ALSA: pcm: prevent UAF in snd_pcm_info

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>

diff --git a/sound/core/pcm.c b/sound/core/pcm.c
index 13eaeb3..00905d1 100644 (file)
--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -145,7 +145,9 @@ static int snd_pcm_control_ioctl(struct snd_card *card,
                                err = -ENXIO;
                                goto _error;
                        }
                                err = -ENXIO;
                                goto _error;
                        }

+                       mutex_lock(&pcm->open_mutex);

                        err = snd_pcm_info_user(substream, info);
                        err = snd_pcm_info_user(substream, info);

+                       mutex_unlock(&pcm->open_mutex);

                _error:
                        mutex_unlock(&register_mutex);
                        return err;
                _error:
                        mutex_unlock(&register_mutex);
                        return err;