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().
Published: 2026-10-14
Score: n/a
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
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History

Wed, 14 Oct 2026 13:45:00 +0000

Type Values Removed Values Added
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().
Title locking/lockdep: Invalidate stale class_cache entries for zapped classes
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-10-14T13:25:59.676Z

Reserved: 2026-09-25T10:25:14.346Z

Link: CVE-2026-98398

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-10-14T14:17:50.760

Modified: 2026-10-14T14:17:50.760

Link: CVE-2026-98398

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

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Weaknesses

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