[PATCH] ALSA: pcm: prevent UAF in snd_pcm_info

From: Nick Desaulniers <ndesaulniers@google.com>
To: unlisted-recipients:; (no To-header on input)
Cc: keescook@chromium.org, Robb Glasser <rglasser@google.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>,
	Markus Elfring <elfring@users.sourceforge.net>,
	Takashi Sakamoto <o-takashi@sakamocchi.jp>,
	Arvind Yadav <arvind.yadav.cs@gmail.com>,
	alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org
Subject: [PATCH] ALSA: pcm: prevent UAF in snd_pcm_info
Date: Tue,  5 Dec 2017 09:16:55 -0800	[thread overview]
Message-ID: <20171205171657.74392-1-ndesaulniers@google.com> (raw)

From: Robb Glasser <rglasser@google.com>

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`.

Signed-off-by: Robb Glasser <rglasser@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 sound/core/pcm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sound/core/pcm.c b/sound/core/pcm.c
index 9070f277f8db..09ee8c6b9f75 100644
--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -153,7 +153,9 @@ 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;
-- 
2.15.0.531.g2ccb3012c9-goog
