fix(serializer): own the msgpack decode depth bound and add a structural walk (LAB-2503) - #73
fix(serializer): own the msgpack decode depth bound and add a structural walk (LAB-2503)#7327Bslash6 wants to merge 3 commits into
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…de's 1024) (LAB-2503) Both untrusted decode paths (serializer::deserialize, interop::deserialize) build their Deserializer through bounded_deserializer with an explicit MAX_DECODE_DEPTH. rmp-serde's 1024 default is not a safe bound: a debug build overflows a 2 MiB thread stack (uncatchable abort) between 512 and 768 nested arrays — a ~700-byte forged entry. 100 matches cachekit-ts and sits inside the protocol's 32..=1024 window. Regression-guarded by the vendored protocol decode-bounds vectors.
…503 panel) Panel finding: rmp-serde is not allocation-free — serde's Vec<T> visitor pre-allocates min(declared, 1 MiB) per collection from size_hint, so 50 nested array32(0xFFFFFFFF) headers (250 bytes) cost 50 MiB into a Vec-bearing target before EOF (an OOM kill on a Workers isolate). check_structure() walks headers only (Σ declared ≤ remaining input, fail closed on 0xc1/truncation/overflow) and runs inside bounded_deserializer, so both decode paths get it; interop reads trailing bytes via into_inner. Test: recursive Vec enum target rejected before allocation; docs corrected.
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Included review availability: 0 reviews are currently available. Your included PR review attempts over the past 7 days set your current allowance at 1 review per hour. WalkthroughThe change adds bounded MessagePack deserialisation. It validates structure before allocation, enforces a nesting depth of 100, applies the shared decoder to interop paths, and adds protocol vectors and tests for malformed and valid inputs. ChangesBounded decode protection
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: ⚪ Minimal · up to The change adds bounded decoding and structural validation without any supplied current-head merge-blocking risk; it is merge-ready after normal checks and review. Sequence Diagram(s)sequenceDiagram
participant Backend
participant InteropDecode
participant BoundedDeserializer
participant MessagePackDeserializer
Backend->>InteropDecode: provide MessagePack bytes
InteropDecode->>BoundedDeserializer: decode one document
BoundedDeserializer->>BoundedDeserializer: validate structure and allocation claims
BoundedDeserializer->>MessagePackDeserializer: decode with depth limit 100
MessagePackDeserializer-->>InteropDecode: return decoded value
InteropDecode-->>Backend: return value or Serialization error
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In `@crates/cachekit/src/serializer/mod.rs`:
- Around line 33-38: Verify the current serde cautious size-hint byte cap, then
update both documentation sites: in crates/cachekit/src/serializer/mod.rs lines
33-38, replace the outdated per-collection 1 MiB and MAX_DECODE_DEPTH MiB
figures; in crates/cachekit/tests/decode_bounds_tests.rs lines 143-147, replace
the “50 MiB before EOF” figure and document that #[serde(untagged)] buffers
through serde’s Content rather than the Vec<Tree> visitor. Keep the structural
walk and assertions unchanged.
- Line 119: Update the public rustdoc near MAX_DECODE_DEPTH to render
check_structure as plain text in backticks rather than an intra-doc link, and
replace both occurrences while preserving the MAX_DECODE_DEPTH link.
In `@README.md`:
- Line 202: Update the decode-bounds.json Markdown link in the README to point
to an existing protocol test-vector file, or remove the link if no valid
replacement exists; leave the surrounding decoding description unchanged.
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README.mdcrates/cachekit/src/interop.rscrates/cachekit/src/serializer/mod.rscrates/cachekit/tests/decode_bounds_tests.rscrates/cachekit/tests/vectors/decode-bounds.json
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…ta clippy (LAB-2503) CodeRabbit round on PR #73 plus the red beta lane: - serializer/mod.rs, decode_bounds_tests.rs: restate the serde pre-allocation figure with units — min(declared_len x size_of::<Element>(), 1 MiB) bytes per collection — and note that #[serde(untagged)] targets decode through serde's Content buffer, which uses the same cautious size_hint cap as Vec<T>. The 1 MiB / 50 MiB figures were verified against serde 1.0.228 src/core/private/size_hint.rs and reproduced with a counting allocator (250 B of nested array32 headers -> 50.0 MiB requested); CodeRabbit's "stale figure" premise was wrong, only the units were sloppy. - serializer/mod.rs: check_structure is pub(crate); linking it from public rustdoc trips private_intra_doc_links. Plain code spans now. Also resolved the four pre-existing unresolved module-doc links in interop.rs and memcached.rs (//! docs resolve in the parent scope) so cargo doc is warning-free. - README: decode-bounds.json and interop-mode.json both link the vendored copies the test suite actually runs (upstream decode-bounds.json 404s until protocol#59 merges), with one link to the protocol repo root. - Cargo.lock: async-trait 0.1.89 -> 0.1.92. Rust 1.99 beta clippy's double_must_use fires on the #[must_use] async-trait 0.1.89 injects onto every generated method (Pin<Box<dyn Future>> is already must_use); 0.1.92 removes it (dtolnay/async-trait#303). Adds syn 3.0.4 as a compile-time proc-macro dep alongside syn 2 (MSRV 1.71 <= 1.85; OSV clean; cargo deny passes; crates.io artifacts byte-identical to the 0.1.92 / 3.0.4 tags). Beta clippy, stable clippy, and the 1.85 lane verified locally. CodeRabbit-Resolved: crates/cachekit/src/serializer/mod.rs:38:stale serde pre-allocation CodeRabbit-Resolved: crates/cachekit/src/serializer/mod.rs:119:rustdoc intra-doc link to CodeRabbit-Resolved: README.md:202:dead link to decode-bounds
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What & why (LAB-2503)
interop::deserializeandserializer::deserializedecoded backend-supplied bytes under rmp-serde's defaults. Two problems, both measured here:Vec<T>visitor pre-allocatesmin(declared, 1 MiB)per collection fromsize_hint, so 50 nestedarray32(0xFFFFFFFF)headers (250 bytes) cost 50 MiB into aVec-bearing target before EOF — an OOM kill on a Workers isolate. (serde_json::Valuehappens to allocate nothing, which is why a vectors-only test would not have caught it.)The fix (
serializer/mod.rs)MAX_DECODE_DEPTH = 100— matches cachekit-ts, inside the protocol's32..=1024window; applied asset_max_depth(MAX + 1)because rmp-serde's counter admits n − 1 levels (pinned by test: 100 decodes, 101 rejected).check_structure(bytes)— header-only walk (Σ declared ≤ remaining input at every step; fail closed on0xc1, truncation, length overflow; 32-bit-safe). Allocates nothing.bounded_deserializer(bytes)runs both and is the only way either decode path builds itsDeserializer; interop keeps its strict trailing-bytes rule viainto_inner().Tests
tests/decode_bounds_tests.rs: the protocol'sdecode-bounds.json(vendored, sha-pinned) through both paths on a 2 MiB-stack thread, the 100/101 boundary, and a recursiveVecenum target proving the amplifier is rejected before allocation.cargo testdefault +file,macrosfeature sets green; clippy-D warningswith the CI feature set clean; wasm32cargo checkclean.Review
Expert panel at critical stakes: bug-hunter found the
Vec<T>pre-allocation gap (fixed here — my initial "rmp-serde never pre-allocates" claim was wrong); security NO FINDINGS; craftsman/catchphrase prose cuts applied.Docs
README interop section updated; rustdoc on
MAX_DECODE_DEPTH/check_structureis the canonical rationale. Protocol spec/vectors: cachekit-io/protocol#59. Sibling: cachekit-io/cachekit-py#276.Summary by CodeRabbit
Security & Reliability
Documentation