ALSA: 6fire: fix use-after-free on disconnect

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

ALSA: 6fire: fix use-after-free on disconnect

In usb6fire_chip_abort(), the chip struct is allocated as the card's

private data (via snd_card_new with sizeof(struct sfire_chip)). When

snd_card_free_when_closed() is called and no file handles are open, the

card and embedded chip are freed synchronously. The subsequent

chip->card = NULL write then hits freed slab memory.

Call trace:

usb6fire_chip_abort sound/usb/6fire/chip.c:59 [inline]

usb6fire_chip_disconnect+0x348/0x358 sound/usb/6fire/chip.c:182

usb_unbind_interface+0x1a8/0x88c drivers/usb/core/driver.c:458

...

hub_event+0x1a04/0x4518 drivers/usb/core/hub.c:5953

Fix by moving the card lifecycle out of usb6fire_chip_abort() and into

usb6fire_chip_disconnect(). The card pointer is saved in a local

before any teardown, snd_card_disconnect() is called first to prevent

new opens, URBs are aborted while chip is still valid, and

snd_card_free_when_closed() is called last so chip is never accessed

after the card may be freed.