CVE-2026-68202: ALSA: seq: close a re-opened queue timer in the destructor

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

ALSA: seq: close a re-opened queue timer in the destructor

queuedelete() closes the queue timer, then frees it. sndseqtimerclose() clears q->timer->timeri. snduselocksync() then drains borrowers, and sndseqtimerdelete() frees q->timer.

A borrower can re-open the timer inside that window. A SETQUEUECLIENT that took a queueptr() uselock reference before the queue was unlinked runs sndseqtimeropen() after the close. Open refuses re-open only while timeri is set, and the close just cleared it, so it re-opens timeri.

sndseqtimerdelete() does not close that instance. Its sndseqtimerstop() is a no-op, because running was cleared first. So it frees q->timer with the instance still live. The queue is freed next.

The instance stays on the global timer with callbackdata pointing at the freed queue. A non-owner START on the unlocked queue arms it. The next tick derefs the freed queue in sndseqtimerinterrupt().

Reachable by an unprivileged user with access to /dev/snd/seq. No CAP and no queue ownership required.

Close any lingering instance in the destructor. There, ->timeri can no longer change: the queue is unlinked and all uselock borrowers have drained, so no sndseqqueueuse() can re-open it. Close it before clearing q->timer. sndtimerclose() waits for any in-flight sndseqtimerinterrupt() to finish, and that callback still reads q->timer (via sndseqcheckqueue()), so q->timer must stay valid until it drains.