CVE-2026-68202

Description

In the Linux kernel, the following vulnerability has been resolved: ALSA: seq: close a re-opened queue timer in the destructor queue_delete() closes the queue timer, then frees it. snd_seq_timer_close() clears q->timer->timeri. snd_use_lock_sync() then drains borrowers, and snd_seq_timer_delete() frees q->timer. A borrower can re-open the timer inside that window. A SET_QUEUE_CLIENT that took a queueptr() use_lock reference before the queue was unlinked runs snd_seq_timer_open() after the close. Open refuses re-open only while timeri is set, and the close just cleared it, so it re-opens timeri. snd_seq_timer_delete() does not close that instance. Its snd_seq_timer_stop() 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 callback_data pointing at the freed queue. A non-owner START on the unlocked queue arms it. The next tick derefs the freed queue in snd_seq_timer_interrupt(). 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 use_lock borrowers have drained, so no snd_seq_queue_use() can re-open it. Close it before clearing q->timer. snd_timer_close() waits for any in-flight snd_seq_timer_interrupt() to finish, and that callback still reads q->timer (via snd_seq_check_queue()), so q->timer must stay valid until it drains.

Predictions

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

References

• https://git.kernel.org/stable/c/fb40d03ed792a8a8bf77aa0ee15df57b0ff78b07
• https://git.kernel.org/stable/c/24f0cabf173539f048946c8fc221131dc221f277
• https://git.kernel.org/stable/c/6a10025c7fd09a7d2af37a3ae1da188569fce470
• https://git.kernel.org/stable/c/31a6163e301d832060f8236f1ed17cbc1ca198df
• https://git.kernel.org/stable/c/2c4dc0ed50b05cd847a4b34b8cebf0775f19aeb9