ALSA: pcm: prevent UAF in snd_pcm_info
authorRobb Glasser <rglasser@google.com>
Tue, 5 Dec 2017 17:16:55 +0000 (09:16 -0800)
committerBen Hutchings <ben@decadent.org.uk>
Sat, 3 Mar 2018 15:50:44 +0000 (15:50 +0000)
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

index 13eaeb3..00905d1 100644 (file)
@@ -145,7 +145,9 @@ 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;