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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org,
        "Nick Desaulniers" <ndesaulniers@google.com>,
        "Takashi Iwai" <tiwai@suse.de>,
        "Robb Glasser" <rglasser@google.com>
Date:   Wed, 28 Feb 2018 15:20:18 +0000
Message-ID: <lsq.1519831218.452875324@decadent.org.uk>
Subject: [PATCH 3.16 058/254] ALSA: pcm: prevent UAF in snd_pcm_info
In-Reply-To: <lsq.1519831217.271785318@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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

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

From: Robb Glasser <rglasser@google.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@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 | 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;