CVE-2026-89736

In the Linux kernel, the following vulnerability has been resolved:

usb: gadget: u audio: Fix use-after-free on sound card disconnect

g audio cleanup() invokes snd card free when closed() to initiate sound card teardown and immediately frees the underlying struct snd uac chip context. However, snd card free when closed() returns asynchronously while ALSA control elements (kctls) remain open in userspace.

When userspace control applications access or close these open file descriptors, kctl callbacks attempt to dereference kctl->private data pointing to &uac->c prm or &uac->p prm within the freed uac structure, resulting in a use-after-free (UAF) memory corruption.

Fix this issue by deferring the destruction of struct snd uac chip until all references to the ALSA sound card are released. Register a custom card->private free callback (u audio card free) during g audio setup() that frees uac and its associated playback/capture request and ring buffers only when the sound card reference count drops to zero.