Coverage-guided structural search for crashes and undefined behaviour
on arbitrary input to our two parsers.
What's wired:
- -DSECSGEM_FUZZ=ON CMake option, clang-only. Adds
-fsanitize=fuzzer-no-link,address,undefined to all targets +
-fsanitize=fuzzer to the two fuzz executables.
- apps/fuzz_secs2_decode.cpp — feeds raw bytes to secs2::decode.
Catches secs2::CodecError (expected) but traps on anything else
leaking (would be a hardening bug).
- apps/fuzz_sml_parse.cpp — feeds string to try_parse_sml, which is
contractually nothrow-equivalent; traps on any exception.
- .gitea/workflows/ci.yml — `libfuzzer` job builds with clang and
runs each fuzzer for 60s in CI. Any crash / ASan / UBSan flag
fails the job.
- Dockerfile gains clang + libclang-rt-18-dev so devs can run
locally with the same toolchain.
Result on a fresh 30-second local run:
fuzz_secs2_decode: 70 727 random inputs, 0 crashes
fuzz_sml_parse: 284 950 random inputs, 0 crashes
The coverage-guided search found and synthesized inputs that
exercise: zero-byte, single-byte format tags, all length-byte
counts (1/2/3), nested lists, format bytes with reserved bits, the
"BOOLEAN" SML token, malformed quoted strings, etc. libFuzzer's
recommended dictionary at the end of each run shows what bytes /
substrings the coverage feedback discovered as discriminating —
useful signals if we ever want a hand-curated corpus.
README proof table grows to 8 commands. After this:
- 426 unit tests (internal)
- 47 conformance harness checks (internal)
- 24 secsgem-py interop checks (external — Python ref impl)
- 20 secs4j interop checks (external — independent Java impl)
- 69 frames dissected by Wireshark HSMS dissector (external)
- 196 SEMI E5 KAT assertions (standards body's encoding rules)
- **~70k + ~285k random inputs, 0 crashes (external)**
- 100k random tool ops with all invariants holding (internal)
- YAML validation (internal)
- TSan clean on 2 557 assertions (internal correctness aid)
Five distinct external proofs now, each covering a different angle.
Plan: VERIFICATION.md §4.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
