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ALSA: seq: virmidi: Fix discarding the unsubscribed output

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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: f7debfe540 ("ALSA: seq: virmidi: Offload the output event processing")
Reported-by: syzbot+ec5f605c91812d200367@syzkaller.appspotmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2018-08-14 21:27:51 +02:00
parent f5b6c1fcb4
commit 82fd4b05d7
1 changed files with 3 additions and 2 deletions
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5
sound/core/seq/seq_virmidi.c
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@ -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;
}