Patch "ALSA: pcm: prevent UAF in snd_pcm_info" has been added to the 4.4-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ALSA: pcm: prevent UAF in snd_pcm_info

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     alsa-pcm-prevent-uaf-in-snd_pcm_info.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 362bca57f5d78220f8b5907b875961af9436e229 Mon Sep 17 00:00:00 2001
From: Robb Glasser <rglasser@xxxxxxxxxx>
Date: Tue, 5 Dec 2017 09:16:55 -0800
Subject: ALSA: pcm: prevent UAF in snd_pcm_info

From: Robb Glasser <rglasser@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 sound/core/pcm.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -149,7 +149,9 @@ 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;


Patches currently in stable-queue which might be from rglasser@xxxxxxxxxx are

queue-4.4/alsa-pcm-prevent-uaf-in-snd_pcm_info.patch