Chmod preserve root (#10033)

* chmod: Fix --preserve-root not being bypassed by path that resolves to root

* chmod: Regression tests for --preserve-root not being bypassed by path that resolves to root

src/uu/chmod/src/chmod.rs

@@ -407,7 +407,7 @@ impl Chmoder {
                 // should not change the permissions in this case
                 continue;
             }
-            if self.recursive && self.preserve_root && file == Path::new("/") {
+            if self.recursive && self.preserve_root && Self::is_root(file) {
                 return Err(ChmodError::PreserveRoot("/".into()).into());
             }
             if self.recursive {
@@ -419,6 +419,10 @@ impl Chmoder {
         r
     }
 
+    fn is_root(file: impl AsRef<Path>) -> bool {
+        matches!(fs::canonicalize(&file), Ok(p) if p == Path::new("/"))
+    }
+
     #[cfg(not(target_os = "linux"))]
     fn walk_dir_with_context(&self, file_path: &Path, is_command_line_arg: bool) -> UResult<()> {
         let mut r = self.chmod_file(file_path);

tests/by-util/test_chmod.rs

@@ -508,6 +508,17 @@ fn test_chmod_preserve_root() {
         .stderr_contains("chmod: it is dangerous to operate recursively on '/'");
 }
 
+#[test]
+fn test_chmod_preserve_root_with_paths_that_resolve_to_root() {
+    new_ucmd!()
+        .arg("-R")
+        .arg("--preserve-root")
+        .arg("755")
+        .arg("/../")
+        .fails_with_code(1)
+        .stderr_contains("chmod: it is dangerous to operate recursively on '/'");
+}
+
 #[test]
 fn test_chmod_symlink_non_existing_file() {
     let scene = TestScenario::new(util_name!());