jxl-grid on 32-bit platforms has an out-of-bounds writes due to integer overflow
Summary
On 32-bit platforms, decoding a crafted image may lead to out-of-bounds writes due to integer overflow in length calculation.
Details & PoC
The test listed below fail under miri with command cargo +nightly miri test --release -p jxl-grid
Or you can use Address Sanitizer, which ignores Rust-specific UB like aliasing but still flags out-of-bounds accesses:
RUSTFLAGS=-Zsanitizer=address cargo +nightly test -Zbuild-std -p jxl-grid --release --target x86_64-unknown-linux-gnu
The following tests should be appended to crates/jxl-grid/src/test/subgrids.rs:
mod miri_ub {
use super::*; // AlignedGrid::with_alloc_tracker computes width * height unchecked. In release, overflow
// can create a tiny backing buffer for huge logical dimensions.
#[test]
fn aligned_grid_dimension_product_overflows() {
let width = usize::MAX / 2 + 1;
let mut grid = AlignedGrid::::with_alloc_tracker(width, 2, None).unwrap();
let mut subgrid = grid.as_subgrid_mut();
*subgrid.get_mut(0, 1) = 1;
std::hint::black_box(grid);
}
}
This issue can be reachable through decoding a crafted image in two ways:
- Huge actual frame
65536 x 65536 passes the current frame area limit (2^32 <= 2^40) but overflows usize element count on 32-bit. Rendering then allocates too-small AlignedGrids in modular/VarDCT/filter paths and later writes through mutable subgrids.
- Huge canvas plus tiny cropped frame
render_frame().Impact
On 32-bit platforms this can cause out-of-bounds writes with attacker-controlled data when decoding a crafted JPEG XL image. This could allow arbitrary code execution.