ALSA: timer: don't re-enter an instance callback that is still running

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Summary

CVECVE-2026-68200
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-10 13:20:07 UTC
Updated2026-08-10 13:20:07 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: ALSA: timer: don't re-enter an instance callback that is still running The userspace-driven timer (utimer) TRIGGER ioctl calls snd_timer_interrupt() directly with no serialization, so two threads triggering the same utimer can run snd_timer_interrupt() on one snd_timer concurrently. snd_timer_process_callbacks() drops timer->lock around each instance callback and marks the in-flight callback with the single SNDRV_TIMER_IFLG_CALLBACK bit; snd_timer_close_locked() waits on that bit to drain an in-flight callback before freeing the instance. The bit cannot represent two concurrent callbacks: when a second interrupt re-queues an instance whose callback is still running, both run at once, the first to finish clears the bit, and the close-path drain then frees the instance (and its callback_data) while the other callback is still live - a use-after-free reachable by any user able to open /dev/snd/timer, both via a user timer instance and via a sequencer queue timer bound to the utimer. snd_timer_interrupt() sets IFLG_CALLBACK before dropping timer->lock, so a concurrent interrupt already observes it under the lock. Skip re-queuing an instance (and its slaves) to the ack/sack list while its callback is in flight; the accumulated pticks are delivered on the next tick, so no event is lost.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 37745918e0e7575bc40f38da93a99b9fa6406224 996c24377eea4d4506b7c3ccbbf1e490440b5e0b git Not specified
CNA Linux Linux affected 37745918e0e7575bc40f38da93a99b9fa6406224 1395327a96614885552bae5fbb650e6dd182d49b git Not specified
CNA Linux Linux affected 37745918e0e7575bc40f38da93a99b9fa6406224 c1078130a4cd7e738f4b73afe99b3e68cbfbf884 git Not specified
CNA Linux Linux affected 37745918e0e7575bc40f38da93a99b9fa6406224 70d28bfcd6224eed75986b3b987b997e59643fa4 git Not specified
CNA Linux Linux affected 6.12 Not specified
CNA Linux Linux unaffected 6.12 semver Not specified
CNA Linux Linux unaffected 6.12.101 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.42 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.6 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2-rc5 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/c1078130a4cd7e738f4b73afe99b3e68cbfbf884 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/70d28bfcd6224eed75986b3b987b997e59643fa4 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/1395327a96614885552bae5fbb650e6dd182d49b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/996c24377eea4d4506b7c3ccbbf1e490440b5e0b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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