From: Robb Glasser <rglasser@google.com>
Date: Tue, 5 Dec 2017 17:16:55 +0000 (-0800)
Subject: ALSA: pcm: prevent UAF in snd_pcm_info
X-Git-Tag: v4.4.106~88
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=659e7d2588f0fd970044fe00d9edeb482d375288;p=thirdparty%2Fkernel%2Fstable.git

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/sound/core/pcm.c b/sound/core/pcm.c
index 8e980aa678d0d..074363b63cc4e 100644
--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -149,7 +149,9 @@ 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;