linux-kernel - Re: sound: WARNING in snd_rawmidi_kernel

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Date:	Mon, 01 Feb 2016 11:36:59 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	"Dmitry Vyukov" <dvyukov@...gle.com>
Cc:	<alsa-devel@...a-project.org>, "Jaroslav Kysela" <perex@...ex.cz>,
	"LKML" <linux-kernel@...r.kernel.org>,
	"Alexander Potapenko" <glider@...gle.com>,
	"Kostya Serebryany" <kcc@...gle.com>,
	"syzkaller" <syzkaller@...glegroups.com>,
	"Sasha Levin" <sasha.levin@...cle.com>
Subject: Re: sound: WARNING in snd_rawmidi_kernel_write1

On Mon, 01 Feb 2016 11:15:08 +0100,
Dmitry Vyukov wrote:
> 
> Hello,
> 
> The following program triggers WARNING in snd_rawmidi_kernel_write1:
> 
> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> #include <unistd.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <sys/uio.h>
> #include <fcntl.h>
> 
> int main()
> {
>   int fd;
>   struct iovec iov;
> 
>   fd = open("/dev/snd/midiC3D0", O_RDWR);

What is the 3rd device?  Please show /proc/asound/cards content.


>   iov.iov_base = "";
>   iov.iov_len = 0;
>   writev(fd, &iov, 1);
>   return 0;
> }
> 
> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 27775 at sound/core/rawmidi.c:1181

The fix is easy, just remove snd_BUG_ON() like below.


thanks,

Takashi

---
diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
index a7759846fbaa..f75d1656272c 100644
--- a/sound/core/rawmidi.c
+++ b/sound/core/rawmidi.c
@@ -1178,7 +1178,7 @@ static long snd_rawmidi_kernel_write1(struct snd_rawmidi_substream *substream,
 	long count1, result;
 	struct snd_rawmidi_runtime *runtime = substream->runtime;
 
-	if (snd_BUG_ON(!kernelbuf && !userbuf))
+	if (!kernelbuf && !userbuf)
 		return -EINVAL;
 	if (snd_BUG_ON(!runtime->buffer))
 		return -EINVAL;