Affected: Linux

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

ALSA: core: Fix use-after-free in snd_card_do_free()

A use-after-free was detected in snd_card_do_free() when a sound card managed by devres is unbound while a user-space application still holds an open file descriptor.

For managed cards, the memory is allocated using devres_alloc(), and its release function is set to __snd_card_release(), which calls snd_card_free(). When the device is unbound, the unbind thread calls snd_card_free(), which drops a reference to the card's device. If the user thread still has an open file descriptor, the reference count does not reach zero, and the unbind thread blocks on wait_for_completion(&released).

When the user thread closes the file descriptor, it drops the final reference, invoking the device release callback release_card_device(), which calls snd_card_do_free(). snd_card_do_free() performs cleanup and calls complete(card->release_completion). This wakes up the unbind thread, which returns from snd_card_free() and __snd_card_release(). The devres core then immediately frees the memory block containing the snd_card structure.

Meanwhile, the user thread continues execution in snd_card_do_free() and evaluates `if (!card->managed)`. It reads the `managed` boolean from the snd_card structure that was just freed by the unbind thread, triggering a KASAN use-after-free.

Fix this by caching the value of card->managed in a local variable before calling complete(). This e…