nohup: create nohup.out with mode 0o600 regardless of umask

Cargo.lock

@@ -3603,6 +3603,7 @@ dependencies = [
  "clap",
  "fluent",
  "libc",
+ "nix",
  "thiserror 2.0.17",
  "uucore",
 ]

src/uu/nohup/Cargo.toml

@@ -20,6 +20,7 @@ path = "src/nohup.rs"
 [dependencies]
 clap = { workspace = true }
 libc = { workspace = true }
+nix = { workspace = true, features = ["fs"] }
 uucore = { workspace = true, features = ["fs"] }
 thiserror = { workspace = true }
 fluent = { workspace = true }

src/uu/nohup/src/nohup.rs

@@ -7,9 +7,11 @@
 
 use clap::{Arg, ArgAction, Command};
 use libc::{SIG_IGN, SIGHUP, dup2, signal};
+use nix::sys::stat::{Mode, umask};
 use std::env;
 use std::fs::{File, OpenOptions};
 use std::io::{Error, ErrorKind, IsTerminal};
+use std::os::unix::fs::OpenOptionsExt;
 use std::os::unix::prelude::*;
 use std::os::unix::process::CommandExt;
 use std::path::{Path, PathBuf};
@@ -123,17 +125,31 @@ fn replace_fds() -> UResult<()> {
     Ok(())
 }
 
+/// Open nohup.out file with mode 0o600, temporarily clearing umask.
+/// The umask is cleared to ensure the file is created with exactly 0o600 permissions.
+fn open_nohup_file(path: &Path) -> std::io::Result<File> {
+    // Clear umask (set it to 0) and save the old value
+    let old_umask = umask(Mode::from_bits_truncate(0));
+
+    let result = OpenOptions::new()
+        .create(true)
+        .append(true)
+        .mode(0o600)
+        .open(path);
+
+    // Restore previous umask
+    umask(old_umask);
+
+    result
+}
+
 fn find_stdout() -> UResult<File> {
     let internal_failure_code = match env::var("POSIXLY_CORRECT") {
         Ok(_) => POSIX_NOHUP_FAILURE,
         Err(_) => EXIT_CANCELED,
     };
 
-    match OpenOptions::new()
-        .create(true)
-        .append(true)
-        .open(Path::new(NOHUP_OUT))
-    {
+    match open_nohup_file(Path::new(NOHUP_OUT)) {
         Ok(t) => {
             show_error!(
                 "{}",
@@ -148,7 +164,7 @@ fn find_stdout() -> UResult<File> {
             let mut homeout = PathBuf::from(home);
             homeout.push(NOHUP_OUT);
             let homeout_str = homeout.to_str().unwrap();
-            match OpenOptions::new().create(true).append(true).open(&homeout) {
+            match open_nohup_file(&homeout) {
                 Ok(t) => {
                     show_error!(
                         "{}",

tests/by-util/test_nohup.rs

@@ -3,9 +3,11 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 // spell-checker:ignore winsize Openpty openpty xpixel ypixel ptyprocess
+use std::os::unix::fs::PermissionsExt;
 use std::thread::sleep;
 use uutests::at_and_ucmd;
 use uutests::new_ucmd;
+use uutests::util::TerminalSimulation;
 use uutests::util::TestScenario;
 use uutests::util_name;
 
@@ -238,3 +240,28 @@ fn test_nohup_stderr_to_stdout() {
     assert!(content.contains("stdout message"));
     assert!(content.contains("stderr message"));
 }
+
+#[test]
+fn test_nohup_file_permissions_ignore_umask_always_o600() {
+    for umask_val in [0o077, 0o000] {
+        let ts = TestScenario::new(util_name!());
+        ts.ucmd()
+            .terminal_sim_stdio(TerminalSimulation {
+                stdin: true,
+                stdout: true,
+                stderr: true,
+                size: None,
+            })
+            .umask(umask_val)
+            .args(&["echo", "test"])
+            .succeeds();
+
+        sleep(std::time::Duration::from_millis(10));
+        let mode = std::fs::metadata(ts.fixtures.plus_as_string("nohup.out"))
+            .unwrap()
+            .permissions()
+            .mode()
+            & 0o777;
+        assert_eq!(mode, 0o600, "with umask {umask_val:o}, got mode {mode:o}");
+    }
+}