CVE-2026-97925

In the Linux kernel, the following vulnerability has been resolved:

tick/broadcast: Plug clockevents replacement race

朱恺乾 reported and decoded the following race condition when a broadcast

device is replaced:

CPUA CPUB

__tick_broadcast_oneshot_control()

bc = tick_broadcast_device.evtdev;

tick_install_broadcast_device(dev)

clockevents_exchange_device(cur, dev)

shutdown(cur);

detach(cur);

cur->handler = noop;

tick_broadcast_device.evtdev = dev;

tick_broadcast_set_event(bc, next_event); <- FAIL: arms a detached device.

If the original broadcast device has a restricted interrupt affinity mask

and the last CPU in that mask goes offline then the BUG() in

tick_cleanup_dead_cpu() triggers because the clockevent device is not in

detached state.

The reason for this is that tick_install_broadcast_device() is not

serialized vs. tick broadcast operations.

The obvious cure is to serialize tick_install_broadcast_device() with

tick_broadcast_lock against a concurrent tick broadcast operation.

That requires to split clockevents_exchange_device() into two parts, one

which does the exchange, shutdown and detach operation and the other which

drops the module reference count. This is required because the module

reference cannot be dropped while holding tick_broadcast_lock.

Let clockevents_exchange_device() do both operations as before, but let the

broadcast device code take the two step approach and do the device

exchange under tick_broadcast_lock and drop the module reference count

after releasing it.