fuzz: posix: widen fuzz framing length to 2 bytes#10956
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Pull request overview
This PR updates the POSIX IPC fuzzing harness framing to use a 2-byte little-endian length prefix so libFuzzer can generate IPC messages large enough to exercise IPC4’s larger message envelope and improve coverage of large-config/vendor-config related paths.
Changes:
- Switch fuzz input framing from a 1-byte (×2) length prefix to a 2-byte little-endian byte-count prefix.
- Introduce
POSIX_FUZZ_HDR_LENand update header arithmetic (copy/memmove) accordingly. - Update the in-file protocol documentation to reflect the new framing and rationale.
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The fuzz harness in posix/ipc.c frames each IPC message using a length prefix at the start of the libFuzzer input buffer. Until now this prefix was a single byte multiplied by 2, encoding a maximum per-message payload of 510 bytes. That fits IPC3 (SOF_IPC_MSG_MAX_SIZE = 384) but caps IPC4 at ~12% of its 4096-byte envelope, hiding the entire large_config / vendor_config / pipeline-state-data path family from coverage feedback. Replace the prefix with two little-endian bytes, encoding lengths up to 65535 (still clamped to SOF_IPC_MSG_MAX_SIZE - 4 in code). The remainder of the framing logic is mechanically updated to consume two header bytes per message. Introduce POSIX_FUZZ_HDR_LEN to keep header arithmetic self-documenting. Existing IPC3 and IPC4 corpora are reinterpreted under the new header: what was previously a length byte becomes the low byte of a 16-bit length, with the next byte becoming the high byte. libFuzzer's mutation engine re-discovers productive frame shapes within minutes of running, so the corpora are kept rather than regenerated. Signed-off-by: Tomasz Leman <tomasz.m.leman@intel.com>
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The fuzz harness in posix/ipc.c frames each IPC message using a length prefix at the start of the libFuzzer input buffer. Until now this prefix was a single byte multiplied by 2, encoding a maximum per-message payload of 510 bytes. That fits IPC3 (SOF_IPC_MSG_MAX_SIZE = 384) but caps IPC4 at ~12% of its 4096-byte envelope, hiding the entire large_config / vendor_config / pipeline-state-data path family from coverage feedback.
Replace the prefix with two little-endian bytes, encoding lengths up to 65535 (still clamped to SOF_IPC_MSG_MAX_SIZE - 4 in code). The remainder of the framing logic is mechanically updated to consume two header bytes per message. Introduce POSIX_FUZZ_HDR_LEN to keep header arithmetic self-documenting.
Existing IPC3 and IPC4 corpora are reinterpreted under the new header: what was previously a length byte becomes the low byte of a 16-bit length, with the next byte becoming the high byte. libFuzzer's mutation engine re-discovers productive frame shapes within minutes of running, so the corpora are kept rather than regenerated.