sound: WARNING in snd_rawmidi_kernel_write1

[Dmitry Vyukov]

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);
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
snd_rawmidi_kernel_write1+0x4e1/0x780()
Modules linked in:
CPU: 1 PID: 27775 Comm: syz-executor Not tainted 4.5.0-rc1+ #305
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
00000000ffffffff ffff88003158f958[ 845.661205] ------------[ cut
here ]------------
WARNING: CPU: 3 PID: 27781 at sound/core/rawmidi.c:1181
snd_rawmidi_kernel_write1+0x4e1/0x780()
Modules linked in:
ffffffff82be11ad 0000000000000000
ffff880032138000 ffffffff87188ec0 ffff88003158f998 ffffffff813536d9
ffffffff8527ab31 ffffffff87188ec0 000000000000049d ffff8800321e4b88
Call Trace:
[< inline >] __dump_stack lib/dump_stack.c:15
[<ffffffff82be11ad>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
[<ffffffff813536d9>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482
[<ffffffff81353909>] warn_slowpath_null+0x29/0x30 kernel/panic.c:515
[<ffffffff8527ab31>] snd_rawmidi_kernel_write1+0x4e1/0x780
sound/core/rawmidi.c:1181
[<ffffffff8527cc93>] snd_rawmidi_write+0x543/0xb30 sound/core/rawmidi.c:1273
[<ffffffff817b7611>] do_loop_readv_writev+0x141/0x1e0 fs/read_write.c:719
[<ffffffff817bb478>] do_readv_writev+0x5f8/0x6e0 fs/read_write.c:849
[<ffffffff817bb696>] vfs_writev+0x86/0xc0 fs/read_write.c:886
[< inline >] SYSC_writev fs/read_write.c:919
[<ffffffff817be801>] SyS_writev+0x111/0x2b0 fs/read_write.c:911
[<ffffffff866531b6>] entry_SYSCALL_64_fastpath+0x16/0x7a
arch/x86/entry/entry_64.S:185
---[ end trace 35fa82e449e91fae ]---


On commit 26cd83670f2f5a3d5b5514a1f7d96567cdb9558b

[Takashi Iwai]

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;

[Dmitry Vyukov]

On Mon, Feb 1, 2016 at 11:36 AM, Takashi Iwai <ti...@suse.de> wrote:
> 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.

Missed this question. Here is it. I run qemu with "-soundhw all" flag.

0 [Dummy ]: Dummy - Dummy
Dummy 1
1 [Loopback ]: Loopback - Loopback
Loopback 1
2 [VirMIDI ]: VirMIDI - VirMIDI
Virtual MIDI Card 1
3 [port ]: MTPAV - MTPAV on parallel port
MTPAV on parallel port at 0x378
4 [pcsp ]: PC-Speaker - pcsp
Internal PC-Speaker at port 0x61
5 [Intel ]: HDA-Intel - HDA Intel
HDA Intel at 0xfebf0000 irq 24

But the patch helps with the warning message :)

[Takashi Iwai]

Ah, you enabled MTPAV driver. Please drop CONFIG_SND_MTPAV for your
testing. This is known to be unstable and is only for a dedicated
parport device, not meant as a generic device to be covered at all.


Takashi

[Dmitry Vyukov]

Dropped CONFIG_SND_MTPAV.