Bug 2513481 (CVE-2026-68201)

Summary: CVE-2026-68201 kernel: ALSA: timer: drain a slave's callback before its master detaches it
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: high    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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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.
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Description OSIDB Bzimport 2026-08-10 12:39:47 UTC 
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.
Comment 1 Mauro Matteo Cascella 2026-08-11 07:47:55 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081011-CVE-2026-68201-df47@gregkh/T