ALSA: Add a reference counter to card instance

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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/sound/core.h b/include/sound/core.h
index bc056687f647..93896ad1fcdd 100644
--- a/include/sound/core.h
+++ b/include/sound/core.h
@@ -132,6 +132,7 @@ struct snd_card {
         int shutdown;                   /* this card is going down */
         int free_on_last_close;         /* free in context of file_release */
         wait_queue_head_t shutdown_sleep;
+        atomic_t refcount;              /* refcount for disconnection */
         struct device *dev;             /* device assigned to this card */
         struct device *card_dev;        /* cardX object for sysfs */
 
@@ -189,6 +190,7 @@ struct snd_minor {
         const struct file_operations *f_ops;    /* file operations */
         void *private_data;             /* private data for f_ops->open */
         struct device *dev;             /* device for sysfs */
+        struct snd_card *card_ptr;      /* assigned card instance */
 };
 
 /* return a device pointer linked to each sound device as a parent */
@@ -295,6 +297,7 @@ int snd_card_info_done(void);
 int snd_component_add(struct snd_card *card, const char *component);
 int snd_card_file_add(struct snd_card *card, struct file *file);
 int snd_card_file_remove(struct snd_card *card, struct file *file);
+void snd_card_unref(struct snd_card *card);
 
 #define snd_card_set_dev(card, devptr) ((card)->dev = (devptr))