ACK: [SRU][Trusty][Artful][PATCH 1/1] ALSA: pcm: prevent UAF in snd_pcm_info

[Colin Ian King]

On 26/01/18 16:11, Kleber Sacilotto de Souza wrote:
> From: Robb Glasser <rglasser at 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`.
> 
> Note: this fixes CVE-2017-0861
> 
> Signed-off-by: Robb Glasser <rglasser at google.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers at google.com>
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai at suse.de>
> 
> CVE-2017-0861
> (cherry picked from commit 362bca57f5d78220f8b5907b875961af9436e229)
> Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
> ---
>  sound/core/pcm.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/sound/core/pcm.c b/sound/core/pcm.c
> index e1e9e0c999fe..5e95bc66f817 100644
> --- a/sound/core/pcm.c
> +++ b/sound/core/pcm.c
> @@ -150,7 +150,9 @@ 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;
> 

Clean cherry pick. Looks sane to me.

Acked-by: Colin Ian King <colin.king at canonical.com>