ALSA: Add a reference counter to card instance

commit a0830dbd4e42b38aefdf3fb61ba5019a1a99ea85 upstream.

For more strict protection for wild disconnections, a refcount is
introduced to the card instance, and let it up/down when an object is
referred via snd_lookup_*() in the open ops.

The free-after-last-close check is also changed to check this refcount
instead of the empty list, too.

Reported-by: Matthieu CASTET <matthieu.castet@parrot.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

9 files changed, 76 insertions, 30 deletions

diff --git a/sound/core/control.c b/sound/core/control.c
index 819a5c579a3..699ccf54c01 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -86,6 +86,7 @@ static int snd_ctl_open(struct inode *inode, struct file *file)
 	write_lock_irqsave(&card->ctl_files_rwlock, flags);
 	list_add_tail(&ctl->list, &card->ctl_files);
 	write_unlock_irqrestore(&card->ctl_files_rwlock, flags);
+	snd_card_unref(card);
 	return 0;
 
       __error:
@@ -93,6 +94,8 @@ static int snd_ctl_open(struct inode *inode, struct file *file)
       __error2:
 	snd_card_file_remove(card, file);
       __error1:
+	if (card)
+		snd_card_unref(card);
       	return err;
 }
 
diff --git a/sound/core/hwdep.c b/sound/core/hwdep.c
index 75ea16f35b1..53a6ba5ad61 100644
--- a/sound/core/hwdep.c
+++ b/sound/core/hwdep.c
@@ -100,8 +100,10 @@ static int snd_hwdep_open(struct inode *inode, struct file * file)
 	if (hw == NULL)
 		return -ENODEV;
 
-	if (!try_module_get(hw->card->module))
+	if (!try_module_get(hw->card->module)) {
+		snd_card_unref(hw->card);
 		return -EFAULT;
+	}
 
 	init_waitqueue_entry(&wait, current);
 	add_wait_queue(&hw->open_wait, &wait);
@@ -148,6 +150,7 @@ static int snd_hwdep_open(struct inode *inode, struct file * file)
 	mutex_unlock(&hw->open_mutex);
 	if (err < 0)
 		module_put(hw->card->module);
+	snd_card_unref(hw->card);
 	return err;
 }
 
diff --git a/sound/core/init.c b/sound/core/init.c
index 3ac49b1b7cb..fa0f35b433d 100644
--- a/sound/core/init.c
+++ b/sound/core/init.c
@@ -212,6 +212,7 @@ int snd_card_create(int idx, const char *xid,
 	spin_lock_init(&card->files_lock);
 	INIT_LIST_HEAD(&card->files_list);
 	init_waitqueue_head(&card->shutdown_sleep);
+	atomic_set(&card->refcount, 0);
 #ifdef CONFIG_PM
 	mutex_init(&card->power_lock);
 	init_waitqueue_head(&card->power_sleep);
@@ -445,21 +446,36 @@ static int snd_card_do_free(struct snd_card *card)
 	return 0;
 }
 
+/**
+ * snd_card_unref - release the reference counter
+ * @card: the card instance
+ *
+ * Decrements the reference counter.  When it reaches to zero, wake up
+ * the sleeper and call the destructor if needed.
+ */
+void snd_card_unref(struct snd_card *card)
+{
+	if (atomic_dec_and_test(&card->refcount)) {
+		wake_up(&card->shutdown_sleep);
+		if (card->free_on_last_close)
+			snd_card_do_free(card);
+	}
+}
+EXPORT_SYMBOL(snd_card_unref);
+
 int snd_card_free_when_closed(struct snd_card *card)
 {
-	int free_now = 0;
-	int ret = snd_card_disconnect(card);
-	if (ret)
-		return ret;
+	int ret;
 
-	spin_lock(&card->files_lock);
-	if (list_empty(&card->files_list))
-		free_now = 1;
-	else
-		card->free_on_last_close = 1;
-	spin_unlock(&card->files_lock);
+	atomic_inc(&card->refcount);
+	ret = snd_card_disconnect(card);
+	if (ret) {
+		atomic_dec(&card->refcount);
+		return ret;
+	}
 
-	if (free_now)
+	card->free_on_last_close = 1;
+	if (atomic_dec_and_test(&card->refcount))
 		snd_card_do_free(card);
 	return 0;
 }
@@ -473,7 +489,7 @@ int snd_card_free(struct snd_card *card)
 		return ret;
 
 	/* wait, until all devices are ready for the free operation */
-	wait_event(card->shutdown_sleep, list_empty(&card->files_list));
+	wait_event(card->shutdown_sleep, !atomic_read(&card->refcount));
 	snd_card_do_free(card);
 	return 0;
 }
@@ -854,6 +870,7 @@ int snd_card_file_add(struct snd_card *card, struct file *file)
 		return -ENODEV;
 	}
 	list_add(&mfile->list, &card->files_list);
+	atomic_inc(&card->refcount);
 	spin_unlock(&card->files_lock);
 	return 0;
 }
@@ -876,7 +893,6 @@ EXPORT_SYMBOL(snd_card_file_add);
 int snd_card_file_remove(struct snd_card *card, struct file *file)
 {
 	struct snd_monitor_file *mfile, *found = NULL;
-	int last_close = 0;
 
 	spin_lock(&card->files_lock);
 	list_for_each_entry(mfile, &card->files_list, list) {
@@ -891,19 +907,13 @@ int snd_card_file_remove(struct snd_card *card, struct file *file)
 			break;
 		}
 	}
-	if (list_empty(&card->files_list))
-		last_close = 1;
 	spin_unlock(&card->files_lock);
-	if (last_close) {
-		wake_up(&card->shutdown_sleep);
-		if (card->free_on_last_close)
-			snd_card_do_free(card);
-	}
 	if (!found) {
 		snd_printk(KERN_ERR "ALSA card file remove problem (%p)\n", file);
 		return -ENOENT;
 	}
 	kfree(found);
+	snd_card_unref(card);
 	return 0;
 }
 
diff --git a/sound/core/oss/mixer_oss.c b/sound/core/oss/mixer_oss.c
index 18297f7f2c5..05395aaeaa3 100644
--- a/sound/core/oss/mixer_oss.c
+++ b/sound/core/oss/mixer_oss.c
@@ -52,14 +52,19 @@ static int snd_mixer_oss_open(struct inode *inode, struct file *file)
 					 SNDRV_OSS_DEVICE_TYPE_MIXER);
 	if (card == NULL)
 		return -ENODEV;
-	if (card->mixer_oss == NULL)
+	if (card->mixer_oss == NULL) {
+		snd_card_unref(card);
 		return -ENODEV;
+	}
 	err = snd_card_file_add(card, file);
-	if (err < 0)
+	if (err < 0) {
+		snd_card_unref(card);
 		return err;
+	}
 	fmixer = kzalloc(sizeof(*fmixer), GFP_KERNEL);
 	if (fmixer == NULL) {
 		snd_card_file_remove(card, file);
+		snd_card_unref(card);
 		return -ENOMEM;
 	}
 	fmixer->card = card;
@@ -68,6 +73,7 @@ static int snd_mixer_oss_open(struct inode *inode, struct file *file)
 	if (!try_module_get(card->module)) {
 		kfree(fmixer);
 		snd_card_file_remove(card, file);
+		snd_card_unref(card);
 		return -EFAULT;
 	}
 	return 0;
diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index 3cc4b86dfb7..f3cf781f8e1 100644
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -2457,6 +2457,8 @@ static int snd_pcm_oss_open(struct inode *inode, struct file *file)
       __error2:
       	snd_card_file_remove(pcm->card, file);
       __error1:
+	if (pcm)
+		snd_card_unref(pcm->card);
 	return err;
 }
 
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index e62da93da53..c67994d9955 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -1628,6 +1628,7 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
  _end:
 	write_unlock_irq(&snd_pcm_link_rwlock);
 	up_write(&snd_pcm_link_rwsem);
+	snd_card_unref(substream1->pcm->card);
 	fput(file);
 	return res;
 }
@@ -2100,7 +2101,9 @@ static int snd_pcm_playback_open(struct inode *inode, struct file *file)
 		return err;
 	pcm = snd_lookup_minor_data(iminor(inode),
 				    SNDRV_DEVICE_TYPE_PCM_PLAYBACK);
-	return snd_pcm_open(file, pcm, SNDRV_PCM_STREAM_PLAYBACK);
+	err = snd_pcm_open(file, pcm, SNDRV_PCM_STREAM_PLAYBACK);
+	snd_card_unref(pcm->card);
+	return err;
 }
 
 static int snd_pcm_capture_open(struct inode *inode, struct file *file)
@@ -2111,7 +2114,9 @@ static int snd_pcm_capture_open(struct inode *inode, struct file *file)
 		return err;
 	pcm = snd_lookup_minor_data(iminor(inode),
 				    SNDRV_DEVICE_TYPE_PCM_CAPTURE);
-	return snd_pcm_open(file, pcm, SNDRV_PCM_STREAM_CAPTURE);
+	err = snd_pcm_open(file, pcm, SNDRV_PCM_STREAM_CAPTURE);
+	snd_card_unref(pcm->card);
+	return err;
 }
 
 static int snd_pcm_open(struct file *file, struct snd_pcm *pcm, int stream)
diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
index ebf6e49ad3d..7d4f62ab671 100644
--- a/sound/core/rawmidi.c
+++ b/sound/core/rawmidi.c
@@ -379,8 +379,10 @@ static int snd_rawmidi_open(struct inode *inode, struct file *file)
 	if (rmidi == NULL)
 		return -ENODEV;
 
-	if (!try_module_get(rmidi->card->module))
+	if (!try_module_get(rmidi->card->module)) {
+		snd_card_unref(rmidi->card);
 		return -ENXIO;
+	}
 
 	mutex_lock(&rmidi->open_mutex);
 	card = rmidi->card;
@@ -440,6 +442,7 @@ static int snd_rawmidi_open(struct inode *inode, struct file *file)
 #endif
 	file->private_data = rawmidi_file;
 	mutex_unlock(&rmidi->open_mutex);
+	snd_card_unref(rmidi->card);
 	return 0;
 
  __error:
@@ -447,6 +450,7 @@ static int snd_rawmidi_open(struct inode *inode, struct file *file)
  __error_card:
 	mutex_unlock(&rmidi->open_mutex);
 	module_put(rmidi->card->module);
+	snd_card_unref(rmidi->card);
 	return err;
 }
 
diff --git a/sound/core/sound.c b/sound/core/sound.c
index 828af353ea9..f1889768774 100644
--- a/sound/core/sound.c
+++ b/sound/core/sound.c
@@ -99,6 +99,10 @@ static void snd_request_other(int minor)
  *
  * Checks that a minor device with the specified type is registered, and returns
  * its user data pointer.
+ *
+ * This function increments the reference counter of the card instance
+ * if an associated instance with the given minor number and type is found.
+ * The caller must call snd_card_unref() appropriately later.
  */
 void *snd_lookup_minor_data(unsigned int minor, int type)
 {
@@ -109,9 +113,11 @@ void *snd_lookup_minor_data(unsigned int minor, int type)
 		return NULL;
 	mutex_lock(&sound_mutex);
 	mreg = snd_minors[minor];
-	if (mreg && mreg->type == type)
+	if (mreg && mreg->type == type) {
 		private_data = mreg->private_data;
-	else
+		if (mreg->card_ptr)
+			atomic_inc(&mreg->card_ptr->refcount);
+	} else
 		private_data = NULL;
 	mutex_unlock(&sound_mutex);
 	return private_data;
@@ -275,6 +281,7 @@ int snd_register_device_for_dev(int type, struct snd_card *card, int dev,
 	preg->device = dev;
 	preg->f_ops = f_ops;
 	preg->private_data = private_data;
+	preg->card_ptr = card;
 	mutex_lock(&sound_mutex);
 #ifdef CONFIG_SND_DYNAMIC_MINORS
 	minor = snd_find_free_minor(type);
diff --git a/sound/core/sound_oss.c b/sound/core/sound_oss.c
index c7009204306..7442c7ac246 100644
--- a/sound/core/sound_oss.c
+++ b/sound/core/sound_oss.c
@@ -40,6 +40,9 @@
 static struct snd_minor *snd_oss_minors[SNDRV_OSS_MINORS];
 static DEFINE_MUTEX(sound_oss_mutex);
 
+/* NOTE: This function increments the refcount of the associated card like
+ * snd_lookup_minor_data(); the caller must call snd_card_unref() appropriately
+ */
 void *snd_lookup_oss_minor_data(unsigned int minor, int type)
 {
 	struct snd_minor *mreg;
@@ -49,9 +52,11 @@ void *snd_lookup_oss_minor_data(unsigned int minor, int type)
 		return NULL;
 	mutex_lock(&sound_oss_mutex);
 	mreg = snd_oss_minors[minor];
-	if (mreg && mreg->type == type)
+	if (mreg && mreg->type == type) {
 		private_data = mreg->private_data;
-	else
+		if (mreg->card_ptr)
+			atomic_inc(&mreg->card_ptr->refcount);
+	} else
 		private_data = NULL;
 	mutex_unlock(&sound_oss_mutex);
 	return private_data;
@@ -123,6 +128,7 @@ int snd_register_oss_device(int type, struct snd_card *card, int dev,
 	preg->device = dev;
 	preg->f_ops = f_ops;
 	preg->private_data = private_data;
+	preg->card_ptr = card;
 	mutex_lock(&sound_oss_mutex);
 	snd_oss_minors[minor] = preg;
 	minor_unit = SNDRV_MINOR_OSS_DEVICE(minor);