The Program Stream demuxer appended every fed byte and enforced its 4 MiB
cap only inside a branch reached once a start code had been found. Input
containing no start code anywhere therefore hit no cap at all, and since a
whole title is fed through this demuxer, a zero-filled or ciphertext VOB
extent buffered the entire title — up to ~90 GB. When the buffer holds no
start code, only a two-byte `00 00` prefix can begin a PS unit on the next
feed, so that is kept and the rest dropped. The bound is exact rather than
a heuristic: a start code can straddle a feed boundary by at most its
first two bytes, so no real byte is discarded, and a test feeding
`FF FF 00 00` then `01 E0 ...` pins that.
The existing test named for this case fed a real start code first, so the
cap it exercised was the in-PES one. Renamed to say what it covers.
The BD-J label path had a different shape to anything found so far: the
cap is on the COMPRESSED size of a disc file while the allocation scales
with the decompressed size. A `.class` gated only by a path prefix
inflates to the 64 MiB ceiling, yielding ~33M retained strings from `ldc`
operands or ~67M pushes onto a symbolic stack whose depth was unbounded
despite the Code attribute's own `max_stack` being parsed and then
ignored. Bounded both, the stack by `max_stack` itself (JVMS §4.7.3).
The VMG TT_SRPT title count is an untrusted u16 with no de-duplication,
so ~800 KB of crafted IFO re-parsed one PGC 65535 times. Capped at 99, the
DVD-Video maximum, so no conformant disc is clipped.
Every cap carries stated headroom against real media, and each has a test
locking that real media still passes.
I rewrote three of the new assertions before landing them. They compared
the result against the very constant under test — `total <= MAX_TT_SRPT_TITLES`
— which passes vacuously the moment someone raises the constant, the most
likely future regression and the seventh instance of this tautology shape
in this audit. They now assert literals derived from the spec.
The TT_SRPT fixture also had to change: with 65535 identical entries the
de-duplication collapsed them on its own and the cap was never what
bounded the result, so the test passed with the cap removed entirely.
Distinct entries defeat dedup and leave the cap as the only guard;
de-duplication now has its own fixture. Verified by raising each of the
three constants and confirming all three tests fail.
Matthew Jackson
3f7d7af472