Re: [PATCH] ALSA: pcm: prevent UAF in snd_pcm_info

[Takashi Iwai <tiwai@suse.de>]

On Tue, 05 Dec 2017 18:16:55 +0100,
Nick Desaulniers wrote:
> 
> From: Robb Glasser <rglasser@google.com>
> 
> When the device descriptor is closed, the `substream->runtime` pointer
> is freed. But another thread may be in the ioctl handler, case
> SNDRV_CTL_IOCTL_PCM_INFO. This case calls snd_pcm_info_user() which
> calls snd_pcm_info() which accesses the now freed `substream->runtime`.
> 
> Signed-off-by: Robb Glasser <rglasser@google.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

Looks reasonable.  Applied with Cc to stable now.


thanks,

Takashi

> ---
>  sound/core/pcm.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/sound/core/pcm.c b/sound/core/pcm.c
> index 9070f277f8db..09ee8c6b9f75 100644
> --- a/sound/core/pcm.c
> +++ b/sound/core/pcm.c
> @@ -153,7 +153,9 @@ static int snd_pcm_control_ioctl(struct snd_card *card,
>  				err = -ENXIO;
>  				goto _error;
>  			}
> +			mutex_lock(&pcm->open_mutex);
>  			err = snd_pcm_info_user(substream, info);
> +			mutex_unlock(&pcm->open_mutex);
>  		_error:
>  			mutex_unlock(&register_mutex);
>  			return err;
> -- 
> 2.15.0.531.g2ccb3012c9-goog
> 
>