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, 11 insertions, 1 deletions

diff --git a/sound/firewire/bebob/bebob.c b/sound/firewire/bebob/bebob.c
index fc19c99654aa..b612599fb543 100644
--- a/sound/firewire/bebob/bebob.c
+++ b/sound/firewire/bebob/bebob.c
@@ -116,11 +116,19 @@ end:
 	return err;
 }
 
+/*
+ * 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
 bebob_card_free(struct snd_card *card)
 {
 	struct snd_bebob *bebob = card->private_data;
 
+	fw_unit_put(bebob->unit);
+
 	if (bebob->card_index >= 0) {
 		mutex_lock(&devices_mutex);
 		clear_bit(bebob->card_index, devices_used);
@@ -205,7 +213,7 @@ bebob_probe(struct fw_unit *unit,
 	card->private_free = bebob_card_free;
 
 	bebob->card = card;
-	bebob->unit = unit;
+	bebob->unit = fw_unit_get(unit);
 	bebob->spec = spec;
 	mutex_init(&bebob->mutex);
 	spin_lock_init(&bebob->lock);
@@ -310,6 +318,8 @@ static void bebob_remove(struct fw_unit *unit)
 
 	snd_bebob_stream_destroy_duplex(bebob);
 	snd_card_disconnect(bebob->card);
+
+	/* No need to wait for releasing card object in this context. */
 	snd_card_free_when_closed(bebob->card);
 }