Commit 82fd4b05 authored by Takashi Iwai's avatar Takashi Iwai

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: f7debfe5 ("ALSA: seq: virmidi: Offload the output event processing")
Reported-by: syzbot+ec5f605c91812d200367@syzkaller.appspotmail.com
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent f5b6c1fc
......@@ -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;
}
......
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