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.