archive: work from leaves up when unpacking direcories

src/archive.rs

@@ -222,7 +222,16 @@ impl Archive<dyn Read + '_> {
                 file.unpack_in(dst)?;
             }
         }
-        for mut dir in directories {
+
+        // Work from leaves up, with the assumption* that entries for
+        // parent directories preceed their children.  Otherwise when
+        // a parent directory has no write permission, any empty
+        // subdirectories beneath it cannot be created.
+        //
+        // [*] If sufficiently motivated, one can create an archive
+        // which violates this.  In practice, archives typically are
+        // structured this way.
+        for mut dir in directories.into_iter().rev() {
             dir.unpack_in(dst)?;
         }
 

tests/all.rs

@@ -1317,6 +1317,33 @@ fn read_only_directory_containing_files() {
     assert!(ar.unpack(td.path()).is_ok());
 }
 
+#[test]
+fn read_only_directory_containing_empty_directory() {
+    let td = t!(TempBuilder::new().prefix("tar-rs").tempdir());
+
+    let mut b = Builder::new(Vec::<u8>::new());
+
+    let mut h = Header::new_gnu();
+    t!(h.set_path("dir/"));
+    h.set_size(0);
+    h.set_entry_type(EntryType::dir());
+    h.set_mode(0o444);
+    h.set_cksum();
+    t!(b.append(&h, "".as_bytes()));
+
+    let mut h = Header::new_gnu();
+    t!(h.set_path("dir/subdir"));
+    h.set_size(0);
+    h.set_entry_type(EntryType::dir());
+    h.set_mode(0o755);
+    h.set_cksum();
+    t!(b.append(&h, "".as_bytes()));
+
+    let contents = t!(b.into_inner());
+    let mut ar = Archive::new(&contents[..]);
+    assert!(ar.unpack(td.path()).is_ok());
+}
+
 // This test was marked linux only due to macOS CI can't handle `set_current_dir` correctly
 #[test]
 #[cfg(target_os = "linux")]