CVE-2026-98314ALSA: pcm: set timer->private_data before registering the PCM timer

Official description

In the Linux kernel, the following vulnerability has been resolved: ALSA: pcm: set timer->private_data before registering the PCM timer snd_pcm_timer_init() calls snd_device_register() to link the new struct snd_timer into the global timer list while it still carries hw.c_resolution = snd_pcm_timer_resolution (and hw.start/hw.stop), and only afterwards sets timer->private_data = substream. Once the timer is on the list under register_mutex, a concurrent reader can already reach it through the same mutex and invoke these callbacks. /proc/asound/timers does this via c_resolution(), and snd_timer_open()+snd_timer_start() reach start()/stop() the same way. All three dereference timer->private_data, which for this brief window is NULL, giving a NULL-pointer dereference: substream = timer->private_data; return substream->runtime ? ... // substream is NULL Move the private_data/private_free assignment before snd_device_register() so the timer is never visible on the list without its private_data set. On the snd_device_register() failure path, private_free() (snd_pcm_timer_free()) can now run, but it only does substream->timer = NULL, which is already NULL at that point since substream->timer is set to the new timer just once, after a successful registration -- so the failure path stays safe.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/27f167e117eca310661fbcbacb352ea08face067
• https://git.kernel.org/stable/c/555d168bd98daa46daccc68c908201388c834293
• https://git.kernel.org/stable/c/8c869d5cf5affb20994bdbb60e7d46d65c91b55f
• https://git.kernel.org/stable/c/686c7a6af1eea8d2a919303e4c6bbec3de79dbdc
• https://git.kernel.org/stable/c/e1eee8f16628f8b6bcae0a366fd6a2dd65e71edd
• https://git.kernel.org/stable/c/d63f5a9f8121fb43c798056d7dd34c58f47185d7
• https://git.kernel.org/stable/c/0b349249d572633d7c8cdeb917623d1676a2b7c3
• https://git.kernel.org/stable/c/1e713f9bb2ac583521f06b0eb4e22440b1e3d078