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

[Kees Cook]

On Tue, Dec 5, 2017 at 11:14 AM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> On Tue, 05 Dec 2017 18:16:55 +0100,
> Nick Desaulniers wrote:
>>
>> From: Robb Glasser <rglasser@xxxxxxxxxx>
>>
>> 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@xxxxxxxxxx>
>> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
>
> Looks reasonable.  Applied with Cc to stable now.

FWIW, this was assigned CVE-2017-0861. (Best to get it into the commit
log if possible.)

-Kees

>
>
> 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
>>
>>



-- 
Kees Cook
Pixel Security