find: -ls: don't panic on an unmapped owner uid/gid

`find <file> -ls` panicked (exit 101) when the file's owning uid (or gid) had
no `/etc/passwd` (`/etc/group`) entry: it resolved the name with
`User::from_uid(...).unwrap().unwrap()`, and the inner unwrap aborts on the
`Ok(None)` that an unmapped id returns. Unmapped owners are routine (extracted
archives, NFS, deleted accounts, container images).

Resolve the uid/gid via `uucore::entries::uid2usr`/`gid2grp`, falling back to
the numeric id when there is no entry, matching GNU find (which prints the
number). These helpers already serialize the non-thread-safe getpwuid/getgrgid
behind a mutex, so reuse them rather than reimplementing the lookup.

Add a -ls integration test that chowns a file to an unmapped id and checks the
numeric fallback; it skips when the process lacks the privilege to do so.

src/find/matchers/ls.rs

@@ -126,7 +126,6 @@ impl Ls {
         mut out: impl Write,
         print_error_message: bool,
     ) {
-        use nix::unistd::{Gid, Group, Uid, User};
         use std::os::unix::fs::{MetadataExt, PermissionsExt};
 
         let metadata = file_info.metadata().unwrap();
@@ -150,14 +149,13 @@ impl Ls {
         let permission =
             { format_permissions(metadata.permissions().mode() as uucore::libc::mode_t) };
         let hard_links = metadata.nlink();
-        let user = {
-            let uid = metadata.uid();
-            User::from_uid(Uid::from_raw(uid)).unwrap().unwrap().name
-        };
-        let group = {
-            let gid = metadata.gid();
-            Group::from_gid(Gid::from_raw(gid)).unwrap().unwrap().name
-        };
+        // Fall back to the numeric id when the uid/gid has no passwd/group entry
+        // (unmapped owner) — matching GNU find, which never crashes. uucore::entries
+        // serializes the non-thread-safe getpwuid/getgrgid behind a mutex.
+        let user =
+            uucore::entries::uid2usr(metadata.uid()).unwrap_or_else(|_| metadata.uid().to_string());
+        let group =
+            uucore::entries::gid2grp(metadata.gid()).unwrap_or_else(|_| metadata.gid().to_string());
         let size = metadata.size();
         let last_modified = {
             let system_time = metadata.modified().unwrap();

tests/test_find.rs

@@ -1018,6 +1018,37 @@ fn find_ls() {
         .no_stderr();
 }
 
+// Regression test for uutils/findutils#717: `-ls` used to abort (exit 101) when
+// a file's owning uid/gid had no passwd/group entry; it must fall back to the
+// numeric id like GNU find. Creating such a file needs privilege to chown to an
+// unmapped id, so skip when that isn't available (e.g. non-root CI).
+#[test]
+#[cfg(unix)]
+fn find_ls_unmapped_owner_renders_numeric_id() {
+    use nix::unistd::{chown, Gid, Uid};
+
+    let temp_dir = Builder::new().prefix("find_ls_unmapped").tempdir().unwrap();
+    let file = temp_dir.path().join("orphan");
+    File::create(&file).unwrap();
+
+    // A uid/gid essentially never present in /etc/passwd or /etc/group.
+    let unmapped = 4_000_000_000u32;
+    if chown(
+        &file,
+        Some(Uid::from_raw(unmapped)),
+        Some(Gid::from_raw(unmapped)),
+    )
+    .is_err()
+    {
+        return;
+    }
+
+    ucmd()
+        .args(&[file.to_str().unwrap(), "-ls"])
+        .succeeds()
+        .stdout_contains(unmapped.to_string());
+}
+
 #[test]
 #[cfg(unix)]
 fn find_slashes() {