UBUNTU-CVE-2026-89736: Use After Free

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: uaudio: Fix use-after-free on sound card disconnect gaudiocleanup() invokes sndcardfreewhenclosed() to initiate sound card teardown and immediately frees the underlying struct snduacchip context. However, sndcardfreewhenclosed() 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->privatedata pointing to &uac->cprm or &uac->pprm within the freed uac structure, resulting in a use-after-free (UAF) memory corruption. Fix this issue by deferring the destruction of struct snduacchip until all references to the ALSA sound card are released. Register a custom card->privatefree callback (uaudiocardfree) during gaudiosetup() that frees uac and its associated playback/capture request and ring buffers only when the sound card reference count drops to zero.