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/ptrace_traceme_cve_2019_13272/skeletonkey_modules.c

@@ -317,6 +317,42 @@ static const char ptrace_traceme_auditd[] =
     "-a always,exit -F arch=b64 -S ptrace -F a0=0 -k skeletonkey-ptrace-traceme\n"
     "-a always,exit -F arch=b32 -S ptrace -F a0=0 -k skeletonkey-ptrace-traceme\n";
 
+static const char ptrace_traceme_sigma[] =
+    "title: Possible CVE-2019-13272 PTRACE_TRACEME stale-cred LPE\n"
+    "id: 1a02c3a8-skeletonkey-ptrace-traceme\n"
+    "status: experimental\n"
+    "description: |\n"
+    "  Detects ptrace(PTRACE_TRACEME) immediately followed by parent\n"
+    "  execve of a setuid binary. The kernel stores the parent's pre-\n"
+    "  execve credentials on the ptrace_link; after execve the link\n"
+    "  is stale but ptrace still grants privileges. False positives:\n"
+    "  debuggers (gdb, strace) tracing setuid processes legitimately.\n"
+    "logsource: {product: linux, service: auditd}\n"
+    "detection:\n"
+    "  traceme: {type: 'SYSCALL', syscall: 'ptrace', a0: 0}\n"
+    "  execve:  {type: 'SYSCALL', syscall: 'execve'}\n"
+    "  condition: traceme and execve\n"
+    "level: high\n"
+    "tags: [attack.privilege_escalation, attack.t1068, cve.2019.13272]\n";
+
+static const char ptrace_traceme_falco[] =
+    "- rule: PTRACE_TRACEME followed by setuid execve (cred escalation)\n"
+    "  desc: |\n"
+    "    Child calls ptrace(PTRACE_TRACEME) (recording parent's pre-\n"
+    "    execve creds); parent then execve's a setuid binary\n"
+    "    (pkexec, su, sudo). The stale ptrace_link grants the\n"
+    "    unprivileged child ptrace privileges over the now-root\n"
+    "    parent. CVE-2019-13272. False positives: debuggers (gdb,\n"
+    "    strace) tracing setuid processes legitimately.\n"
+    "  condition: >\n"
+    "    evt.type = ptrace and evt.arg.request = PTRACE_TRACEME and\n"
+    "    not user.uid = 0\n"
+    "  output: >\n"
+    "    PTRACE_TRACEME by non-root\n"
+    "    (user=%user.name pid=%proc.pid ppid=%proc.ppid)\n"
+    "  priority: HIGH\n"
+    "  tags: [process, mitre_privilege_escalation, T1068, cve.2019.13272]\n";
+
 const struct skeletonkey_module ptrace_traceme_module = {
     .name           = "ptrace_traceme",
     .cve            = "CVE-2019-13272",
@@ -328,9 +364,9 @@ const struct skeletonkey_module ptrace_traceme_module = {
     .mitigate       = NULL,    /* mitigation: upgrade kernel; OR sysctl kernel.yama.ptrace_scope=2 */
     .cleanup        = NULL,    /* exploit replaces our process image; no cleanup applies */
     .detect_auditd  = ptrace_traceme_auditd,
-    .detect_sigma   = NULL,
+    .detect_sigma   = ptrace_traceme_sigma,
     .detect_yara    = NULL,
-    .detect_falco   = NULL,
+    .detect_falco   = ptrace_traceme_falco,
     .opsec_notes    = "Parent and child cooperate: child calls ptrace(PTRACE_TRACEME) (recording the parent's current credentials), then sleeps; parent execve's a setuid binary (pkexec or su) and elevates. The stale ptrace_link in the child still holds the old (non-root) credentials, so PTRACE_ATTACH succeeds against the now-root parent; the child injects shellcode at the parent's RIP via PTRACE_POKETEXT and detaches. Audit-visible via ptrace with a0=0 (PTRACE_TRACEME) closely followed by execve of a setuid binary in the parent process. No file artifacts; no persistent changes. No cleanup callback - the exploit execs /bin/sh and does not return.",
 };