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, 5 insertions, 1 deletions

diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
index ebf6e49ad3d4..7d4f62ab6711 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;
 }