linux-kernel - [PATCH 3.16 058/254] ALSA: pcm: prevent UAF in snd_pcm

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Date:   Wed, 28 Feb 2018 15:20:18 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Nick Desaulniers" <ndesaulniers@...gle.com>,
        "Takashi Iwai" <tiwai@...e.de>,
        "Robb Glasser" <rglasser@...gle.com>
Subject: [PATCH 3.16 058/254] ALSA: pcm: prevent UAF in snd_pcm_info

3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Robb Glasser <rglasser@...gle.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@...gle.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Ben Hutchings <ben@...adent.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;