From 0e29cca8954d054c4b26e8bcbe54e3c590eab44b Mon Sep 17 00:00:00 2001
From: burak yorulmaz <iburaky@gmail.com>
Date: Mon, 22 Dec 2025 18:03:17 +0100
Subject: [PATCH] cp: strip setuid & setgid when preserving ownership or group
 fails

---
 src/uu/cp/src/cp.rs      | 18 +++++++-
 tests/by-util/test_cp.rs | 95 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 112 insertions(+), 1 deletion(-)

diff --git a/src/uu/cp/src/cp.rs b/src/uu/cp/src/cp.rs
index c1df9ed139a..f06748b482c 100644
--- a/src/uu/cp/src/cp.rs
+++ b/src/uu/cp/src/cp.rs
@@ -1708,7 +1708,23 @@ pub(crate) fn copy_attributes(
         // do nothing, since every symbolic link has the same
         // permissions.
         if !dest.is_symlink() {
-            fs::set_permissions(dest, source_metadata.permissions())
+            // gnu compatibility: cp strips both setuid & setgid bits if preserving either ownership or group fails
+            let mut perms = source_metadata.permissions();
+            #[cfg(unix)]
+            {
+                use std::os::unix::fs::MetadataExt;
+
+                let dest_metadata = fs::symlink_metadata(dest)
+                    .map_err(|e| CpError::IoErrContext(e, context.to_owned()))?;
+
+                if dest_metadata.uid() != source_metadata.uid()
+                    || dest_metadata.gid() != source_metadata.gid()
+                {
+                    let mode = perms.mode() & !0o6000;
+                    perms.set_mode(mode);
+                }
+            }
+            fs::set_permissions(dest, perms)
                 .map_err(|e| CpError::IoErrContext(e, context.to_owned()))?;
             // FIXME: Implement this for windows as well
             #[cfg(feature = "feat_acl")]
diff --git a/tests/by-util/test_cp.rs b/tests/by-util/test_cp.rs
index 2563e533ae4..04a9799b6a9 100644
--- a/tests/by-util/test_cp.rs
+++ b/tests/by-util/test_cp.rs
@@ -7400,3 +7400,98 @@ fn test_cp_recurse_verbose_output_with_symlink_already_exists() {
         .no_stderr()
         .stdout_is(output);
 }
+
+#[test]
+#[cfg(unix)]
+fn test_cp_strip_uid_gid_preserve_ownership_fails() {
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+    let ucmd = &mut scene.ucmd();
+
+    let src = "src";
+    let dest_dir = "dir";
+    let dest = "dir/dest";
+
+    // Test must be run as root (or with `sudo -E`)
+    if scene.cmd("whoami").run().stdout_str() != "root\n" {
+        return;
+    }
+
+    at.touch(src);
+    at.set_mode(src, 0o6755);
+
+    at.mkdir(dest_dir);
+    at.set_mode(dest_dir, 0o777);
+
+    // Need to drop privileges for preserving ownership to fail
+    unsafe {
+        libc::seteuid(1000);
+    }
+
+    ucmd.arg("-p").arg(src).arg(dest).succeeds();
+
+    // When preserving ownership fails, setuid and setgid bits should be stripped
+    let dest_metadata = at.metadata(dest);
+    assert_eq!(
+        dest_metadata.mode() & 0o6755,
+        0o755,
+        "setuid or setgid not stripped"
+    );
+}
+
+#[test]
+#[cfg(unix)]
+fn test_cp_strip_uid_gid_preserve_group_fails() {
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+    let ucmd = &mut scene.ucmd();
+
+    let dir = "dir";
+    let src = "dir/src";
+    let dest = "dir/dest";
+
+    // Test must be run as root (or with `sudo -E`)
+    if scene.cmd("whoami").run().stdout_str() != "root\n" {
+        return;
+    }
+
+    at.mkdir(dir);
+    at.set_mode(dir, 0o777);
+
+    // Drop privileges before creating file
+    // Will need root to set group later
+    let orig_euid = unsafe { libc::geteuid() };
+    let orig_egid = unsafe { libc::getegid() };
+
+    unsafe {
+        libc::seteuid(1000);
+        libc::setegid(1000);
+    }
+
+    at.touch(src);
+    at.set_mode(src, 0o6755);
+
+    // Escalate privileges to set group
+    unsafe {
+        libc::seteuid(orig_euid);
+        libc::setegid(orig_egid);
+    }
+
+    scene.cmd("chgrp").arg("0").arg(src).succeeds();
+
+    // Drop again before running cp
+    unsafe {
+        libc::seteuid(1000);
+        libc::setegid(1000);
+    }
+
+    ucmd.arg("-p").arg(src).arg(dest).succeeds();
+
+    // When preserving group fails, setuid and setgid bits should be stripped
+    let dest_metadata = at.metadata(dest);
+    assert_eq!(
+        dest_metadata.mode() & 0o6755,
+        0o755,
+        "setuid or setgid not stripped"
+    );
+}