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CSS: key the DVD crack on the disc, not on the container

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`resolve_dvd_title_key` decided whether to run the DVD CSS crack by asking
what CONTAINER it was looking at — `ContentFormat::MpegPs`. MPEG program
stream is what DVD and HD-DVD have in common, so every HD-DVD title was
run through a crack scan for a copy-protection scheme HD-DVD does not
use and cannot carry: AACS is its family, and CSS appears nowhere on the
disc.

Both outcomes of that scan were wrong. The cheap one wasted up to 50,000
sector reads per title. The expensive one returned `CssKeyMissing` —
E7023 — refusing a perfectly good HD-DVD with a CSS error, which is what
a real CI run produced on the HD-DVD fixture. Reading E7023 there sends
whoever triages it looking for a missing DVD key on a disc that never had
one, which is how a routing bug spends a day disguised as a key problem.

The right axis was already in the codebase and already used: `mux/resolve`
asks `disc.format == DiscFormat::Dvd`. This threads the disc format down
to the decision and adds `DiscFormat::may_have_css` to name the question.

The asymmetry decides the default, so it is worth stating. Running CSS on
an HD-DVD costs a wasted scan or a false refusal — visible, recoverable,
annoying. NOT running it on a real DVD muxes scrambled sectors as
plaintext and exits 0, which is the failure-that-looks-like-success class
this project has shipped once already. So `may_have_css` is false ONLY
for the families proven CSS-free, and `DiscFormat::Unknown` — a bare
reader with no scan behind it — still cracks. An `== Dvd` allow-list
would have read as tighter while silently stranding every caller that
cannot name its disc.

Both directions are pinned: an HD-DVD title must never enter the crack,
and an unknown-format title must still enter it. Removing the disc-format
clause fails the first and leaves the second and every DVD test green.
This commit is contained in:
Matthew Jackson
2026-08-18 19:11:20 -07:00
parent 02e7bc605d
commit 4cd9b7baa1
6 changed files with 302 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/mux/disc.rs
+68 -5
View File
@@ -208,12 +208,25 @@ impl DiscStream {
/// Works with physical drives and ISO files — both implement SectorSource.
/// The caller opens the source, scans for titles/keys, and passes them in.
/// The stream handles demuxing, decryption, and codec parsing internally.
///
/// `content_format` is the CONTAINER (TS vs PS demuxer). `disc_format` is
/// the DISC FAMILY, and it exists as its own parameter because the two are
/// not interchangeable: DVD and HD-DVD are both `ContentFormat::MpegPs`,
/// yet only DVD can carry CSS. It gates the per-title CSS crack below. A
/// caller that genuinely does not know the disc passes
/// [`crate::disc::DiscFormat::Unknown`], which still attempts the crack —
/// the safe direction (see [`crate::disc::DiscFormat::may_have_css`]).
// Eight params is inherent to a constructor that takes the source, the
// title, the keys, both format axes (container and disc family) and the
// read-mode flags; grouping them would only relocate the same fields.
#[allow(clippy::too_many_arguments)]
pub fn new(
mut reader: Box<dyn SectorSource>,
title: DiscTitle,
mut decrypt_keys: crate::decrypt::DecryptKeys,
batch_sectors: u16,
content_format: crate::disc::ContentFormat,
disc_format: crate::disc::DiscFormat,
raw: bool,
halt: Option<Halt>,
) -> std::io::Result<Self> {
@@ -223,17 +236,20 @@ impl DiscStream {
// Resolve this title's CSS key from the reader if the caller supplied
// none — the SAME shared step the file-backed mux highway
// (`build_iso_pipeline`) uses, so single-pass and multi-pass descramble a
// DVD identically. No-op for AACS / already-keyed / genuinely-clear input
// or `raw`; a scrambled-but-uncrackable DVD is a hard `CssKeyMissing`.
// `halt` is passed here (not deferred to `with_halt`) so a Stop during the
// crack scan is honored — the scan runs at construction, before the caller
// can attach a token.
// DVD identically. No-op for a disc format that cannot carry CSS (HD-DVD
// and the BD families — `disc_format`, NOT the MPEG-PS container, which
// DVD and HD-DVD share), for AACS / already-keyed / genuinely-clear
// input, and for `raw`; a scrambled-but-uncrackable DVD is a hard
// `CssKeyMissing`. `halt` is passed here (not deferred to `with_halt`)
// so a Stop during the crack scan is honored — the scan runs at
// construction, before the caller can attach a token.
crate::css::resolve_dvd_title_key(
&mut *reader,
&extents,
&mut decrypt_keys,
batch_sectors,
content_format,
disc_format,
raw,
halt.as_ref(),
)?;
@@ -1202,6 +1218,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8, // request 8 sectors (16384 B); the source delivers 1 (2048 B)
ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)
@@ -1292,6 +1309,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8,
ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)
@@ -1328,6 +1346,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8,
ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)
@@ -1440,6 +1459,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8,
ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)
@@ -1483,6 +1503,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8,
crate::disc::ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)
@@ -1518,6 +1539,7 @@ mod tests {
aacs,
8,
ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)
@@ -1680,6 +1702,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8,
ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)
@@ -1796,6 +1819,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8,
ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)
@@ -1859,6 +1883,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8,
ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)
@@ -1979,6 +2004,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8,
ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)
@@ -2038,6 +2064,7 @@ mod tests {
keys,
8,
ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)
@@ -2137,6 +2164,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8,
ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)
@@ -2181,6 +2209,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8,
crate::disc::ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)
@@ -2238,6 +2267,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8,
ContentFormat::MpegPs,
crate::disc::DiscFormat::Dvd,
false,
None,
);
@@ -2247,6 +2277,36 @@ mod tests {
);
}
/// The HD-DVD counterpart of the test above, pinned at the SAME boundary so
/// the disc-format axis is proven to reach the shared CSS step through this
/// constructor and not just inside `css::resolve_dvd_title_key`.
///
/// Byte-for-byte identical input to `disc_stream_new_dvd_none_scrambled_hard_fails`
/// — same `LockedReader`, same MPEG-PS title, same `None` keys — with only
/// the disc format changed. The DVD case must still be refused (E7023) and
/// the HD-DVD case must construct: an HD-DVD is AACS and has no CSS, so
/// there is no CSS key for it to be missing. Catches the mutation of
/// dropping `disc_format` from `DiscStream::new`'s plumbing (or hardcoding
/// a CSS-capable value there), which is exactly the shape of the shipped
/// defect: E7023 on a perfectly good HD-DVD.
#[test]
fn disc_stream_new_hddvd_none_scrambled_does_not_hard_fail() {
let res = DiscStream::new(
Box::new(LockedReader),
mpegps_title(8),
crate::decrypt::DecryptKeys::None,
8,
ContentFormat::MpegPs,
crate::disc::DiscFormat::HdDvd,
false,
None,
);
assert!(
res.is_ok(),
"an HD-DVD must never be refused for a missing CSS key — it carries no CSS"
);
}
/// `raw` must bypass the CSS crack at the DiscStream boundary too: the same
/// scrambled-uncrackable input that hard-fails above must CONSTRUCT in raw
/// mode (ciphertext passthrough), never hard-fail.
@@ -2258,6 +2318,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8,
ContentFormat::MpegPs,
crate::disc::DiscFormat::Dvd,
true, // raw
None,
);
@@ -2471,6 +2532,7 @@ mod tests {
crate::decrypt::DecryptKeys::None,
8,
ContentFormat::MpegPs,
crate::disc::DiscFormat::Dvd,
false,
None,
)
@@ -2592,6 +2654,7 @@ mod tests {
},
3,
ContentFormat::BdTs,
crate::disc::DiscFormat::BluRay,
false,
None,
)