lwan: fix broken build

[tc-agent]

Why

The fuzzer build last succeeded on 2026-04-23 (build status dashboard, Fuzz Introspector). Daily builds since have all failed at the compile step in src/lib/lwan-straitjacket.c:

error: use of undeclared identifier 'LANDLOCK_ACCESS_FS_IOCTL_DEV'
error: use of undeclared identifier 'LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET'
error: use of undeclared identifier 'LANDLOCK_SCOPE_SIGNAL'
error: no member named 'scoped' in 'struct landlock_ruleset_attr'

Lwan landed Landlock support in 3cb40844 on the same date. The base-builder image (base-builder:ubuntu-24-04) ships kernel 6.8 headers, which lack symbols introduced in Linux 6.10 (LANDLOCK_ACCESS_FS_IOCTL_DEV) and 6.12 (LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET, LANDLOCK_SCOPE_SIGNAL, scoped struct member). lwan-straitjacket.c uses these unconditionally under LWAN_HAVE_LANDLOCK.

The coverage build also currently fails at the same compile step with the same errors. Its last_successful_build (2025-04-22) is older than the public log retention window, so this fix addresses the currently visible failure but cannot verify whether a separate prior issue exists.

What

Patch CMake at build time to remove the find_path(LANDLOCK_HEADER ...) block, which keeps LWAN_HAVE_LANDLOCK undefined and skips the offending code. The fuzz harnesses (config_fuzzer, h2_huffman_fuzzer, pattern_fuzzer, request_fuzzer, template_fuzzer) target lwan's parsers (config, HTTP/2 Huffman, glob patterns, HTTP requests, templates); the sandboxing code path is not on any harness's reachable graph.

Coverage after fix (5 min/harness, libfuzzer + ASan)

harness	lines	functions
config_fuzzer	1142 (9.5%)	113 (14.2%)
h2_huffman_fuzzer	793 (6.6%)	60 (7.6%)
pattern_fuzzer	700 (5.8%)	58 (7.3%)
request_fuzzer	1496 (12.4%)	133 (16.8%)
template_fuzzer	1327 (11.0%)	127 (16.0%)
total	3322 (27.5%)	284 (35.6%)

[github-actions]

Fuzzing Coverage Report

Tested: project lwan · base c4ba43b → head 9d4fbc2 · 300s total fuzz budget · updated 2026-05-28 05:39 UTC · workflow run

Metric	Before	After	Delta
Static reachability	29.7% (233/784)	29.7% (233/784)	+0.0%
Line coverage	28.4% (3474/12221)	28.0% (3418/12221)	-1.6%
Branch coverage	27.0% (1724/6396)	26.5% (1694/6396)	-1.7%
Function coverage	35.8% (286/800)	35.4% (283/800)	-1.0%

Per-harness

Harness	Lines before	Lines after	Δ
config_fuzzer	10.8% (1311/12179)	10.7% (1305/12179)	-0.5%
h2_huffman_fuzzer	8.0% (973/12144)	8.0% (973/12144)	+0.0%
pattern_fuzzer	7.2% (880/12162)	7.2% (880/12162)	+0.0%
request_fuzzer	14.0% (1697/12144)	13.7% (1667/12144)	-1.8%
template_fuzzer	12.1% (1470/12156)	11.9% (1450/12156)	-1.4%

_{Δ = (after − before) / before, to accommodate that denominators may change. "new" when before is 0; "deleted" when after is 0.}