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/sound/core/control.c b/sound/core/control.c
index 7e86a5b9f3b5..9768a3963c8f 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;
 }