High [CVE-2026-68201] drain a slave's callback before its master detaches it

In the Linux kernel, the following vulnerability has been resolved: ALSA: timer: drain a slave's callback before its master detaches it snd_timer_close_locked() drains the closing instance's own in-flight callback (IFLG_CALLBACK) before freeing it, but not its slaves'.

When a master instance is closed, remove_slave_links() clears each slave's ->timer; the slave's own close then reads timer == NULL and takes the branch that skips the drain entirely (snd_timer_stop_slave() also no-ops on a NULL timer).

So a slave whose callback is still running when the master is closed is freed underneath the live callback, leading to use-after-free. Drain the slaves too before remove_slave_links() severs them. snd_timer_stop() has already taken this instance off the active list, so no new slave callback can be queued.

Take the slaves off the ack list so a pending one can't fire either, then wait for any that is already in flight. A flaw was found in the ALSA (Advanced Linux Sound Architecture) timer component of the Linux kernel.

When a master timer instance is closed, it does not properly ensure that all associated slave timer callbacks have finished executing before detaching them. This oversight can lead to a use-after-free vulnerability, where a freed memory region is accessed, potentially causing system instability, crashes, or allowing an attacker to execute arbitrary code.