CVE-2026-89736usb: gadget: u_audio: Fix use-after-free on sound card disconnect

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/a7ecd1a04f4f485d7be6443d0f0b2c61a800cb82
• https://git.kernel.org/stable/c/f983793f03148b097977f200298db215cd2d4438
• https://git.kernel.org/stable/c/6f46762196f04464e1050a9ee94e72b917db9010
• https://git.kernel.org/stable/c/891a8d11f4d5eb50b2ce7570f4f98204a7a57493
• https://git.kernel.org/stable/c/c74ff0b1a0fca53d3ac185873c87d6a719b30a47
• https://git.kernel.org/stable/c/4e747c864a88537e18b1ffc19a1954c9686bb8e1
• https://git.kernel.org/stable/c/79a92896e2bb9471550c56fc23d8d93592f04c27
• https://git.kernel.org/stable/c/858965947081d10d41d9a1010a540d3d5eea958b