pidof: match processes by executable and by rewritten titles

src/uu/pidof/src/pidof.rs

@@ -3,6 +3,7 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 
+use std::fs;
 use std::path::PathBuf;
 
 use clap::{crate_version, Arg, ArgAction, ArgMatches, Command};
@@ -50,8 +51,16 @@ fn match_process_name(
     with_workers: bool,
     match_scripts: bool,
 ) -> bool {
-    let binding = process.cmdline.split(' ').collect::<Vec<_>>();
-    let path = binding.first().unwrap().to_string();
+    // `cmdline` has the arguments joined with spaces, so read them again to
+    // get argv[0] as it is.
+    let Ok(raw) = fs::read(format!("/proc/{}/cmdline", process.pid)) else {
+        return false;
+    };
+    let binding = raw
+        .split(|&b| b == 0)
+        .map(String::from_utf8_lossy)
+        .collect::<Vec<_>>();
+    let path = binding.first().map(|it| it.to_string()).unwrap_or_default();
 
     if path.is_empty() {
         if !with_workers {
@@ -60,15 +69,32 @@ fn match_process_name(
         return process.name().unwrap() == name_to_match;
     };
 
-    if PathBuf::from(path).file_name().unwrap().to_str().unwrap() == name_to_match {
+    if PathBuf::from(&path).file_name().and_then(|f| f.to_str()) == Some(name_to_match) {
+        return true;
+    }
+
+    // Like procps-ng, also match the executable, so a process started with
+    // another argv[0] (`exec -a`) is still found, also by the 15-byte name
+    // the kernel cuts it to.
+    if let Ok(exe) = fs::read_link(format!("/proc/{}/exe", process.pid)) {
+        if let Some(exe) = exe.file_name().and_then(|f| f.to_str()) {
+            if exe == name_to_match || exe.as_bytes().get(..15) == Some(name_to_match.as_bytes()) {
+                return true;
+            }
+        }
+    }
+
+    // A process that rewrites its title, like "sshd: /usr/sbin/sshd -D", is
+    // matched by its process name too.
+    if path.contains(' ') && process.name().unwrap() == name_to_match {
         return true;
     }
 
     // When a script (ie. file starting with e.g. #!/bin/sh) is run like `./script.sh`, then
     // its cmdline will look like `/bin/sh ./script.sh` but its .name() will be `script.sh`.
     // As name() gets truncated to 15 characters, the original pidof seems to always do a prefix match.
     if match_scripts && binding.len() > 1 {
-        return PathBuf::from(binding[1])
+        return PathBuf::from(binding[1].as_ref())
             .file_name()
             .map(|f| f.to_str().unwrap())
             .is_some_and(|f| f == name_to_match && f.starts_with(&process.name().unwrap()));

tests/by-util/test_pidof.rs

@@ -158,3 +158,46 @@ fn test_script() {
     executed_via_sh_child.kill().unwrap();
     executed_via_sh_child.wait().unwrap();
 }
+
+#[test]
+#[cfg(target_os = "linux")]
+fn test_process_with_another_argv0() {
+    use std::os::unix::process::CommandExt;
+
+    // A copy of the shell under its own name, so the executable and the
+    // process name are known.
+    let temp_dir = tempfile::tempdir().unwrap();
+    let program = temp_dir.path().join("pidoftitletest");
+    std::fs::copy("/bin/sh", &program).unwrap();
+
+    for argv0 in ["pidoftitletest: worker process", "another-argv0"] {
+        // "; :" keeps the shell from replacing itself with sleep. Other tests
+        // forking while the copy was open for writing make exec fail with
+        // ETXTBSY for a moment, so retry that.
+        let mut child = (0..100)
+            .find_map(|_| {
+                match std::process::Command::new(&program)
+                    .arg0(argv0)
+                    .args(["-c", "sleep 5; :"])
+                    .spawn()
+                {
+                    Err(e) if e.kind() == std::io::ErrorKind::ExecutableFileBusy => {
+                        std::thread::sleep(std::time::Duration::from_millis(10));
+                        None
+                    }
+                    result => Some(result.unwrap()),
+                }
+            })
+            .unwrap();
+        std::thread::sleep(std::time::Duration::from_millis(200));
+
+        new_ucmd!()
+            .arg("pidoftitletest")
+            .succeeds()
+            .stdout_contains(child.id().to_string());
+        new_ucmd!().arg("pidoftitletest:").fails();
+
+        child.kill().unwrap();
+        child.wait().unwrap();
+    }
+}