fix: Could still select a fake CDE over a real one in some cases

src/read.rs

@@ -69,6 +69,7 @@ pub(crate) mod zip_archive {
         pub(crate) files: Vec<super::ZipFileData>,
         pub(super) offset: u64,
         pub(super) dir_start: u64,
+        pub(super) dir_end: u64,
         // This isn't yet used anywhere, but it is here for use cases in the future.
         #[allow(dead_code)]
         pub(super) config: super::Config,
@@ -721,7 +722,7 @@ impl<R: Read + Seek> ZipArchive<R> {
         }
         let (footer, shared) = ok_results
             .into_iter()
-            .max_by_key(|(_, shared)| (shared.dir_start - shared.offset, shared.dir_start))
+            .max_by_key(|(_, shared)| (shared.dir_end, u64::MAX - shared.dir_start))
             .unwrap();
         reader.seek(io::SeekFrom::Start(shared.dir_start))?;
         Ok((Rc::try_unwrap(footer).unwrap(), shared.build()))
@@ -748,10 +749,12 @@ impl<R: Read + Seek> ZipArchive<R> {
             let file = central_header_to_zip_file(reader, dir_info.archive_offset)?;
             files.push(file);
         }
+        let dir_end = reader.stream_position()?;
         Ok(SharedBuilder {
             files,
             offset: dir_info.archive_offset,
             dir_start: dir_info.directory_start,
+            dir_end,
             config,
         })
     }
@@ -820,6 +823,7 @@ impl<R: Read + Seek> ZipArchive<R> {
     ///
     /// This uses the central directory record of the ZIP file, and ignores local file headers.
     pub fn with_config(config: Config, mut reader: R) -> ZipResult<ZipArchive<R>> {
+        reader.seek(SeekFrom::Start(0))?;
         if let Ok((footer, shared)) = Self::get_metadata(config, &mut reader) {
             return Ok(ZipArchive {
                 reader,

src/write.rs

@@ -625,6 +625,7 @@ impl<A: Read + Write + Seek> ZipWriter<A> {
     ///
     /// This uses the given read configuration to initially read the archive.
     pub fn new_append_with_config(config: Config, mut readwriter: A) -> ZipResult<ZipWriter<A>> {
+        readwriter.seek(SeekFrom::Start(0))?;
         if let Ok((footer, shared)) = ZipArchive::get_metadata(config, &mut readwriter) {
             Ok(ZipWriter {
                 inner: Storer(MaybeEncrypted::Unencrypted(readwriter)),
@@ -3368,4 +3369,46 @@ mod test {
         let _ = writer.finish_into_readable()?;
         Ok(())
     }
+
+    #[cfg(all(feature = "bzip2", feature = "aes-crypto"))]
+    #[test]
+    fn test_fuzz_crash_2024_06_18b() -> ZipResult<()> {
+        let mut writer = ZipWriter::new(Cursor::new(Vec::new()));
+        writer.set_flush_on_finish_file(true);
+        writer.set_raw_comment([0].into());
+        writer = ZipWriter::new_append(writer.finish_into_readable()?.into_inner())?;
+        assert_eq!(writer.get_raw_comment()[0], 0);
+        let options = FileOptions {
+            compression_method: CompressionMethod::Bzip2,
+            compression_level: None,
+            last_modified_time: DateTime::from_date_and_time(2009, 6, 3, 13, 37, 39)?,
+            permissions: Some(2644352413),
+            large_file: true,
+            encrypt_with: Some(crate::write::EncryptWith::Aes {
+                mode: crate::AesMode::Aes256,
+                password: "",
+            }),
+            extended_options: ExtendedFileOptions {
+                extra_data: vec![].into(),
+                central_extra_data: vec![].into(),
+            },
+            alignment: 255,
+            ..Default::default()
+        };
+        writer.add_symlink_from_path("", "", options)?;
+        writer.deep_copy_file_from_path("", "PK\u{5}\u{6}\0\0\0\0\0\0\0\0\0\0\0\0\0\u{4}\0\0\0")?;
+        writer = ZipWriter::new_append(writer.finish_into_readable()?.into_inner())?;
+        assert_eq!(writer.get_raw_comment()[0], 0);
+        writer.deep_copy_file_from_path(
+            "PK\u{5}\u{6}\0\0\0\0\0\0\0\0\0\0\0\0\0\u{4}\0\0\0",
+            "\u{2}yy\u{5}qu\0",
+        )?;
+        let finished = writer.finish()?;
+        let archive = ZipArchive::new(finished.clone())?;
+        assert_eq!(archive.comment(), [0]);
+        writer = ZipWriter::new_append(finished)?;
+        assert_eq!(writer.get_raw_comment()[0], 0);
+        let _ = writer.finish_into_readable()?;
+        Ok(())
+    }
 }