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format: bound Storage reads that hostile size fields could stretch

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On a backend without the file in memory, a structure read whose length
comes from untrusted header fields was clamped only by the end of the
file, so a crafted size made one read (and copy) of up to the rest of
the file. Each such read now covers what the parser actually uses:

- local heap names: read in growing pieces (64 bytes first, then 4x)
  up to the end of the data segment, instead of the rest of the segment
  per name (quadratic for a big symbol-table group);
- fractal heap indirect blocks: the doubling-table geometry locates the
  entry covering the object, and the first read ends at that entry; only
  if it is unallocated does the walk read the rest of the block (it
  visits every entry then). One walk implementation serves both;
- paged fixed/extensible array data blocks over 1 MiB: the prefix and
  page bitmap, then each page in use on its own (smaller blocks are
  still one read);
- blocks under one checksum (non-paged array data blocks, extensible
  array index and super blocks): the bounds check that comes first (the
  checksum's; the page bitmap's for a super block) is made against the
  file length before reading (Window::check_extent), so a block claimed
  past the end of the file costs no read. With the checksum feature off
  the parser has no such first check and the old read stands.

Other windows were already bounded (the superblock and object header
prefixes, the fractal heap header by a u16, SOHM tables by u8/u16
counts) or are exact reads checked against the file length first.
In memory nothing changes: the pieces are borrowed slices.

Tests: CountingStorage over a crafted heap (16 MiB file, width and rows
0xFFFF: under 1 KiB read, 16.7 MB before), a heap segment claiming 64 MiB
(one 64-byte read per short name), long names at every piece boundary,
a fixed array block claimed past the end of a 16 MiB file (under 64
bytes read), and in the equivalence harness an h5py file with a 2.4 MB
fixed array block and a >1 MiB extensible array block, whole and cut at
97 points: every chunk index agrees with the slice read and the largest
takes 205 KB (2.4 MB and 1.2 MB when read whole).

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
This commit is contained in:
osobh
2026-09-26 14:31:46 -05:00
co-authored by Claude Opus 5.5
parent e5359354b7
commit 76c97f6c94
6 changed files with 467 additions and 95 deletions
Download Patch File Download Diff File Expand all files Collapse all files
crates/clawhdf5-format/src/fractal_heap.rs
+201 -40
View File
@@ -669,15 +669,20 @@ impl FractalHeapHeader {
let iblock_header = 5 + offset_size as usize + block_offset_bytes;
let tw = self.table_width as u64;
let nrows_usize = nrows as usize;
let mut current_heap_offset = iblock_heap_offset;
// Rows below max_direct_rows hold direct blocks; rows at/above hold
// child indirect blocks. (NOT the FRHP "starting rows" field.)
let start_indirect = self.max_direct_rows();
let max_direct_rows = nrows_usize.min(start_indirect);
// The block up to its last child entry, in one window: every
// position read below lies inside it, so its bounds checks are the
// The block up to its last child entry. The walk below reads
// entries in order and stops at the one covering the target, which
// the geometry alone locates, so the first window ends there: a
// header claiming a huge table costs a read of the entries in front
// of the target, not of the rest of the file. Only when that entry
// is unallocated (or none covers the target) does the walk go on,
// over the whole block. Either window holds what it was asked for or
// ends at the end of the file, so its bounds checks are the
// whole-file ones.
let direct_entry = usize::from(offset_size)
+ if self.filter_pipeline.is_some() {
@@ -685,21 +690,129 @@ impl FractalHeapHeader {
} else {
0
};
let entries =
|rows: usize, entry: usize| rows.saturating_mul(tw as usize).saturating_mul(entry);
let block_len = iblock_header
.saturating_add(entries(max_direct_rows, direct_entry))
.saturating_add(entries(
nrows_usize.saturating_sub(start_indirect),
usize::from(offset_size),
));
let w = Window::read(file, iblock_addr as u64, block_len)?;
let direct_entries = max_direct_rows.saturating_mul(tw as usize);
let entries_len = |n: usize| {
n.min(direct_entries)
.saturating_mul(direct_entry)
.saturating_add(
n.saturating_sub(direct_entries)
.saturating_mul(usize::from(offset_size)),
)
};
let all_entries = direct_entries.saturating_add(
nrows_usize
.saturating_sub(start_indirect)
.saturating_mul(tw as usize),
);
let block_len = iblock_header.saturating_add(entries_len(all_entries));
let target_entry = self.indirect_entry_for(nrows_usize, iblock_heap_offset, target_offset);
let first_len = target_entry.map_or(block_len, |i| {
iblock_header
.saturating_add(entries_len(i.saturating_add(1)))
.min(block_len)
});
let mut next = self.walk_indirect_block(
&Window::read(file, iblock_addr as u64, first_len)?,
nrows_usize,
iblock_heap_offset,
target_offset,
offset_size,
target_entry.map_or(usize::MAX, |i| i.saturating_add(1)),
)?;
if next.is_none() && first_len < block_len {
next = self.walk_indirect_block(
&Window::read(file, iblock_addr as u64, block_len)?,
nrows_usize,
iblock_heap_offset,
target_offset,
offset_size,
usize::MAX,
)?;
}
match next {
Some(IndirectChild::Direct(block)) => {
self.read_from_direct_block(file, block, target_offset, length)
}
Some(IndirectChild::Indirect {
addr,
nrows,
heap_offset,
}) => self.read_from_indirect_block(
file,
addr,
nrows,
heap_offset,
target_offset,
length,
offset_size,
depth_remaining - 1,
),
None => Err(FormatError::UnexpectedEof {
expected: target_offset as usize + length,
available: len_usize(file),
}),
}
}
/// Which child entry of an indirect block (numbered in walk order:
/// direct rows, then indirect rows) covers `target_offset`, from the
/// doubling-table geometry alone — the entry
/// [`Self::walk_indirect_block`] stops at if it is allocated. `None`
/// when no entry does.
fn indirect_entry_for(&self, nrows: usize, heap_offset: u64, target: u64) -> Option<usize> {
// The walk adds block sizes with saturation; in u128 the same test
// is `cur <= target < cur + size` without it (a target of u64::MAX
// is never inside a saturated range).
if target == u64::MAX {
return None;
}
let (tw, target) = (u128::from(self.table_width), u128::from(target));
let mut cur = u128::from(heap_offset);
let mut before = 0usize;
for row in 0..nrows {
if target < cur {
return None;
}
// Direct and indirect rows alike span this row's block size per
// entry.
let size = u128::from(self.block_size_for_row(row));
let span = size * tw;
if size > 0 && target < cur + span {
let col = usize::try_from((target - cur) / size).ok()?;
return before.checked_add(col);
}
cur += span;
before = before.saturating_add(self.table_width as usize);
}
None
}
/// Walk an indirect block's child entries in order, in the window `w`
/// (the block from its signature on), and return the allocated child
/// covering `target_offset`, or `None` when no entry among the first
/// `limit` does.
fn walk_indirect_block(
&self,
w: &Window<'_>,
nrows: usize,
iblock_heap_offset: u64,
target_offset: u64,
offset_size: u8,
limit: usize,
) -> Result<Option<IndirectChild>, FormatError> {
let ensure_len = |_: &[u8], pos: usize, needed: usize| w.ensure(pos, needed);
let read_offset = |_: &[u8], pos: usize, size: u8| {
w.ensure(pos, usize::from(size))?;
read_offset(&w.bytes, pos, size)
};
let file_data: &[u8] = &w.bytes;
let block_offset_bytes = (self.max_heap_size as usize).div_ceil(8);
let iblock_header = 5 + offset_size as usize + block_offset_bytes;
let tw = self.table_width as u64;
let mut current_heap_offset = iblock_heap_offset;
let start_indirect = self.max_direct_rows();
let max_direct_rows = nrows.min(start_indirect);
let mut walked = 0usize;
// Parse indirect block header
ensure_len(file_data, 0, 4)?;
@@ -712,6 +825,10 @@ impl FractalHeapHeader {
let block_size = self.block_size_for_row(row);
for _col in 0..tw {
if walked == limit {
return Ok(None);
}
walked += 1;
let child_addr = read_offset(file_data, pos, offset_size)?;
pos += offset_size as usize;
@@ -738,18 +855,13 @@ impl FractalHeapHeader {
&& target_offset >= current_heap_offset
&& target_offset < block_end
{
return self.read_from_direct_block(
file,
DirectBlock {
addr: child_addr as usize,
size: block_size,
heap_offset: current_heap_offset,
filtered_size,
filter_mask,
},
target_offset,
length,
);
return Ok(Some(IndirectChild::Direct(DirectBlock {
addr: child_addr as usize,
size: block_size,
heap_offset: current_heap_offset,
filtered_size,
filter_mask,
})));
}
current_heap_offset = block_end;
}
@@ -758,11 +870,15 @@ impl FractalHeapHeader {
// Rows at and above `start_indirect` hold child indirect blocks. A
// child in row r spans exactly that row's block size of heap space,
// so it has as many rows as a table of that total size needs.
for row in start_indirect..nrows_usize {
for row in start_indirect..nrows {
let child_space = self.block_size_for_row(row);
let child_nrows = self.rows_for_size(child_space);
for _col in 0..tw {
if walked == limit {
return Ok(None);
}
walked += 1;
let child_addr = read_offset(file_data, pos, offset_size)?;
pos += offset_size as usize;
@@ -771,25 +887,16 @@ impl FractalHeapHeader {
&& target_offset >= current_heap_offset
&& target_offset < block_end
{
return self.read_from_indirect_block(
file,
child_addr as usize,
child_nrows,
current_heap_offset,
target_offset,
length,
offset_size,
depth_remaining - 1,
);
return Ok(Some(IndirectChild::Indirect {
addr: child_addr as usize,
nrows: child_nrows,
heap_offset: current_heap_offset,
}));
}
current_heap_offset = block_end;
}
}
Err(FormatError::UnexpectedEof {
expected: target_offset as usize + length,
available: len_usize(file),
})
Ok(None)
}
/// Number of rows in the doubling table whose block size is at most the
@@ -833,6 +940,16 @@ impl FractalHeapHeader {
/// A managed direct block's location, extent and (for a filtered heap) its
/// stored size and filter mask.
/// The child of an indirect block that covers a heap offset.
enum IndirectChild {
Direct(DirectBlock),
Indirect {
addr: usize,
nrows: u16,
heap_offset: u64,
},
}
struct DirectBlock {
addr: usize,
size: u64,
@@ -1151,6 +1268,50 @@ mod tests {
}
}
/// A header claiming a huge doubling table (width 0xFFFF, 0xFFFF rows in
/// the root indirect block) in a 16 MiB file: reading an object from the
/// table's first block reads the entries up to it, not the rest of the
/// file, and gives what the slice read gives. When the covering entry is
/// unallocated the walk goes on over the whole block, still identically.
#[test]
fn huge_table_claims_read_only_what_the_walk_needs() {
use crate::storage::CountingStorage;
let (mut file, _) = build_simple_heap(8, 8);
file.resize(16 << 20, 0);
file[600..604].copy_from_slice(b"FHIB");
let first_entry = 600 + 5 + 8 + 2;
file[first_entry..first_entry + 8].copy_from_slice(&256u64.to_le_bytes());
let mut hdr = FractalHeapHeader::parse(&file, 0, 8, 8).unwrap();
hdr.table_width = 0xFFFF;
hdr.root_block_address = 600;
hdr.current_rows_in_root_indirect_block = 0xFFFF;
let managed_id = |offset: u64, len: u64| {
let payload = offset | (len << 16);
let mut id = vec![0u8];
id.extend_from_slice(&payload.to_le_bytes()[..6]);
id
};
let storage = CountingStorage::new(file.clone());
let id = managed_id(15, 13);
let want = hdr.read_managed_object(&file, &id, 8);
assert!(want.is_ok(), "{want:?}");
storage.reset();
assert_eq!(hdr.read_managed_object_in(&storage, &id, 8), want);
assert!(
storage.bytes_read() < 1024,
"{} bytes in {} reads",
storage.bytes_read(),
storage.reads()
);
// The second entry (heap offsets 128..256) is unallocated (zero is
// not the undefined address, so make it all ones).
file[first_entry + 8..first_entry + 16].fill(0xFF);
let storage = CountingStorage::new(file.clone());
let id = managed_id(130, 4);
let want = hdr.read_managed_object(&file, &id, 8);
assert_eq!(hdr.read_managed_object_in(&storage, &id, 8), want);
}
/// A huge object found through the huge-object B-tree needs the whole
/// file in memory until the B-tree reader is converted: a clean error
/// on other storage.