feat(interop): pin untrusted-decode bounds as a cross-SDK invariant (LAB-2503) - #59
feat(interop): pin untrusted-decode bounds as a cross-SDK invariant (LAB-2503)#5927Bslash6 wants to merge 4 commits into
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…LAB-2503) Readers MUST bound nesting depth (32..=1024) and MUST NOT pre-allocate beyond what the input can back; test-vectors/decode-bounds.json pins 10 reject + 2 accept vectors, generated/verified by tools/decode-bounds-reference.py (stdlib; optional msgpack-python leg). Motivation: LAB-2487 measured nested-header amplification in eager decoders. The 82 MB ceiling previously reported for msgpack-python was an artifact of the array16(10000) probe — array32 headers claiming len(input) reach ~8192x input (10 KB -> 67 MB).
…d tool - rmp-serde is not allocation-free: serde's Vec<T> visitor pre-allocates up to 1 MiB per collection from the declared length; the spec no longer claims slice-based decoders satisfy the allocation rule inherently. - nested_array16/map16 bombs now claim 2000 elements (< input_len) so a per-collection cap of len(input) does not reject them — the vectors must discriminate for msgpack-python too. - Trim repeated measurement prose; verify() drops checks already implied by the recipe equality; 'conformance' wording narrowed to reject/accept.
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WalkthroughThe change defines interop decode bounds for untrusted MessagePack input. It adds shared reject and accept vectors, a Python reference generator and verifier, CI checks, and related protocol documentation. ChangesDecode bounds
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🟠 High · up to The change defines shared MessagePack decode limits, but the current specification does not clearly protect the envelope and does not require overflow-safe slot accounting; malicious inputs could still trigger excessive allocation or bypass rejection. The verification workflow can also pass without importing the pinned dependency, so this PR is not merge-ready until these safeguards and checks are corrected. Sequence Diagram(s)sequenceDiagram
participant VerifyWorkflow
participant DecodeBoundsReference
participant DecodeBoundsVectors
participant MsgpackPython
VerifyWorkflow->>DecodeBoundsReference: run verify
DecodeBoundsReference->>DecodeBoundsVectors: load and compare recipes
DecodeBoundsReference->>MsgpackPython: optionally decode vectors
MsgpackPython-->>DecodeBoundsReference: accept or catchable failure
DecodeBoundsReference-->>VerifyWorkflow: report verification result
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 14.29% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 7 functions across 1 files. (6 skipped: 6 unsupported.) ✨ Finishing Touches 💡 1📝 Generate docstrings 💡
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Narrow the msgpack-python rejection check from `except Exception` to `except ValueError`. Every msgpack unpack error subclasses ValueError (StackError, FormatError, ExtraData, max_*_len, incomplete input) — verified per vector under msgpack 1.0.3, 1.2.1 C extension and 1.2.1 pure-Python fallback. The broad clause was also wrong on the merits: it would have counted a MemoryError as a "conforming rejection", which is the exact failure the spec's failure_mode rule forbids. Now anything that is not a ValueError propagates and fails the run. Report lines move from print() to logging.info on a stdout handler with a message-only format, matching interop-v2-reference.py and file-backend-reference.py; stdout bytes are unchanged. Kody-Resolved: tools/decode-bounds-reference.py:163:specific exception handling Kody-Resolved: tools/decode-bounds-reference.py:175:print statements with logging
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Actionable comments posted: 9
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In @.github/workflows/verify.yml:
- Line 37: Add a mutation test suite for the decode-bounds verifier, using the
existing verifier test patterns in tools/test_wire_format_reference.py and
tools/test_check_version_floors.py. Mutate each vector field and assert that
tools/decode-bounds-reference.py verify fails, then wire this suite into the
mutation-first sequence in verify.yml before the normal verifier invocation.
- Line 46: Update tools/decode-bounds-reference.py to add a require-extras flag
whose ImportError path fails instead of returning the stdlib-only result, then
invoke the verifier in verify.yml with that flag so the optional-deps leg
requires an importable msgpack module.
In `@sdk-feature-matrix.md`:
- Line 288: Update footnote ¹⁶ to include decode-bounds.json and reference the
verify workflow command in .github/workflows/verify.yml. Qualify the Python and
Rust SDK cells to state that their default branches currently lack the
decode-bounds.json fixture and CI verification, unless adding links to
downstream changes that provide this coverage.
In `@spec/interop-mode.md`:
- Around line 457-459: Update the declared_slots accumulation in the
interop-mode pre-allocation validation to use checked or saturating arithmetic,
rejecting arithmetic overflow before comparing against the input-byte budget.
Ensure nested array32 declarations cannot wrap the accumulator and bypass the
“declared slots > input bytes − 1” rejection, and add a regression vector
covering two maximum-declaration array32 headers.
- Around line 474-476: Update the interop-mode specification to define a
concrete maximum SDK input size for valid payloads, require each SDK to enforce
that cap before MessagePack decoding, and document the catchable failure
behavior when the cap is exceeded.
In `@spec/wire-format.md`:
- Around line 381-384: Update the envelope decoding guidance to state that both
envelope_bytes and the payload inside StorageEnvelope are untrusted MessagePack.
Require the structural pre-scan and the Decode bounds from interop-mode.md
before materialising StorageEnvelope, while retaining those bounds for payload
decoding.
- Line 380: Update the rmp-serde safety claim in the wire-format documentation
to remove “inherently,” clarify that declared collection lengths may cause Rust
readers to pre-allocate before child decoding, and require check_structure or an
equivalent pre-scan for Rust consumers.
In `@tools/decode-bounds-reference.py`:
- Line 83: Update the map32_max_claim_alone vector’s declared slot count to use
the pair-to-slot convention, doubling the declared pair count while preserving
its existing overclaim reason; then regenerate test-vectors/decode-bounds.json
via the project’s generate flow.
- Line 135: Add a targeted Ruff FBT001 suppression to the boolean condition
parameter in the check function, preserving the existing positional call sites
and avoiding unrelated signature changes.
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.github/workflows/verify.ymlCHANGELOG.mdsdk-feature-matrix.mdspec/interop-mode.mdspec/wire-format.mdtest-vectors/decode-bounds.jsontools/decode-bounds-reference.py
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Tool (tools/decode-bounds-reference.py): - `--require-extras` (same flag as wire-format-reference.py): a missing msgpack is a failure, so CI's optional-deps leg cannot pass without exercising the real decoder. CLI now fails closed on a flag typo, an unknown mode, two modes, or `generate --require-extras`. - MemoryError/RecursionError from unpackb fail the run naming the vector (the spec's failure_mode rule being violated), instead of a bare trace. - map32_max_claim_alone declared_slots counts pairs as two slots, matching nested_map16_depth_2048 and the field note. - Three new reject vectors, each pinning a distinct implementation error: array32_sum_wraps_u32 (running sum = 2^32 exactly, wraps to 0 in u32), map32_half_claim_wraps_u32_mul (per-header 2 x pairs = 2^32 wraps before the add), fixmap_short_by_one (one-slot-per-pair counting accepts it). msgpack-python 1.0.3 / 1.2.1 C / 1.2.1 pure-Python reject all three. - New mutation suite tools/test_decode_bounds_reference.py (11 guards) runs first in verify.yml, per the workflow's mutation-first doctrine. Spec: - interop-mode: map pair = two slots; per-header terms and the running sum MUST use >= 64-bit or checked/saturating arithmetic; overflow rejects. - wire-format: dropped the false "rmp-serde satisfies this inherently" claim (serde's Vec<T> visitor pre-allocates from declared lengths); the envelope bytes are untrusted MessagePack too, so the decode-bounds pre-scan runs before StorageEnvelope is materialised (Retrieve Flow step 2, now in the read-side conformance list). - Matrix/changelog: decode-bounds vendoring is pending cachekit-py#276 and cachekit-rs#73 (both open), not done; footnote 16 lists the vector file. Rejected (replied on the thread): defining the SDK input-size cap at protocol level — that is a per-deployment sizing decision (LAB-2505). CodeRabbit-Resolved: .github/workflows/verify.yml:37:mutation suite CodeRabbit-Resolved: .github/workflows/verify.yml:46:optional-deps leg CodeRabbit-Resolved: sdk-feature-matrix.md:288:footnote 16 CodeRabbit-Resolved: spec/interop-mode.md:459:overflow-safe slot budget CodeRabbit-Resolved: spec/wire-format.md:380:rmp-serde inherently CodeRabbit-Resolved: spec/wire-format.md:384:envelope decode bounds CodeRabbit-Resolved: tools/decode-bounds-reference.py:83:map32 slot convention CodeRabbit-Resolved: tools/decode-bounds-reference.py:135:FBT001
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| 1. Validate: envelope_bytes.length <= 512 MiB | ||
| 2. Deserialize: envelope = msgpack_decode(envelope_bytes) as StorageEnvelope | ||
| 2. Deserialize: pre-scan envelope_bytes (decode bounds, see Security Limits), then | ||
| envelope = msgpack_decode(envelope_bytes) as StorageEnvelope |
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Violates team rule 'Avoid unsafe type assertions': Detect cases of unsafe type assertions. These do not perform runtime checks and can lead to unexpected runtime errors. Recommend using proper type guards instead.
Prompt for LLM
File spec/wire-format.md:
Line 448:
Violates team rule 'Avoid unsafe type assertions': Detect cases of unsafe type assertions. These do not perform runtime checks and can lead to unexpected runtime errors. Recommend using proper type guards instead.
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| failures = [f for f in results if f] | ||
| for f in failures: | ||
| print("FAIL", f, file=sys.stderr) |
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Violates team rule 'Replace print statements with logging framework': Use the standard logging module (or your app's logger) instead of print() in committed code.
Also found in:
tools/test_decode_bounds_reference.py:101-101
Prompt for LLM
File tools/test_decode_bounds_reference.py:
Line 98:
Violates team rule 'Replace print statements with logging framework': Use the standard logging module (or your app's logger) instead of print() in committed code.
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Crypto/protocol expert-panel gate — PASS (SHIP)Ran the mandatory crypto/protocol expert panel (bug-hunter, security, code-craftsman, catchphrase) at critical stakes against head No blocking findings.
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What & why (LAB-2503)
Follow-up to cachekit-io/cachekit-ts#112 (LAB-2487). cachekit-py and cachekit-rs were bounded against nested-header decode amplification only by their libraries' defaults — no owned invariant, no regression test, and (found while doing this) the premise was wrong: the "82 MB hard ceiling" measured for msgpack-python was an artifact of the
array16(10000)probe. Witharray32headers claiminglen(input)elements the default caps allow ~8 × 1024 × len(input) transient heap (10 KB → 67 MB measured). rmp-serde's 1024-deep default is not safe either: a debug build overflows a 2 MiB thread stack between 512 and 768 nested arrays (uncatchable abort), and serde'sVec<T>visitor pre-allocates up to 1 MiB per level from the declared length.This PR makes the bound a protocol invariant:
spec/interop-mode.md→ Decode bounds (new): readers MUST bound nesting depth (≥ 32, ≤ 1024), MUST NOT pre-allocate beyond what the input can back (Σ declared slots ≤ input bytes − 1; incomplete documents rejected without materialising), and MUST fail closed with a catchable error. Today's SDK values recorded (ts 100, rs 100, py 1024 — the shared number stays #20's open item).test-vectors/decode-bounds.json(new): 10 reject vectors (nestedarray16/map16/array32(len)bombs, a complete 2048-deep spine, over-claimingarray32/map32/bin32/str32, a truncated array) + 2 accept vectors (32-deep nesting, a fully backedarray16) so the bound cannot over-tighten.tools/decode-bounds-reference.py(new, stdlib):generate/verify(recipe equality + depth/slot tag arithmetic; optional msgpack-python reject/accept leg). Wired intoverify.ymlin both Python legs.spec/wire-format.mdSecurity Limits cross-ref, feature-matrix row, CHANGELOG.SDK PRs consuming these vectors: cachekit-io/cachekit-py#276, cachekit-io/cachekit-rs#73.
Review
Expert panel (bug-hunter, security, code-craftsman, catchphrase) at critical stakes — verdict FIX-FIRST, all findings applied in the second commit: the false "rmp-serde satisfies the allocation rule inherently" claim corrected; the
array16/map16bombs now claim 2000 < input_len so a per-collectionlen(input)cap does not already reject them (they must discriminate for msgpack-python); repeated measurement prose trimmed; verify() de-duplicated.Docs
Spec section, wire-format cross-ref, matrix, CHANGELOG all in this diff.
python3 tools/decode-bounds-reference.py verifypasses stdlib-only and with msgpack-python 1.2.1.Summary by CodeRabbit
Security
Documentation
Verification