Описание
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.
A flaw was found in the Linux kernel's ALSA (Advanced Linux Sound Architecture) sequencer component. An unprivileged local user with access to the sound device can exploit a timing window during the cleanup of a queue timer. This allows the user to re-open a timer that has already been closed, leading to a use-after-free vulnerability. This can result in a system crash (denial of service) or potentially lead to arbitrary code execution.
Отчет
A use-after-free in the ALSA sequencer queue timer path can leave a live timer instance whose callback_data still points to a freed queue. During queue_delete(), snd_seq_timer_close() clears timeri before all outstanding use_lock borrowers have drained. A concurrent SET_QUEUE_CLIENT operation that already holds a queue reference can therefore re-open the timer in this window. The destructor subsequently frees q->timer and the queue without closing the re-opened timer instance, leaving it attached to the global timer with a dangling reference to the freed queue. A later non-owner START can arm the lingering timer instance, and the next timer tick dereferences the freed queue in snd_seq_timer_interrupt().
For CVSS, PR:L is appropriate because the vulnerable path is directly reachable by an unprivileged local user with access to /dev/snd/seq; no capabilities and no queue ownership are required. The issue is not remotely or network reachable and requires local access to the ALSA sequencer interface. AC:H is appropriate because successful exploitation depends on winning a race between queue destruction and timer re-opening.
Successful exploitation can at minimum cause a kernel crash and local denial of service. Because the resulting condition is a kernel use-after-free involving a live callback to a freed object, reuse or manipulation of the freed memory may also allow confidentiality or integrity impact and potentially privilege escalation or arbitrary code execution, although exploitation beyond denial of service has not been demonstrated.
Меры по смягчению последствий
To mitigate this issue, prevent module snd_seq from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically.
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 6 | kernel | Under investigation | ||
| Red Hat Enterprise Linux 7 | kernel | Affected | ||
| Red Hat Enterprise Linux 7 | kernel-rt | Affected | ||
| Red Hat Enterprise Linux 9 | kernel-rt | Affected | ||
| Red Hat Enterprise Linux for NVIDIA 26 | kernel | Not affected | ||
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-8 | Not affected | ||
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-9 | Fix deferred | ||
| Red Hat Enterprise Linux 10 | kernel | Fixed | RHSA-2026:88477 | 23.10.2026 |
| Red Hat Enterprise Linux 8 | kernel-rt | Fixed | RHSA-2026:87374 | 21.10.2026 |
| Red Hat Enterprise Linux 8 | kernel | Fixed | RHSA-2026:87375 | 21.10.2026 |
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Дополнительная информация
Статус:
7 High
CVSS3
Связанные уязвимости
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_inte...
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_in
ALSA: seq: close a re-opened queue timer in the destructor
In the Linux kernel, the following vulnerability has been resolved: A ...
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...
7 High
CVSS3