timeout: add parent-death guard for monitored command

src/uu/timeout/locales/en-US.ftl

@@ -22,6 +22,7 @@ timeout-after-help = Upon timeout, send the TERM signal to COMMAND, if no other
 # Error messages
 timeout-error-invalid-signal = { $signal }: invalid signal
 timeout-error-failed-to-execute-process = failed to execute process: { $error }
+timeout-error-monitor-exited-before-child-exec = timeout monitor exited before child exec
 
 # Verbose messages
 timeout-verbose-sending-signal = sending signal { $signal } to command { $command }

src/uu/timeout/locales/fr-FR.ftl

@@ -22,6 +22,7 @@ timeout-after-help = À l'expiration du délai, le signal TERM est envoyé à CO
 # Messages d'erreur
 timeout-error-invalid-signal = { $signal } : signal invalide
 timeout-error-failed-to-execute-process = échec d'exécution du processus : { $error }
+timeout-error-monitor-exited-before-child-exec = le processus de délai s'est terminé avant l'exécution du processus enfant
 
 # Messages détaillés
 timeout-verbose-sending-signal = envoi du signal { $signal } à la commande { $command }

src/uu/timeout/src/timeout.rs

@@ -3,13 +3,13 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 
-// spell-checker:ignore (ToDO) tstr sigstr cmdname setpgid sigchld getpid
+// spell-checker:ignore (ToDO) tstr sigstr cmdname setpgid sigchld getpid getppid
 
 mod status;
 
 use crate::status::ExitStatus;
 use clap::{Arg, ArgAction, Command};
-use std::io::{ErrorKind, Write};
+use std::io::{Error, ErrorKind, Write};
 use std::os::unix::process::ExitStatusExt;
 use std::process::{self, Child, Stdio};
 use std::sync::atomic::{self, AtomicBool};
@@ -26,7 +26,7 @@ use uucore::{
 };
 
 use nix::sys::signal::{SigHandler, Signal, kill};
-use nix::unistd::{Pid, getpid, setpgid};
+use nix::unistd::{Pid, getpid, getppid, setpgid};
 #[cfg(unix)]
 use std::os::unix::process::CommandExt;
 
@@ -380,6 +380,13 @@ fn timeout(
                 if let Some(sig) = death_sig {
                     let _ = nix::sys::prctl::set_pdeathsig(sig);
                 }
+                // Close the post-fork race where the timeout monitor can die
+                // after PDEATHSIG setup but before exec starts the target command.
+                if getppid().as_raw() == 1 {
+                    return Err(Error::other(
+                        translate!("timeout-error-monitor-exited-before-child-exec"),
+                    ));
+                }
                 Ok(())
             });
         }