fix: apply the superblock extension and cache image in every opener

File, MmapFile and LazyFile decoded the superblock extension and laid a
metadata cache image over the file's metadata; the other readers did
not, so the same file read differently by entry point: NativeVol,
AsyncHDF5File and MpiVol (clawhdf5-io) and the external source files of
a virtual dataset (clawhdf5-format vds.rs) read a file with an image
from its own bytes, which libhdf5 does not (they may be stale, or zeros:
h5clear_mdc_image.h5 failed with InvalidObjectHeaderVersion(0)), and
skipped the extension checks File::open makes (cve-2020-10810/10812).

Each of them owns its buffer, so each now calls the shared
superblock_ext::apply_cache_image_in_place, which checks the extension
and writes the image's entries in place (only the image block is
copied). These readers read whole datasets and cannot open a file and
fail each object, so an image libhdf5 cannot load is refused with the
image's error, never read around. clawhdf5-io's vol::load_hdf5 wraps it
for NativeVol (at open; for from_bytes the error is reported on read,
as a truncated file already was) and MpiVol. The MpiVol edit is minimal
and was not compiled: the mpi-io feature needs an MPI installation this
machine does not have (mpi-sys's build script panics).

Tests: NativeVol (open_path and from_bytes), AsyncHDF5File and a VDS
whose source file is h5clear_mdc_image.h5 (vds_interop.rs, against
h5py) read the fixture's values; the corrupted-image variants are
refused. Each fails without its fix.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

crates/clawhdf5-format/src/vds.rs

@@ -803,7 +803,11 @@ impl<'a, 'r> Sources<'a, 'r> {
             let resolver = self.resolver.ok_or_else(|| {
                 vds_err("external-file virtual dataset sources require a file resolver")
             })?;
-            self.cached_file = Some((String::from(name), resolver(name)?));
+            let mut bytes = resolver(name)?;
+            if let Some(b) = bytes.as_mut() {
+                load_source_file(b)?;
+            }
+            self.cached_file = Some((String::from(name), bytes));
         }
         // An external file is handed over whole; its addresses are relative
         // to its superblock, so skip any user block.
@@ -851,6 +855,23 @@ impl<'a, 'r> Sources<'a, 'r> {
     }
 }
 
+/// Check an external source file's superblock extension as libhdf5 does
+/// when it opens the file, and write any metadata cache image over its
+/// metadata in place: libhdf5 reads the image's entries instead of the
+/// file's own, possibly stale, bytes (`crate::superblock_ext`). A source
+/// file whose image cannot be loaded is an error, as other corrupt source
+/// files are here.
+fn load_source_file(whole: &mut [u8]) -> Result<(), FormatError> {
+    let base = crate::signature::find_signature(whole)?;
+    let sb = crate::superblock::Superblock::parse(&whole[base..], 0)?;
+    // The end of file the superblock records; a truncated source file is
+    // read as before, up to its length.
+    let end = sb
+        .data_end(base as u64, whole.len() as u64)
+        .map_or(whole.len(), |e| base + e as usize);
+    crate::superblock_ext::apply_cache_image_in_place(&mut whole[base..end], &sb)
+}
+
 /// Whether elements of `dt` contain addresses into their own file:
 /// variable-length data (global-heap IDs) or references.
 fn holds_file_addresses(dt: &Datatype) -> bool {

crates/clawhdf5-io/src/async_read.rs

@@ -288,6 +288,12 @@ impl AsyncHDF5File {
         // superblock records, as libhdf5 does.
         let end = superblock.data_end(user_block as u64, whole_len)?;
         data.truncate(end as usize);
+        // Check the superblock extension as libhdf5 does at open, and write
+        // any metadata cache image over the file's metadata (libhdf5 reads
+        // the image's entries instead of the file's own, possibly stale,
+        // bytes). An image libhdf5 cannot load is refused: this reader has
+        // no way to open the file and fail each object instead.
+        clawhdf5_format::superblock_ext::apply_cache_image_in_place(&mut data, &superblock)?;
         Ok(Self { data, superblock })
     }
 
@@ -430,6 +436,41 @@ mod tests {
         fw.finish().unwrap()
     }
 
+    /// libhdf5's `h5clear_mdc_image.h5` (see the clawhdf5 crate's
+    /// `tests/metadata_cache_image.rs`): the root group's header exists
+    /// only in the file's metadata cache image.
+    fn cache_image_fixture() -> Vec<u8> {
+        std::fs::read(concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/../clawhdf5/tests/fixtures/h5clear_mdc_image.h5"
+        ))
+        .unwrap()
+    }
+
+    #[tokio::test]
+    async fn reads_through_a_metadata_cache_image() {
+        let bytes = cache_image_fixture();
+        let file = AsyncHDF5File::from_bytes(bytes.clone()).unwrap();
+        let info = file.read_dataset_raw("DSET").await.unwrap();
+        assert_eq!(info.shape, [50, 100]);
+        let values: Vec<i32> = info
+            .raw
+            .chunks_exact(4)
+            .map(|b| i32::from_le_bytes(b.try_into().unwrap()))
+            .collect();
+        let expected: Vec<i32> = (0..50).flat_map(|i| (0..100).map(move |j| i * j)).collect();
+        assert_eq!(values, expected);
+
+        // An image libhdf5 cannot load is refused at open.
+        let mut bad = bytes;
+        let at = bad.windows(4).position(|w| w == b"MDCI").unwrap();
+        bad[at] = b'X';
+        assert!(matches!(
+            AsyncHDF5File::from_bytes(bad),
+            Err(AsyncHDF5Error::Format(FormatError::InvalidCacheImage(_)))
+        ));
+    }
+
     // --- AsyncMemoryReader tests ---
 
     #[tokio::test]

crates/clawhdf5-io/src/mpi_vol.rs

@@ -191,7 +191,10 @@ fn mpi_collective_read(vol: &MpiVol, location: &str, path: &str) -> Result<Vec<u
     let mut len_buf = [0usize; 1];
 
     if rank == 0 {
-        let file = std::fs::read(location).map_err(VolError::Io)?;
+        let mut file = std::fs::read(location).map_err(VolError::Io)?;
+        // Checked as libhdf5 checks a file at open, with any metadata cache
+        // image written over the metadata (see `vol::load_hdf5`).
+        crate::vol::load_hdf5(&mut file)?;
         // From the superblock to the recorded end of file; truncated files
         // are refused.
         let (bytes, sb) = crate::vol::hdf5_view(&file)?;

crates/clawhdf5-io/src/vol.rs

@@ -208,6 +208,9 @@ pub trait VirtualObjectLayer: Send + Sync {
 pub struct NativeVol {
     data: Option<Vec<u8>>,
     location: Option<String>,
+    /// Why the bytes given to [`NativeVol::from_bytes`] cannot be read
+    /// (what `open` would have refused them for).
+    load_error: Option<String>,
 }
 
 /// The HDF5 bytes of a whole file and its superblock: from the superblock
@@ -228,12 +231,35 @@ pub(crate) fn hdf5_view(
     Ok((&data[..end as usize], sb))
 }
 
+/// Check a whole file as libhdf5 does when it opens it ([`hdf5_view`], and
+/// the superblock extension), and write any metadata cache image over the
+/// file's metadata in place: libhdf5 reads the image's entries instead of
+/// the file's own bytes at their addresses, which may be stale
+/// (`clawhdf5_format::superblock_ext`). A file whose image libhdf5 cannot
+/// load is refused: a connector that reads whole datasets has no way to
+/// open the file and fail each object instead.
+pub(crate) fn load_hdf5(whole: &mut [u8]) -> Result<(), VolError> {
+    use clawhdf5_format::superblock_ext::apply_cache_image_in_place;
+    let err = |e: clawhdf5_format::error::FormatError| VolError::DataError(e.to_string());
+    let (len, sb) = {
+        let (data, sb) = hdf5_view(whole)?;
+        (data.len(), sb)
+    };
+    // hdf5_view's bytes start at the superblock, after any user block.
+    let base = clawhdf5_format::signature::split_user_block(whole)
+        .map_err(err)?
+        .0
+        .len();
+    apply_cache_image_in_place(&mut whole[base..base + len], &sb).map_err(err)
+}
+
 impl NativeVol {
     /// Create a new native VOL connector.
     pub fn new() -> Self {
         Self {
             data: None,
             location: None,
+            load_error: None,
         }
     }
 
@@ -245,10 +271,12 @@ impl NativeVol {
     }
 
     /// Create a native VOL connector from bytes already in memory.
-    pub fn from_bytes(data: Vec<u8>) -> Self {
+    pub fn from_bytes(mut data: Vec<u8>) -> Self {
+        let load_error = load_hdf5(&mut data).err().map(|e| e.to_string());
         Self {
             data: Some(data),
             location: Some("<memory>".into()),
+            load_error,
         }
     }
 
@@ -281,10 +309,12 @@ impl VirtualObjectLayer for NativeVol {
     }
 
     fn open(&mut self, location: &str) -> Result<(), VolError> {
-        let data = std::fs::read(location)?;
-        // Refuse a truncated file at open, as libhdf5 does.
-        hdf5_view(&data)?;
+        let mut data = std::fs::read(location)?;
+        // Refuse a truncated file at open, as libhdf5 does, and load any
+        // metadata cache image.
+        load_hdf5(&mut data)?;
         self.data = Some(data);
+        self.load_error = None;
         self.location = Some(location.to_string());
         Ok(())
     }
@@ -299,6 +329,9 @@ impl VirtualObjectLayer for NativeVol {
         let data = self.data.as_ref().ok_or_else(|| {
             VolError::Io(io::Error::new(io::ErrorKind::NotConnected, "file not open"))
         })?;
+        if let Some(e) = &self.load_error {
+            return Err(VolError::DataError(e.clone()));
+        }
 
         use clawhdf5_format::{
             data_layout::DataLayout, data_read::read_raw_data_full, dataspace::Dataspace,
@@ -434,6 +467,43 @@ mod tests {
         assert_eq!(raw.len(), 24);
     }
 
+    /// libhdf5's `h5clear_mdc_image.h5` (see the clawhdf5 crate's
+    /// `tests/metadata_cache_image.rs`): the root group's header exists
+    /// only in the file's metadata cache image, so reading the file's own
+    /// bytes finds zeros there.
+    #[test]
+    fn native_vol_reads_through_a_metadata_cache_image() {
+        let path = concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/../clawhdf5/tests/fixtures/h5clear_mdc_image.h5"
+        );
+        let expected: Vec<u8> = (0..50)
+            .flat_map(|i| (0..100).map(move |j| i * j))
+            .flat_map(i32::to_le_bytes)
+            .collect();
+        let vol = NativeVol::open_path(path).unwrap();
+        assert_eq!(vol.read_dataset("DSET").unwrap(), expected);
+        let bytes = std::fs::read(path).unwrap();
+        let vol = NativeVol::from_bytes(bytes.clone());
+        assert_eq!(vol.read_dataset("DSET").unwrap(), expected);
+
+        // An image libhdf5 cannot load is refused, not read around.
+        let mut bad = bytes;
+        let at = bad.windows(4).position(|w| w == b"MDCI").unwrap();
+        bad[at] = b'X';
+        let err = NativeVol::from_bytes(bad.clone())
+            .read_dataset("DSET")
+            .unwrap_err();
+        assert!(err.to_string().contains("cache image"), "{err}");
+        let dir = tempfile::tempdir().unwrap();
+        let bad_path = dir.path().join("bad_image.h5");
+        std::fs::write(&bad_path, &bad).unwrap();
+        let err = NativeVol::open_path(bad_path.to_str().unwrap())
+            .err()
+            .unwrap();
+        assert!(err.to_string().contains("cache image"), "{err}");
+    }
+
     #[test]
     fn vol_error_display() {
         let err = VolError::Unsupported("read_dataset".into());

crates/clawhdf5/tests/vds_interop.rs

@@ -486,3 +486,26 @@ fn vds_libhdf5_test_files() {
         vec![5, 10, 10]
     );
 }
+
+/// A source file with a metadata cache image (libhdf5's
+/// `h5clear_mdc_image.h5`, whose root group's header exists only in the
+/// image) is read through the image, as libhdf5 opens it. Source files were
+/// read from their own bytes, and this one failed on the root group.
+#[test]
+fn vds_source_file_with_a_metadata_cache_image() {
+    skip_if_no_python!();
+    let dir = tempfile::tempdir().unwrap();
+    let fixture = Path::new(env!("CARGO_MANIFEST_DIR")).join("tests/fixtures/h5clear_mdc_image.h5");
+    std::fs::copy(&fixture, dir.path().join("src.h5")).unwrap();
+    generate(
+        dir.path(),
+        r#"
+with h5py.File("vds.h5", "w", libver="latest") as f:
+    lay = h5py.VirtualLayout(shape=(3, 100), dtype="i4")
+    lay[0:3, :] = h5py.VirtualSource("src.h5", "DSET", shape=(50, 100))[5:8, :]
+    f.create_virtual_dataset("v", lay)
+expect("vds.h5", "v", "image_source")
+"#,
+    );
+    assert_matches_libhdf5(dir.path(), "vds.h5", "v", "image_source");
+}