Re: WARNING in __snd_pcm_lib_xfer

[Takashi Iwai]

On Wed, 02 May 2018 04:12:02 +0200,
syzbot wrote:
> 
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    fff75eb2a08c Merge tag 'errseq-v4.17' of
> git://git.kernel.o...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?id=6530078334779392
> kernel config:
> https://syzkaller.appspot.com/x/.config?id=6493557782959164711
> dashboard link: https://syzkaller.appspot.com/bug?extid=1dac3a4f6bc9c1c675d4
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> userspace arch: i386
> syzkaller
> repro:https://syzkaller.appspot.com/x/repro.syz?id=5691583680741376
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+1dac3a4f6bc9c1c675d4@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> IPVS: ftp: loaded support on port[0] = 21
> WARNING: CPU: 1 PID: 4520 at sound/core/pcm_lib.c:2057
> pcm_sanity_check  sound/core/pcm_lib.c:2057 [inline]
...
>  snd_pcm_ioctl_compat+0xc96/0x1c90 sound/core/pcm_compat.c:716

OK, this is an easy one, just a forgotten PCM state check.
The patch below should fix it.


thanks,

Takashi

-- 8< --
From: Takashi Iwai <tiwai@xxxxxxx>
Subject: [PATCH] ALSA: pcm: Check PCM state at xfern compat ioctl

Since snd_pcm_ioctl_xfern_compat() has no PCM state check, it may go
further and hit the sanity check pcm_sanity_check() when the ioctl is
called right after open.  It may eventually spew a kernel warning, as
triggered by syzbot, depending on kconfig.

The lack of PCM state check there was just an oversight.  Although
it's no real crash, the spurious kernel warning is annoying, so let's
add the proper check.

Reported-by: syzbot+1dac3a4f6bc9c1c675d4@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
 sound/core/pcm_compat.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c
index 06d7c40af570..6491afbb5fd5 100644
--- a/sound/core/pcm_compat.c
+++ b/sound/core/pcm_compat.c
@@ -423,6 +423,8 @@ static int snd_pcm_ioctl_xfern_compat(struct snd_pcm_substream *substream,
 		return -ENOTTY;
 	if (substream->stream != dir)
 		return -EINVAL;
+	if (substream->runtime->status->state == SNDRV_PCM_STATE_OPEN)
+		return -EBADFD;
 
 	if ((ch = substream->runtime->channels) > 128)
 		return -EINVAL;
-- 
2.16.3