ALSA: 6fire: Release resources at card release

The current 6fire code tries to release the resources right after the
call of usb6fire_chip_abort().  But at this moment, the card object
might be still in use (as we're calling snd_card_free_when_closed()).

For avoid potential UAFs, move the release of resources to the card's
private_free instead of the manual call of usb6fire_chip_destroy() at
the USB disconnect callback.

Fixes: c6d43ba ("ALSA: usb/6fire - Driver for TerraTec DMX 6Fire USB")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20241113111042.15058-6-tiwai@suse.de

Author: tiwai

sound/usb/6fire/chip.c

@@ -61,8 +61,10 @@ static void usb6fire_chip_abort(struct sfire_chip *chip)
 	}
 }
 
-static void usb6fire_chip_destroy(struct sfire_chip *chip)
+static void usb6fire_card_free(struct snd_card *card)
 {
+	struct sfire_chip *chip = card->private_data;
+
 	if (chip) {
 		if (chip->pcm)
 			usb6fire_pcm_destroy(chip);
@@ -72,8 +74,6 @@ static void usb6fire_chip_destroy(struct sfire_chip *chip)
 			usb6fire_comm_destroy(chip);
 		if (chip->control)
 			usb6fire_control_destroy(chip);
-		if (chip->card)
-			snd_card_free(chip->card);
 	}
 }
 
@@ -136,6 +136,7 @@ static int usb6fire_chip_probe(struct usb_interface *intf,
 	chip->regidx = regidx;
 	chip->intf_count = 1;
 	chip->card = card;
+	card->private_free = usb6fire_card_free;
 
 	ret = usb6fire_comm_init(chip);
 	if (ret < 0)
@@ -162,7 +163,7 @@ static int usb6fire_chip_probe(struct usb_interface *intf,
 	return 0;
 
 destroy_chip:
-	usb6fire_chip_destroy(chip);
+	snd_card_free(card);
 	return ret;
 }
 
@@ -181,7 +182,6 @@ static void usb6fire_chip_disconnect(struct usb_interface *intf)
 
 			chip->shutdown = true;
 			usb6fire_chip_abort(chip);
-			usb6fire_chip_destroy(chip);
 		}
 	}
 }