| 1 | //! Process hardening for Linux sandbox defense-in-depth (#2183). |
| 2 | //! |
| 3 | //! This module applies kernel-level restrictions to the codewhale-tui process |
| 4 | //! itself. These hardening measures protect the *parent* TUI process and its |
| 5 | //! descendants from information leaks and privilege-escalation vectors; they |
| 6 | //! are not a filesystem or network sandbox for child commands. The seccomp |
| 7 | //! source module is not wired into child execution yet. |
| 8 | //! |
| 9 | //! # Ordering constraints |
| 10 | //! |
| 11 | //! `apply_process_hardening()` MUST be called **before** the Tokio runtime is |
| 12 | //! booted and **before** any worker threads are spawned. The reasons: |
| 13 | //! |
| 14 | //! 1. `PR_SET_DUMPABLE` — once set to 0, the process cannot be ptraced and |
| 15 | //! `/proc/self/` becomes root-owned. This must happen before any threads |
| 16 | //! exist, because the kernel applies dumpable state per-thread-group and |
| 17 | //! changing it after threads are live can race with `/proc` lookups. |
| 18 | //! |
| 19 | //! 2. `PR_SET_NO_NEW_PRIVS` — prevents the process and all descendants from |
| 20 | //! ever gaining new privileges via setuid/setgid/fscaps. This is |
| 21 | //! irreversible and must be applied before executing any helper binaries or |
| 22 | //! subprocesses that might (incorrectly) rely on privilege boundaries. |
| 23 | //! |
| 24 | //! 3. `RLIMIT_CORE` — disables core dumps so that sensitive in-memory data |
| 25 | //! (API keys, tokens, prompt content) is never written to disk on a crash. |
| 26 | //! Setting this before any data is loaded into memory is the safest posture. |
| 27 | //! |
| 28 | //! # Platform support |
| 29 | //! |
| 30 | //! These hardening measures are Linux-only (they use `prctl` and `setrlimit` |
| 31 | //! from the `libc` crate). On non-Linux platforms, `apply_process_hardening()` |
| 32 | //! is a no-op that logs a debug-level message. |
| 33 | |
| 34 | /// Apply process-level hardening measures. |
| 35 | /// |
| 36 | /// On Linux, this: |
| 37 | /// - Sets `PR_SET_DUMPABLE` to 0 (prevents ptrace, core dumps) |
| 38 | /// - Sets `PR_SET_NO_NEW_PRIVS` to 1 (irreversible no-new-privileges) |
| 39 | /// - Sets `RLIMIT_CORE` to 0 (disables core dumps) |
| 40 | /// |
| 41 | /// On non-Linux platforms this is a no-op. |
| 42 | /// |
| 43 | /// # Panics |
| 44 | /// |
| 45 | /// Does NOT panic. Failures are logged via `tracing::warn` because the |
| 46 | /// hardening is defense-in-depth. A failure does not abort startup or change |
| 47 | /// whether a separately configured Seatbelt/bubblewrap command wrapper is |
| 48 | /// available. |
| 49 | pub fn apply_process_hardening() { |
| 50 | #[cfg(all(target_os = "linux", not(target_env = "ohos")))] |
| 51 | { |
| 52 | apply_linux_hardening(); |
| 53 | } |
| 54 | #[cfg(not(all(target_os = "linux", not(target_env = "ohos"))))] |
| 55 | { |
| 56 | tracing::debug!("Process hardening skipped: not on Linux"); |
| 57 | } |
| 58 | } |
| 59 | |
| 60 | /// Linux-specific hardening implementation. |
| 61 | #[cfg(all(target_os = "linux", not(target_env = "ohos")))] |
| 62 | fn apply_linux_hardening() { |
| 63 | // ── PR_SET_DUMPABLE = 0 ──────────────────────────────────────────────── |
| 64 | // |
| 65 | // When dumpable is 0: |
| 66 | // - The process cannot be ptraced by non-root |
| 67 | // - /proc/<pid>/ becomes owned by root:root (mode 0400) |
| 68 | // - No core dumps are produced |
| 69 | // |
| 70 | // Pattern from openai/codex codex-rs/codex-sandbox/src/linux.rs; reimplemented. |
| 71 | // |
| 72 | // Safety: prctl with PR_SET_DUMPABLE modifies only the calling process. |
| 73 | let result = unsafe { libc::prctl(libc::PR_SET_DUMPABLE, 0i64, 0i64, 0i64, 0i64) }; |
| 74 | if result != 0 { |
| 75 | let err = std::io::Error::last_os_error(); |
| 76 | tracing::warn!( |
| 77 | "PR_SET_DUMPABLE failed ({}); continuing without this hardening", |
| 78 | err |
| 79 | ); |
| 80 | } else { |
| 81 | tracing::debug!("PR_SET_DUMPABLE=0 applied"); |
| 82 | } |
| 83 | |
| 84 | // ── PR_SET_NO_NEW_PRIVS = 1 ──────────────────────────────────────────── |
| 85 | // |
| 86 | // Once set, neither this process nor any descendant can ever gain new |
| 87 | // privileges via setuid, setgid, file capabilities, or LSMs like SELinux |
| 88 | // transitions. This is the strongest anti-escalation primitive the kernel |
| 89 | // offers. |
| 90 | // |
| 91 | // Pattern from openai/codex codex-rs/codex-sandbox/src/linux.rs; reimplemented. |
| 92 | // |
| 93 | // Safety: prctl with PR_SET_NO_NEW_PRIVS modifies only the calling process |
| 94 | // and its future descendants. |
| 95 | let result = unsafe { libc::prctl(libc::PR_SET_NO_NEW_PRIVS, 1i64, 0i64, 0i64, 0i64) }; |
| 96 | if result != 0 { |
| 97 | let err = std::io::Error::last_os_error(); |
| 98 | tracing::warn!( |
| 99 | "PR_SET_NO_NEW_PRIVS failed ({}); continuing without this hardening", |
| 100 | err |
| 101 | ); |
| 102 | } else { |
| 103 | tracing::debug!("PR_SET_NO_NEW_PRIVS=1 applied"); |
| 104 | } |
| 105 | |
| 106 | // ── RLIMIT_CORE = 0 ──────────────────────────────────────────────────── |
| 107 | // |
| 108 | // Disables core dumps at the rlimit level. In combination with |
| 109 | // PR_SET_DUMPABLE=0, this provides a belt-and-suspenders guarantee that |
| 110 | // no core file will ever be written. |
| 111 | // |
| 112 | // Safety: setrlimit modifies resource limits for the calling process only. |
| 113 | let rlim_core = libc::rlimit { |
| 114 | rlim_cur: 0, |
| 115 | rlim_max: 0, |
| 116 | }; |
| 117 | let result = unsafe { libc::setrlimit(libc::RLIMIT_CORE, &raw const rlim_core) }; |
| 118 | if result != 0 { |
| 119 | let err = std::io::Error::last_os_error(); |
| 120 | tracing::warn!( |
| 121 | "RLIMIT_CORE failed ({}); continuing without this hardening", |
| 122 | err |
| 123 | ); |
| 124 | } else { |
| 125 | tracing::debug!("RLIMIT_CORE=0 applied"); |
| 126 | } |
| 127 | } |
| 128 | |
| 129 | #[cfg(test)] |
| 130 | mod tests { |
| 131 | use super::*; |
| 132 | |
| 133 | #[test] |
| 134 | fn test_apply_process_hardening_does_not_panic() { |
| 135 | // This test exists to ensure the function can be called without |
| 136 | // panicking, even on platforms where hardening is a no-op. |
| 137 | apply_process_hardening(); |
| 138 | } |
| 139 | } |
| 140 |