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, 8 insertions, 2 deletions

diff --git a/sound/core/oss/mixer_oss.c b/sound/core/oss/mixer_oss.c
index 29f6ded02555..a9a2e63c0222 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;