as an empty directory
On an AACS 2.1 disc the non-forensic gap fill hardcoded pool slot 0 as
"the" base Unit Key, so every content LBA outside a forensic segment was
keyed with CPS unit 1's key even on a disc carrying several CPS units. It
does not fail loudly — it produces garbage plaintext. The gap fill now
resolves each extent's own base key from its ciphertext, sharing the
sampling and slot-picking the multi-CPS path already had rather than
adding a second copy, and memoised in the existing per-disc cache. A disc
with one base key still short-circuits with zero extra reads, which the
existing probe-cost test pins. Forcing the slot back to a constant fails
four tests, so the choice is load-bearing rather than incidental.
A directory ICB whose descriptor tag is neither File Entry nor Extended
File Entry (ECMA-167 4/14.9, 4/14.17) was turned into a successfully-read
EMPTY directory, indistinguishable from a genuinely empty one, while the
same tag on a file ICB was already a hard error. Fifth instance in this
audit of a failure converted into a plausible success value, and the
second in this very function — round 5 fixed a read error becoming a file
size of zero here.
An unrecorded extent (ECMA-167 4/14.14.1.1: allocated but not recorded,
logically zeros that still occupy file space) was dropped entirely rather
than contributing its length, so every later extent landed at the wrong
file offset. Silent corruption, not an error. Extents now carry a recorded
flag and the hole emits zeros without touching the media.
The Volume Descriptor Sequence was swept at hardcoded sectors 32..64 while
the anchor's own Main VDS Extent pointer was parsed into a comment and
ignored; ECMA-167 3/10.2.1 defines that extent by the field, not by
position, so a conformant volume placing it elsewhere failed to mount.
drive_status decoded byte 5 as Media Status without checking the event
header's NEA bit or notification class (MMC-6 §6.7), so a reply carrying
no media event descriptor decoded as "no disc". The drive is untrusted
input here, and this is the works-on-my-drive class.
Two more tests were found asserting the defects they sit next to — one
requiring unrecorded extents to be dropped, one that four drive fixtures
built non-conformant replies the corrected decoder rightly rejects. Both
rewritten. Combined with the DTS one in the previous commit that makes
three tests this round that locked a bug in as intended behaviour, which
is a different and worse failure than the tautological tests found so far:
a tautology fails to catch a regression, these actively defend the defect.
Not fixed, adjacent: extract_one_file streams extents sequentially and
will now READ an unrecorded extent's sectors rather than writing
guaranteed zeros. Offsets are right, and pressed media reads as zeros
there, but it is not zero-guaranteed the way read_file now is; that needs
a recorded flag through PlannedFile.
Matthew Jackson
c63dafcf1a