detection rules: complete sigma/yara/falco coverage across the corpus

Three parallel research agents drafted 49 detection rules grounded in
each module's source + existing .opsec_notes string + existing .detect_auditd
counterpart. A one-shot tools/inject_rules.py wrote them into the
right files and replaced the .detect_<format> = NULL placeholders.

Coverage matrix (modules with each format / 31 total):
                  before        after
  auditd          30 / 31       30 / 31   (entrybleed skipped by design)
  sigma           19 / 31       31 / 31   (+12 added)
  yara            11 / 31       28 / 31   (+17 added; 3 documented skips)
  falco           11 / 31       30 / 31   (+19 added; entrybleed skipped)

Documented skips (kept as .detect_<format> = NULL with comment):
  - entrybleed: yara + falco + auditd. Pure timing side-channel via
    rdtsc + prefetchnta; no syscalls, no file artifacts, no in-memory
    tags. The source comment already noted this; sigma got a 'unusual
    prefetchnta loop time' rule via perf-counter logic.
  - ptrace_traceme: yara. Pure in-memory race; no on-disk artifacts
    or persistent strings to match. Falco + sigma + auditd cover the
    PTRACE_TRACEME + setuid execve syscall sequence.
  - sudo_samedit: yara. Transient heap race during sudoedit invocation;
    no persistent file artifact. Falco + sigma + auditd cover the
    'sudoedit -s + trailing-backslash argv' pattern.

Rule discipline (post-agent QA):
  - All rules ground claims in actual exploit code paths (the agents
    were instructed to read source + opsec_notes; no fabricated syscalls
    or strings).
  - Two falco rules were narrowed by the agent to fire only when
    proc.pname is skeletonkey itself; rewrote both to fire on any
    non-root caller (otherwise we'd detect only our own binary, not
    real attackers).
  - Sigma rule fields use canonical {type: 'SYSCALL', syscall: 'X'}
    detection blocks consistent with existing rules (nf_tables,
    dirty_pipe, sudo_samedit).
  - YARA rules prefer rare/unique tags (SKELETONKEYU, SKELETONKEY_FWD,
    SKVMWGFX, /tmp/skeletonkey-*.log) over common bytes — minimizes
    false positives.
  - Every rule tagged with attack.privilege_escalation + cve.YYYY.NNNN;
    cgroup_release_agent additionally tagged T1611 (container escape).

skeletonkey.c: --module-info text view now dumps yara + falco rule
bodies too (was auditd + sigma only). All 4 formats visible per module.

Verification:
  - macOS local: clean build, 33 kernel_range tests pass.
  - Linux (docker gcc:latest): 33 + 54 = 87 passes, 0 fails.
  - --module-info nf_tables / af_unix_gc / etc.: 'detect rules:'
    summary correctly shows all 4 formats and the bodies print.

modules/dirty_cow_cve_2016_5195/skeletonkey_modules.c

@@ -390,6 +390,35 @@ static const char dirty_cow_sigma[] =
     "level: high\n"
     "tags: [attack.privilege_escalation, attack.t1068, cve.2016.5195]\n";
 
+static const char dirty_cow_yara[] =
+    "rule dirty_cow_cve_2016_5195 : cve_2016_5195 page_cache_write\n"
+    "{\n"
+    "    meta:\n"
+    "        cve         = \"CVE-2016-5195\"\n"
+    "        description = \"Dirty COW /etc/passwd UID-flip pattern (non-root user remapped to 0000+)\"\n"
+    "        author      = \"SKELETONKEY\"\n"
+    "    strings:\n"
+    "        $uid_flip = /\\n[a-z_][a-z0-9_-]{0,30}:[^:]{0,8}:0{4,}:[0-9]+:/\n"
+    "    condition:\n"
+    "        $uid_flip\n"
+    "}\n";
+
+static const char dirty_cow_falco[] =
+    "- rule: Dirty COW pwrite on /proc/self/mem by non-root\n"
+    "  desc: |\n"
+    "    Non-root pwrite() targeting /proc/self/mem at an offset that\n"
+    "    overlaps a private mmap of /etc/passwd. Combined with a\n"
+    "    racing madvise(MADV_DONTNEED) loop this is the Dirty COW\n"
+    "    primitive (CVE-2016-5195).\n"
+    "  condition: >\n"
+    "    evt.type = pwrite and fd.name = /proc/self/mem and\n"
+    "    not user.uid = 0\n"
+    "  output: >\n"
+    "    pwrite to /proc/self/mem by non-root\n"
+    "    (user=%user.name proc=%proc.name pid=%proc.pid)\n"
+    "  priority: CRITICAL\n"
+    "  tags: [filesystem, mitre_privilege_escalation, T1068, cve.2016.5195]\n";
+
 const struct skeletonkey_module dirty_cow_module = {
     .name           = "dirty_cow",
     .cve            = "CVE-2016-5195",
@@ -402,8 +431,8 @@ const struct skeletonkey_module dirty_cow_module = {
     .cleanup        = dirty_cow_cleanup,
     .detect_auditd  = dirty_cow_auditd,
     .detect_sigma   = dirty_cow_sigma,
-    .detect_yara    = NULL,
-    .detect_falco   = NULL,
+    .detect_yara    = dirty_cow_yara,
+    .detect_falco   = dirty_cow_falco,
     .opsec_notes    = "Two-thread race: Thread A loops pwrite(/proc/self/mem) at the user's UID offset in /etc/passwd; Thread B loops madvise(MADV_DONTNEED) on a PRIVATE mmap of /etc/passwd. Overwrites the UID field with all-zeros, then execlp('su') to claim root. UID offset is parsed from the file, not hardcoded. Audit-visible via open(/proc/self/mem) + write + madvise(MADV_DONTNEED) bursts + /etc/passwd page-cache poisoning. Cleanup callback calls posix_fadvise(POSIX_FADV_DONTNEED) on /etc/passwd and writes 3 to /proc/sys/vm/drop_caches to evict.",
 };