ALSA: fireworks/bebob/dice/oxfw: add reference-counting for FireWire unit

Fireworks and Dice drivers try to touch instances of FireWire unit after
sound card object is released, while references to the unit is decremented
in .remove(). When unplugging during streaming, sound card object is
released after .remove(), thus Fireworks and Dice drivers causes GPF or
Null-pointer-dereferencing to application processes because an instance of
FireWire unit was already released.

This commit adds reference-counting for FireWire unit in drivers to allow
them to touch an instance of FireWire unit after .remove(). In most case,
any operations after .remove() may be failed safely.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Cc: <stable@vger.kernel.org> # 3.19+
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 10 insertions, 1 deletions

diff --git a/sound/firewire/dice/dice.c b/sound/firewire/dice/dice.c
index 90d8f40ff727..797f0726fc74 100644
--- a/sound/firewire/dice/dice.c
+++ b/sound/firewire/dice/dice.c
@@ -226,11 +226,19 @@ static void dice_card_strings(struct snd_dice *dice)
 	strcpy(card->mixername, "DICE");
 }
 
+/*
+ * This module releases the FireWire unit data after all ALSA character devices
+ * are released by applications. This is for releasing stream data or finishing
+ * transactions safely. Thus at returning from .remove(), this module still keep
+ * references for the unit.
+ */
 static void dice_card_free(struct snd_card *card)
 {
 	struct snd_dice *dice = card->private_data;
 
 	snd_dice_transaction_destroy(dice);
+	fw_unit_put(dice->unit);
+
 	mutex_destroy(&dice->mutex);
 }
 
@@ -251,7 +259,7 @@ static int dice_probe(struct fw_unit *unit, const struct ieee1394_device_id *id)
 
 	dice = card->private_data;
 	dice->card = card;
-	dice->unit = unit;
+	dice->unit = fw_unit_get(unit);
 	card->private_free = dice_card_free;
 
 	spin_lock_init(&dice->lock);
@@ -309,6 +317,7 @@ static void dice_remove(struct fw_unit *unit)
 
 	snd_dice_stream_destroy_duplex(dice);
 
+	/* No need to wait for releasing card object in this context. */
 	snd_card_free_when_closed(dice->card);
 }