[PATCH 3.16 058/254] ALSA: pcm: prevent UAF in snd_pcm_info

Ben Hutchings
2018-02-28T16:02:38Z

From: Robb Glasser <rglasser@google.com>

commit 362bca57f5d78220f8b5907b875961af9436e229 upstream.

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@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
sound/core/pcm.c | 2 ++
1 file changed, 2 insertions(+)

--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -150,7 +150,9 @@ static int snd_pcm_control_ioctl(struct
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;