linux-kernel - Re: BUG: KASAN: use-after-free in snd_usb_audio

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Message-ID: <c0ebdec6-717a-c5d8-56e4-9b9a5a9e111d@osg.samsung.com>
Date:   Mon, 14 Nov 2016 09:55:54 -0700
From:   Shuah Khan <shuahkh@....samsung.com>
To:     Takashi Iwai <tiwai@...e.de>, Shuah Khan <shuahkhan@...il.com>
Cc:     alsa-devel@...a-project.org, LKML <linux-kernel@...r.kernel.org>,
        Shuah Khan <shuahkh@....samsung.com>
Subject: Re: BUG: KASAN: use-after-free in snd_usb_audio_free

On 11/14/2016 03:25 AM, Takashi Iwai wrote:
> 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;
>  }
> 

Hi Takashi,

The patch fixed the problem on 4.9-rc4. Didn't get a chance
to test it on 4.8.7.

thanks,
-- Shuah