ALSA: seq: Fix race at closing in virmidi driver

The virmidi driver has an open race at closing its assigned rawmidi
device, and this may lead to use-after-free in
snd_seq_deliver_single_event().

Plug the hole by properly protecting the linked list deletion and
calling in the right order in snd_virmidi_input_close().

BugLink: http://lkml.kernel.org/r/CACT4Y+Zd66+w12fNN85-425cVQT=K23kWbhnCEcMB8s3us-Frw@mail.gmail.com
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.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/seq/seq_virmidi.c b/sound/core/seq/seq_virmidi.c
index 3da2d48610b3..f71aedfb408c 100644
--- a/sound/core/seq/seq_virmidi.c
+++ b/sound/core/seq/seq_virmidi.c
@@ -254,9 +254,13 @@ static int snd_virmidi_output_open(struct snd_rawmidi_substream *substream)
  */
 static int snd_virmidi_input_close(struct snd_rawmidi_substream *substream)
 {
+        struct snd_virmidi_dev *rdev = substream->rmidi->private_data;
         struct snd_virmidi *vmidi = substream->runtime->private_data;
-        snd_midi_event_free(vmidi->parser);
+
+        write_lock_irq(&rdev->filelist_lock);
         list_del(&vmidi->list);
+        write_unlock_irq(&rdev->filelist_lock);
+        snd_midi_event_free(vmidi->parser);
         substream->runtime->private_data = NULL;
         kfree(vmidi);
         return 0;