retoorandClaude Opus 4.8
79ae6f27da
Response to incident WA-2026-10-27 (the std::vector max_size() crash). Deep research archived under research/safe-cpp-practices (8 Tier 1, 37 Tier 2, 2 conclusions) on production-safe C++ that keeps development speed: OpenSSF compiler hardening, the C++ Core Guidelines bounds profile, integer-overflow practice, libFuzzer/sanitizer CI, the sanitizer overhead ladder, clang-tidy ratchets. The research prescribed an ASan+UBSan+_GLIBCXX_ASSERTIONS build of the parsers. Standing it up immediately caught a second, independent undefined-behavior bug that two manual reviews had missed: a protobuf varint loop that shifted by up to 70 bits (shift >= 64 is UB) on malformed input. Fixed and guarded by a deterministic test and the sanitizer net. - src/whatsapp/wa_proto.cpp: guard the wire-0 varint shift (the UB). - tests/whatsapp_test.cpp: add an overlong-varint hostile case. - tools/san-whatsapp.sh: the standing sanitizer net for detz::wa parsers. - WaClient frame capture: a frame that fails to decode/dispatch has its exact bytes recorded to <home>/whatsapp/last-error.log (bounded), so the still unreproduced live <iq> failure becomes a one-paste deterministic fix. Wired from the wizard and the whatsapp_send tool. - docs/cpp-safety.md: the project-wide playbook and design decisions (four layers: overflow-safe checked-reader parsing, cheap release hardening, the sanitizer test net, capture). docs/whatsapp.md section 13.6 records the follow-up and the honest open item. AGENTS.md makes it a standing rule; cap.md and mcp.md inherit it for their wire parsers. Verified: build, whatsapp_test (incl. hostile+fuzz), make lint, and tools/san-whatsapp.sh all green; research audit PASS. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
50 lines
2.0 KiB
Markdown
50 lines
2.0 KiB
Markdown
# std::span / subspan: no default bounds checking (cppreference, Embedonix, ModernesCpp)
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## Metadata
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| Field | Value |
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| Institute | Molodetz Institute — Research & Retrieval Division |
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| Subject | safe-cpp-practices |
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| Document type | Source Dossier |
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| Tier | 1 |
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| Source title | std::span / subspan: no default bounds checking (cppreference, Embedonix, ModernesCpp) |
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| Source URL | https://en.cppreference.com/cpp/container/span |
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| Source publisher / author | cppreference.com; Embedonix; ModernesCpp |
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| Source type | vendor docs |
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| Source date (published) | Unknown — not stated |
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| Date researched | 2026-10-27 |
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| Researched by | tai (agent), model: Claude Opus 4.8, on behalf of retoor |
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| Research method | web search synthesis |
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| Confidence | Medium |
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| Status | Active |
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## Summary
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std::span is the right type for a non-owning view of bytes, but its operator[] and subspan do not range-check by default; the parser must validate before it slices.
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## Key findings
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- `subspan` with an offset past the end is undefined behavior; it does not throw.
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- `span::operator[]` has no runtime check in C++20; `at()` only arrives in C++26.
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- For packet parsing, confirm the frame holds header plus the claimed payload length before reading the payload.
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- GSL and tcb::span check preconditions only when NDEBUG is not defined, so bounds checking is an implementation choice, not a standard guarantee.
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## Pros / strengths
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Clear, correct caveat that prevents a false sense of safety from using span.
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## Cons / limitations / caveats
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Synthesized from several secondary pages; the ModernesCpp claim that span checks bounds conflicts with the others and is the weaker reading.
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## Relevance to tai
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detz's decoder is a checked reader over a byte view: it validates length against remaining bytes before every slice, never relying on span/subspan to catch a bad offset.
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## Changelog
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| Date | Change |
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| 2026-10-27 | Initial dossier created (web search synthesis). |
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