modules: add bad_epoll (CVE-2026-46242, "Bad Epoll" epoll teardown race UAF)

Jaeyoung Chung's kernelCTF "Bad Epoll": a race-condition use-after-free in
fs/eventpoll.c. ep_remove() clears file->f_ep under f_lock but keeps using
the file (hlist_del_rcu + unlock) while a concurrent __fput() frees the
still-referenced struct eventpoll. Reachable by any unprivileged user with
no userns / CONFIG / capability; weaponised via cross-cache to a struct
file, /proc/self/fdinfo arb-read, and ROP. Introduced 58c9b016e128 (6.4),
fixed a6dc643c6931 (7.1-rc1), stable backport 7.0.13. CWE-416; not in KEV.

The corpus's first epoll / VFS-teardown module. Shipped as a reconstructed,
deliberately under-driven trigger on the stackrot / nft_catchall contract:
detect() is a pure version gate (>= 6.4 and below the on-branch fix; no
userns precondition -- epoll needs none); exploit() forks a CPU-pinned
child that exercises the ep_remove-vs-__fput close window a hard-bounded 48
attempts / 2s and returns EXPLOIT_FAIL. It does not grind the race to a
win, does not do the cross-cache reclaim, and does not bundle the fdinfo
R/W + ROP (a won race frees a live struct file and rarely trips KASAN ->
silent-corruption risk).

Wired: registry, Makefile, safety rank (12 -- lowest in the corpus; a
kernel race is the least predictable class), 5 detect() test rows (version
gating), CVE metadata (sorted insert, CWE-416 / T1068 / not-KEV), README +
CVES.md + website counts (44/39), RELEASE_NOTES v0.9.12, and a verify-vm
target (sweep pending). Detection rules are intentionally weak/structural
(epoll ubiquitous, rarely KASAN) -- post-exploitation euid-0 transition,
no yara. Also corrects pre-existing README drift in the "not yet verified"
count (8 -> 11). Not VM-verified, so the verified count stays 28 of 39.
Version 0.9.12. Credit: Jaeyoung Chung (J-jaeyoung).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KUq4DGXSPBmPkAyJ9WnM9n

tools/verify-vm/targets.yaml

@@ -324,3 +324,12 @@ nft_catchall:
   kernel_version: "6.1.163"
   expect_detect: VULNERABLE
   notes: "CVE-2026-23111; nf_tables nft_map_catchall_activate abort-path UAF (inverted '!'). Public reproduction by FuzzingLabs; fixed upstream f41c5d1, Debian backports 6.1.164 (bookworm) / 6.12.73 (trixie) / 6.18.10 (sid); 5.10/bullseye still unfixed. detect() version-gates (catch-all set elements ~5.13; thresholds 6.1.164/6.12.73/6.18.10) AND requires unprivileged user_ns clone — a vulnerable kernel with userns locked (apparmor_restrict_unprivileged_userns / sysctl 0) is PRECOND_FAIL. exploit() forks an isolated child that builds a verdict map with a catch-all GOTO element and provokes an aborting batch to drive the abort-path UAF, observes nft_chain/cg-256 slabinfo, returns EXPLOIT_FAIL (primitive-only). The per-kernel leak + R/W + modprobe_path ROP is NOT bundled, and the trigger is RECONSTRUCTED from public analysis — NOT yet VM-verified. Provisioner: ensure unprivileged userns enabled (sysctl kernel.unprivileged_userns_clone=1 / drop apparmor restriction). A KASAN kernel will oops on a real fire; sweep + trigger validation pending."
+
+# ── bad_epoll (CVE-2026-46242) addition ─────────────────────────────
+
+bad_epoll:
+  box: ubuntu2404
+  kernel_pkg: ""
+  kernel_version: "6.8.0-generic"   # >= 6.4 (bug introduced 58c9b016e128) and below the 7.0.13 backport → VULNERABLE by version
+  expect_detect: VULNERABLE
+  notes: "CVE-2026-46242 'Bad Epoll'; epoll ep_remove-vs-__fput teardown race UAF (Jaeyoung Chung / J-jaeyoung kernelCTF PoC). Introduced 6.4 (58c9b016e128); fixed a6dc643c6931 (7.1-rc1), stable backport 7.0.13 (Debian forky 7.0.13-1 / sid 7.0.14-1); trixie 6.12.x still vulnerable, 6.1/5.10 not affected (code not present). detect() is a PURE version gate — no userns/CONFIG probe, because epoll is reachable by every unprivileged user; on Ubuntu 24.04 stock 6.8.0 (in [6.4, 7.0.13)) it returns VULNERABLE. To also confirm the PATCHED verdict, boot a >= 7.0.13 / 7.1 kernel and expect OK. exploit() forks a CPU-pinned child that builds the epoll race pair (waiter eventpoll watching a target eventpoll) and exercises the ep_remove-vs-__fput concurrent-close window a HARD-BOUNDED 48 attempts / 2s, widening it with close(dup()) false-sharing storms, snapshots the eventpoll/kmalloc-192 slab, and returns EXPLOIT_FAIL. DELIBERATELY UNDER-DRIVEN: a won race frees a live struct eventpoll (real corruption that rarely trips KASAN → possible SILENT destabilisation on a vulnerable host), so the module does NOT grind the race to a win, does NOT perform the cross-cache reclaim, and does NOT bundle the /proc/self/fdinfo arb-read + ROP root-pop. Trigger RECONSTRUCTED from the public kernelCTF PoC — NOT VM-verified. Lowest --auto safety rank (12). Provisioner caution: run only in a throwaway VM/snapshot — even the bounded trigger can, on a rare win, corrupt or panic a vulnerable kernel. Detection is intentionally weak (epoll syscalls ubiquitous); no yara. Sweep + trigger validation pending."