chore: move pre_main_hardening() utility into its own crate (#4403)

codex-rs/process-hardening/src/lib.rs

@@ -0,0 +1,114 @@
+/// This is designed to be called pre-main() (using `#[ctor::ctor]`) to perform
+/// various process hardening steps, such as
+/// - disabling core dumps
+/// - disabling ptrace attach on Linux and macOS.
+/// - removing dangerous environment variables such as LD_PRELOAD and DYLD_*
+pub fn pre_main_hardening() {
+    #[cfg(any(target_os = "linux", target_os = "android"))]
+    pre_main_hardening_linux();
+
+    #[cfg(target_os = "macos")]
+    pre_main_hardening_macos();
+
+    #[cfg(windows)]
+    pre_main_hardening_windows();
+}
+
+#[cfg(any(target_os = "linux", target_os = "android"))]
+const PRCTL_FAILED_EXIT_CODE: i32 = 5;
+
+#[cfg(target_os = "macos")]
+const PTRACE_DENY_ATTACH_FAILED_EXIT_CODE: i32 = 6;
+
+#[cfg(any(target_os = "linux", target_os = "android", target_os = "macos"))]
+const SET_RLIMIT_CORE_FAILED_EXIT_CODE: i32 = 7;
+
+#[cfg(any(target_os = "linux", target_os = "android"))]
+pub(crate) fn pre_main_hardening_linux() {
+    // Disable ptrace attach / mark process non-dumpable.
+    let ret_code = unsafe { libc::prctl(libc::PR_SET_DUMPABLE, 0, 0, 0, 0) };
+    if ret_code != 0 {
+        eprintln!(
+            "ERROR: prctl(PR_SET_DUMPABLE, 0) failed: {}",
+            std::io::Error::last_os_error()
+        );
+        std::process::exit(PRCTL_FAILED_EXIT_CODE);
+    }
+
+    // For "defense in depth," set the core file size limit to 0.
+    set_core_file_size_limit_to_zero();
+
+    // Official Codex releases are MUSL-linked, which means that variables such
+    // as LD_PRELOAD are ignored anyway, but just to be sure, clear them here.
+    let ld_keys: Vec<String> = std::env::vars()
+        .filter_map(|(key, _)| {
+            if key.starts_with("LD_") {
+                Some(key)
+            } else {
+                None
+            }
+        })
+        .collect();
+
+    for key in ld_keys {
+        unsafe {
+            std::env::remove_var(key);
+        }
+    }
+}
+
+#[cfg(target_os = "macos")]
+pub(crate) fn pre_main_hardening_macos() {
+    // Prevent debuggers from attaching to this process.
+    let ret_code = unsafe { libc::ptrace(libc::PT_DENY_ATTACH, 0, std::ptr::null_mut(), 0) };
+    if ret_code == -1 {
+        eprintln!(
+            "ERROR: ptrace(PT_DENY_ATTACH) failed: {}",
+            std::io::Error::last_os_error()
+        );
+        std::process::exit(PTRACE_DENY_ATTACH_FAILED_EXIT_CODE);
+    }
+
+    // Set the core file size limit to 0 to prevent core dumps.
+    set_core_file_size_limit_to_zero();
+
+    // Remove all DYLD_ environment variables, which can be used to subvert
+    // library loading.
+    let dyld_keys: Vec<String> = std::env::vars()
+        .filter_map(|(key, _)| {
+            if key.starts_with("DYLD_") {
+                Some(key)
+            } else {
+                None
+            }
+        })
+        .collect();
+
+    for key in dyld_keys {
+        unsafe {
+            std::env::remove_var(key);
+        }
+    }
+}
+
+#[cfg(unix)]
+fn set_core_file_size_limit_to_zero() {
+    let rlim = libc::rlimit {
+        rlim_cur: 0,
+        rlim_max: 0,
+    };
+
+    let ret_code = unsafe { libc::setrlimit(libc::RLIMIT_CORE, &rlim) };
+    if ret_code != 0 {
+        eprintln!(
+            "ERROR: setrlimit(RLIMIT_CORE) failed: {}",
+            std::io::Error::last_os_error()
+        );
+        std::process::exit(SET_RLIMIT_CORE_FAILED_EXIT_CODE);
+    }
+}
+
+#[cfg(windows)]
+pub(crate) fn pre_main_hardening_windows() {
+    // TODO(mbolin): Perform the appropriate configuration for Windows.
+}