CVE-2026-89979
massRace condition between trigger-start and hw_params/prepare in Linux kernel ALSA PCM
The Linux kernel's ALSA PCM subsystem contains a race condition in which atomic operations, specifically the trigger (START) command, can run concurrently with non-atomic operations such as hw_params, hw_free, and prepare, because the state checks at the start of those operations do not block atomic ops issued mid-operation. A local attacker who can open a PCM device could trigger this with two threads manipulating the same stream, for example one thread re-issuing PREPARE or HW_PARAMS on an already-prepared stream while another thread triggers START, producing kernel state inconsistency such as the ODEBUG warnings reported by syzkaller and potentially further memory-safety problems. The issue requires low local privileges and no user interaction, and CVSS rates confidentiality, integrity, and availability impact as high, although the kernel developers note serious consequences are usually limited. Any Linux system where untrusted local code can access ALSA PCM device nodes (/dev/snd) is affected, including desktops, embedded/Android devices, and containers or VMs with sound devices exposed. No public proof-of-concept is known, the flaw is not in CISA's KEV, and no in-the-wild exploitation has been reported.
What to do: Install a kernel update containing the upstream ALSA PCM race fix (which uses runtime->buffer_accessing to reject trigger-start while hw_params/hw_free/prepare is in progress) as it reaches your distribution's stable branches. Until patched, restrict access to /dev/snd from untrusted users and avoid exposing sound devices to containers or VMs, and monitor vendor advisories for the specific fixed kernel versions for your branch.
| Linux kernel (ALSA PCM core subsystem) | — |
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
In the Linux kernel, the following vulnerability has been resolved: ALSA: pcm: Fix race between non-atomic ops and trigger-start We protect the races of the concurrent state transitions between atomic PCM ops, but the checks between the non-atomic ops (hw_params, hw_free and prepare) and the atomic ops aren't perfect; there is a check of the conflicting PCM state at the beginning of hw_params & co, but the atomic PCM ops can be still issued during the non-atomic PCM operations. An example such scenario is that a thread A re-issues the PREPARE or HW_PARAMS for the already prepared stream, while another thread B triggers the PCM start in the middle of the prepare operation. Although this usually doesn't lead to much serious issues, it can give some inconsistency as reported by syzkaller (such as ODEBUG warning). There are various atomic PCM ops, and basically the only problem is the PCM start as it operates from the PREPARED state. Other trigger commands (stop, etc) are for the running or the other special state, hence they are filtered as pre-condition. This patch is for preventing the PCM trigger-start during the non- atomic operations in order to address the problems above. Fortunately, the hw_params, hw_free and prepare operations call snd_pcm_buffer_access_lock(), and this can be used for checking the concurrent operations at the PCM trigger -- which sets the runtime->buffer_accessing to a negative (if possible), so the PCM trigger just needs to check the runtime->buffer_accessing value; if it's negative, it means the concurrent non-atomic PCM ops is running.
- Vector
- CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
In the news0 stories
No ingested article mentions this CVE yet.