On Mon, 09 Apr 2018 17:25:15 +0200, Dmitry Vyukov wrote:
On Mon, Apr 9, 2018 at 5:18 PM, Takashi Iwai tiwai@suse.de wrote:
On Fri, 06 Apr 2018 02:02:02 +0200, syzbot wrote:
WARNING: CPU: 0 PID: 4468 at sound/core/pcm_native.c:620 snd_pcm_hw_params_choose sound/core/pcm_native.c:620 [inline]
This is a WARN_ON() to catch the inconsistent hw_params call. This shouldn't happen in theory, but the reality looks weirder.
The necessary "fix" is just to get rid of snd_BUG_ON(), but still wonder which condition it hits. If it's an empty parameter, the previous snd_pcm_hw_refine() should have caught and returned the error beforehand...
Hi Takashi,
The reproducer for this is trivially simple:
https://syzkaller.appspot.com/x/repro.syz?id=4913841943085056
(and I guess perf_event_open is red herring).
But the really important part there is probably this: Fault:true FaultCall:2 FaultNth:18 And you can see where it actually happened in the raw console log:
Raw console output: https://syzkaller.appspot.com/x/log.txt?id=6314122077536256
Does it explain things?
Yes, it does. So it's the kmalloc error from snd_pcm_hw_refine(). I overlooked this, as this kmalloc is relatively new, and that possibility wasn't considered in the WARN_ON() in question.
I'll rephrase the changelog text.
Thanks!
Takashi
In anyway this can't be a real crash, let's remove the warning to stop the chorus of syzbot birds.
thanks,
Takashi
-- 8< -- From: Takashi Iwai tiwai@suse.de Subject: [PATCH] ALSA: pcm: Remove WARN_ON() at snd_pcm_hw_params() error
snd_pcm_hw_params() may hit WARN_ON() when an inconsistent parameter set is passed. Although this should have been caught by the former snd_pcm_hw_refine() and returned the error, syzkaller succeeded to pass through and hit the WARN_ON(), which in turn made it panic unnecessarily.
For reducing this kind of noise, let's drop snd_BUG_ON() check.
Reported-by: syzbot+803e0047ac3a3096bb4f@syzkaller.appspotmail.com Signed-off-by: Takashi Iwai tiwai@suse.de
sound/core/pcm_native.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index b84554893fab..35ffccea94c3 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -617,7 +617,7 @@ static int snd_pcm_hw_params_choose(struct snd_pcm_substream *pcm, changed = snd_pcm_hw_param_first(pcm, params, *v, NULL); else changed = snd_pcm_hw_param_last(pcm, params, *v, NULL);
if (snd_BUG_ON(changed < 0))
if (changed < 0) return changed; if (changed == 0) continue;-- 2.16.3
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