allow Forever". Standard
                // tier with no expiry config falls through to a
                // forever rule (current default behaviour).
                let now = std::time::SystemTime::now()
                    .duration_since(std::time::UNIX_EPOCH)
                    .map_or(0, |d| d.as_secs());
                let default_expiry = sec_config.default_rule_expiry_secs;
                let max_expiry = sec_config.max_rule_expiry_secs;
                let effective_expiry = match (default_expiry, max_expiry) {
                    (None, None) => None,
                    (Some(d), None) => Some(d),
                    (None, Some(m)) => Some(m),
                    (Some(d), Some(m)) => Some(d.min(m)),
                };
                if let Some(secs) = effective_expiry {
                    policy.allow_key_with_expiry(
                        &binary_path,
                        secret_name,
                        hash,
                        fingerprint_for_lookup.map(str::to_string),
                        now.saturating_add(secs),
                    );
                } else {
                    policy.allow_key_with_hash_and_args(
                        &binary_path,
                        secret_name,
                        hash,
                        fingerprint_for_lookup.map(str::to_string),
                    );
                }
                policy_dirty = true;
            }
            Approval::Deny => {
                // Persist any Allow Always rules approved earlier in
                // this batch even if a later secret was denied —
                // throwing them away on Deny would surprise the user
                // ("I just clicked Allow Always twice, why am I being
                // re-prompted?").
                if policy_dirty {
                    policy.save_sealed(&policy_path, vault.master_key_bytes())?;
                    sec_config.policy_generation = policy.generation;
                    crate::security_config::save_config(
                        vault.root(),
                        &sec_config,
                        vault.master_key_bytes(),
                    )?;
                }
                return Err(Error::UserDenied);
            }
        }
    }
    if policy_dirty {
        policy.save_sealed(&policy_path, vault.master_key_bytes())?;
        sec_config.policy_generation = policy.generation;
        crate::security_config::save_config(vault.root(), &sec_config, vault.master_key_bytes())?;
    }

    // Phase 2: decrypt + inject. By this point every Allow Always is
    // already on disk, so a decrypt failure here is recoverable —
    // the user fixes the missing secret and re-runs without
    // re-clicking anything.
    let mut env_pairs: Vec<(String, Zeroizing<String>)> = Vec::with_capacity(mappings.len());
    for &(secret_name, env_var) in mappings {
        let plaintext = vault.decrypt(secret_name)?;
        let value = Zeroizing::new(String::from_utf8(plaintext.to_vec()).map_err(|e| {
            Error::CryptoFailure(format!("secret '{secret_name}' is not valid UTF-8: {e}"))
        })?);
        env_pairs.push((env_var.to_string(), value));
    }

    // STEP 8: Audit log every secret access
    crate::audit::log_required(&crate::audit::AuditEvent::SecretAccessed {
        binary: binary_path.clone(),
        secret: mappings
            .iter()
            .map(|(s, _)| (*s).to_string())
            .collect::<Vec<_>>()
            .join(","),
    })?;

    // STEP 9: Build sanitized environment for the child
    let clean_env = guard::sanitized_env();

    Ok(PreparedExecution {
        binary_path,
        exec_path,
        args: command[1..].to_vec(),
        clean_env,
        env_pairs,
        pinned_file: kept_alive_file,
    })
}

/// Hardening that runs in the child between `fork()` and `exec()`.
///
/// **Must only use async-signal-safe operations** — no allocation, no
/// `std::fs`, no panic, no `eprintln`. Three syscalls:
///
/// - `prctl(PR_SET_DUMPABLE, 0)` — block ptrace and `/proc/<pid>/mem`.
/// - `setrlimit(RLIMIT_CORE, 0)` — defeat core dumps.
/// - `prctl(PR_SET_NO_NEW_PRIVS, 1)` — prevent suid escalation in child.
///
/// # Errors
///
/// Returns the OS error if any of the three syscalls fail.
#[cfg(target_os = "linux")]
pub fn harden_child_process_inner() -> std::io::Result<()> {
    unsafe {
        if libc::prctl(libc::PR_SET_DUMPABLE, 0) < 0 {
            return Err(std::io::Error::last_os_error());
        }
        let rlimit = libc::rlimit {
            rlim_cur: 0,
            rlim_max: 0,
        };
        if libc::setrlimit(libc::RLIMIT_CORE, &rlimit) < 0 {
            return Err(std::io::Error::last_os_error());
        }
        if libc::prctl(libc::PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) < 0 {
            return Err(std::io::Error::last_os_error());
        }
    }
    Ok(())
}

/// No-op child hardening on non-Linux platforms.
///
/// # Errors
/// Never errors on non-Linux platforms.
#[cfg(not(target_os = "linux"))]
pub fn harden_child_process_inner() -> std::io::Result<()> {
    Ok(())
}