[alsa-devel] BUG: KASAN: use-after-free in snd_usb_audio_free

[Takashi Iwai]

On Sat, 12 Nov 2016 00:34:38 +0100,
Shuah Khan wrote:
> 
> Hi Takashi,
> 
> I am seeing the following use-after-free error when I disconnect an
> USB speaker. I saw this on 4.9-rc4 and 4.8.7. There might be race
> condition between the disconnect and pcm close perhaps.

Thanks, this looks like a new discovery.
Could you check whether the patch below works?


Takashi

---
diff --git a/sound/usb/card.c b/sound/usb/card.c
index 9e5276d6dda0..2ddc034673a8 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -315,7 +315,8 @@ static int snd_usb_audio_free(struct snd_usb_audio *chip)
 		snd_usb_endpoint_free(ep);
 
 	mutex_destroy(&chip->mutex);
-	dev_set_drvdata(&chip->dev->dev, NULL);
+	if (!atomic_read(&chip->shutdown))
+		dev_set_drvdata(&chip->dev->dev, NULL);
 	kfree(chip);
 	return 0;
 }