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LR-IMP-FORMATS: no overflow deciding whether to scale a full-size JPEG decode

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A full-size load asks the decoder for the largest box (`SourceLevel::Full` is
`usize::MAX`, cast to `u32::MAX`). `jpeg::decode` then computed `2 * u32::MAX` to
decide on DCT scaling: an overflow panic in debug builds (caught, so every
full-size JPEG load failed with "decoder panicked"), and a wrap that happened to
give the right answer in release. The comparison saturates now, and the engine
converts its `usize` edge with `u32::try_from` instead of a truncating `as`.

Found decoding camera JPEGs (no JFIF/EXIF header) at full size.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Exalted5373
2026-10-08 16:26:29 -07:00
co-authored by Claude Opus 5.5
parent 7b47ba7894
commit 7173242ab5
2 changed files with 22 additions and 4 deletions
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crates/codecs/src/jpeg.rs
+12 -1
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@@ -165,7 +165,7 @@ pub(crate) fn decode_with_fallback(bytes: &[u8], opts: &DecodeOptions, fallback:
return Err(Error::Malformed(F, "no frame header".into()));
}
check_size(F, m.width as u64, m.height as u64, opts)?;
let scale_to = opts.max_size.filter(|&(mw, mh)| mw > 0 && mh > 0 && (m.width >= 2 * mw || m.height >= 2 * mh));
let scale_to = opts.max_size.filter(|&(mw, mh)| mw > 0 && mh > 0 && (m.width >= mw.saturating_mul(2) || m.height >= mh.saturating_mul(2)));
// zune-jpeg handles the common cases fastest; jpeg-decoder covers DCT scaling, CMYK/YCCK,
// 12-bit and non-interleaved sequential scans (which zune-jpeg 0.5 mis-decodes with subsampling).
let non_interleaved = matches!(m.sof, 0xC0 | 0xC1) && m.first_scan_components < m.components;
@@ -377,6 +377,17 @@ mod tests {
}
}
#[test]
fn unbounded_fit_box_decodes_at_full_size() {
// a full-size load asks for the largest box (`usize::MAX` saturated to `u32::MAX`): no DCT scaling,
// and no overflow working out whether to scale
use crate::{ChromaSubsampling, EncodeImage, EncodeMeta, Samples, encode_jpeg};
let pixels = vec![128u8; 32 * 24 * 3];
let jpeg = encode_jpeg(&EncodeImage::new(32, 24, 3, Samples::U8(&pixels)), 90, ChromaSubsampling::S444, &EncodeMeta::default()).unwrap();
let d = crate::decode(&jpeg, DecodeOptions::fit(u32::MAX, u32::MAX)).unwrap();
assert_eq!((d.width, d.height), (32, 24));
}
#[test]
fn markers_on_garbage() {
assert!(parse_markers(b"").is_none());