ALSA: seq: oss: Fix unbalanced use lock for synth MIDI device

commit f5e94b4c6ebdabe0f602d796e0430180927521a0 upstream.

When get_synthdev() is called for a MIDI device, it returns the fixed
midi_synth_dev without the use refcounting.  OTOH, the caller is
supposed to unreference unconditionally after the usage, so this would
lead to unbalanced refcount.

This patch corrects the behavior and keep up the refcount balance also
for the MIDI synth device.

Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/sound/core/seq/oss/seq_oss_synth.c b/sound/core/seq/oss/seq_oss_synth.c
index cd0e0ebbfdb1a1931b50f0fc9d70cdd08c17f740..9e2b250ae78059b22eb2e2160abee78eb8ae0ead 100644 (file)
--- a/sound/core/seq/oss/seq_oss_synth.c
+++ b/sound/core/seq/oss/seq_oss_synth.c
@@ -363,10 +363,14 @@ get_synthdev(struct seq_oss_devinfo *dp, int dev)
                return NULL;
        if (! dp->synths[dev].opened)
                return NULL;
-       if (dp->synths[dev].is_midi)
-               return &midi_synth_dev;
-       if ((rec = get_sdev(dev)) == NULL)
-               return NULL;
+       if (dp->synths[dev].is_midi) {
+               rec = &midi_synth_dev;
+               snd_use_lock_use(&rec->use_lock);
+       } else {
+               rec = get_sdev(dev);
+               if (!rec)
+                       return NULL;
+       }
        if (! rec->opened) {
                snd_use_lock_free(&rec->use_lock);
                return NULL;