From 82fd4b05d704623a0e4aa7fda48e272a9889337d Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Tue, 14 Aug 2018 21:27:51 +0200 Subject: [PATCH] ALSA: seq: virmidi: Fix discarding the unsubscribed output The recent change to move the virmidi output processing to a work slightly modified the code to discard the unsubscribed outputs so that it works without a temporary buffer. However, this is actually buggy, and may spew a kernel warning due to the unexpected call of snd_rawmidi_transmit_ack(), as triggered by syzbot. This patch takes back to the original code in that part, use a temporary buffer and simply repeat snd_rawmidi_transmit(), in order to address the regression. Fixes: f7debfe54090 ("ALSA: seq: virmidi: Offload the output event processing") Reported-by: syzbot+ec5f605c91812d200367@syzkaller.appspotmail.com Signed-off-by: Takashi Iwai --- sound/core/seq/seq_virmidi.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/sound/core/seq/seq_virmidi.c b/sound/core/seq/seq_virmidi.c index a2f1c6b58693..cb988efd1ed0 100644 --- a/sound/core/seq/seq_virmidi.c +++ b/sound/core/seq/seq_virmidi.c @@ -149,8 +149,9 @@ static void snd_vmidi_output_work(struct work_struct *work) /* discard the outputs in dispatch mode unless subscribed */ if (vmidi->seq_mode == SNDRV_VIRMIDI_SEQ_DISPATCH && !(vmidi->rdev->flags & SNDRV_VIRMIDI_SUBSCRIBE)) { - while (!snd_rawmidi_transmit_empty(substream)) - snd_rawmidi_transmit_ack(substream, 1); + char buf[32]; + while (snd_rawmidi_transmit(substream, buf, sizeof(buf)) > 0) + ; /* ignored */ return; } -- 2.45.2