Round 3 of the 0.10.1 review, and the finding is the pattern the three rounds
share: each bound an OUTPUT, and the bomb stepped one link along. The
declared size, then the first `FlateDecode`, then every `FlateDecode` -- and
then a link this package had documented as safe.
`ASCII85Decode` was classed as bounded "by its own input because it shrinks".
It quadruples: `z` is the shorthand for four zero bytes. And the output was
never the cost -- `base64.a85decode` appends one 4-byte object per group to a
list, about a hundred bytes of memory per byte of INPUT (101.4x at 1 MiB,
96.1x at 4 MiB, 94.5x at 16 MiB on CPython 3.14).
Paired subprocesses, idle machine, both sides from PINNED trees, the document
built once by a third process and read from a file because `ru_maxrss` never
falls and `b"z" * 64 MiB` alone costs 171 MB:
[/Fl /A85] z x 32 Mi 33 475 B CARRIED 3 261 599 744 -> too_large 42 070 016
[/Fl /A85] z x 64 Mi 66 090 B CARRIED 6 461 558 784 -> too_large 40 280 064
[/A85] z x 8 Mi 8.4 MB CARRIED 933 085 184 -> too_large 62 484 480
[/Fl /A85 /Fl] z x 32 Mi 33 488 B samples_invalid 3 519 180 800 -> too_large 43 438 080
The picture was CARRIED in three of the four: not a bound that fired late, no
bound at all. Doubling the `z` run trebles the old cost and leaves the new one
where it was.
WHY THIS FORM. `assets.MAX_FILTER_DECODE_BYTES` (512 MiB) is what decoding ONE
link may cost -- a separate number from `MAX_IMAGE_BYTES`, because that one
bounds the picture and this one bounds producing it. `FlateDecode` is measured
as it is paid; every other permitted filter carries a MEASURED cost ratio
(`assets.PDF_FILTER_COST_RATIO`) checked against its input BEFORE its decoder
is called, since those decoders take a whole string and return a whole string.
A filter with no ratio is refused unread. The budget TRAVELS: a deflate link
is inflated under the smaller of the picture's bound and what the next link's
decoder may be handed, or `[/Fl /A85]` pays 256 MiB for a refusal.
A chunked ASCII85 decoder written here was the alternative and was FELLED: it
would bound `_check_stream_cost` and not the run, because `stream.get_data()`
decodes the whole chain again with pdfminer's own decoder, and it would make
this package rather than pdfminer the authority on an image's bytes. The cap
is the only number that bounds that. `resource.setrlimit(RLIMIT_AS)` was
MEASURED before anything was built on it, as the order required, and is not
usable: Darwin 26.6.2 raises `ValueError: current limit exceeds maximum limit`
and does not enforce it. No child-process cap exists.
THE CAP IS READ OFF THE CORPORA, the posture `MAX_IMAGE_PIXELS` has: over the
9 668 image objects of the 77 PDFs on this machine, 16 decode through an
ASCII85 link and the largest input to one is 450 739 bytes, against a cap of
about 5.0 MB.
A PROPERTY TEST REPLACES THE LIST OF KNOWN SHAPES: every chain of length 1-3
over the ten filters pdfminer decodes, 1 110 of 1 110, both payload fills,
each delivered under the bound or refused with a published code and never paid
for on the way (`tracemalloc`, which counts allocations and is not disturbed
by load). Known-positive beside it: 258 of 258 chains over the permitted
filters still carry a small image.
MAJOR -- the backstop had no test. `check_payload` at the end of
`_check_stream_cost` could be deleted with the whole suite green, because the
second one after `get_data()` gives the same code one step later. The two
differ in whether the payment was made, so the test asserts `get_data` was
never called.
10 OF 10 MUTANTS KILLED, control green, each killer named in the report. Four
survived a first pass and two tests exist because of it.
NOT ONE PICTURE CHANGES HANDS, MEASURED BY NAME: `_pdf_images` over every PDF
on this machine from both pinned trees -- 9 306 -> 9 306 carried over 77
files, 50 -> 50 on R761, 0 of 78 files moving a count and 0 moving a code.
R761 also settles a question raised while this order was open: 50 objects, 29
[/DCTDecode], 21 [/FlateDecode], 0 ASCII85 links -- so round 2's count of 580
`[/FlateDecode /ASCII85Decode]` objects is reproducible from nothing on this
machine. It changes no decision; a bomb shape does not need a corpus.
Version stays 0.10.1, no tag. README, CHANGELOG, CLAUDE.md and errors.py
corrected TO what the code does; the round-2 report carries a correction block
rather than a rewrite. Report:
docs/2026-09-18-utgangsbudsjett-per-ledd.md
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Kjell Tore Guttormsen
3b3b8ae0ca