[PATCH] ALSA: pcm: Fix snd_pcm_hw_params struct copy in compat mode

From: Nicolas Boichat
Date: Sun Jan 17 2016 - 22:49:50 EST


Running a kernel with KASan enabled, we spotted that the following
read in sound/soc/soc-pcm.c:soc_pcm_hw_params() is out of bounds:

/* copy params for each codec */
codec_params = *params;

The problem comes from sound/core/pcm_compat.c,
snd_pcm_ioctl_hw_params_compat, where we're copying from a
struct snd_pcm_hw_params to a struct snd_pcm_hw_params32:

/* only fifo_size is different, so just copy all */
data = memdup_user(data32, sizeof(*data32));

It turns out that snd_pcm_hw_params is 4 bytes longer than
snd_pcm_hw_params32, that's why an out-of-bounds read happens.

We separate kmalloc and memory copy operations to make sure
data has the correct length.

Signed-off-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
---
sound/core/pcm_compat.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c
index b48b434..9630e9f 100644
--- a/sound/core/pcm_compat.c
+++ b/sound/core/pcm_compat.c
@@ -255,10 +255,15 @@ static int snd_pcm_ioctl_hw_params_compat(struct snd_pcm_substream *substream,
if (! (runtime = substream->runtime))
return -ENOTTY;

- /* only fifo_size is different, so just copy all */
- data = memdup_user(data32, sizeof(*data32));
- if (IS_ERR(data))
- return PTR_ERR(data);
+ data = kmalloc(sizeof(*data), GFP_KERNEL);
+ if (!data)
+ return -ENOMEM;
+
+ /* only fifo_size (RO from userspace) is different, so just copy all */
+ if (copy_from_user(data, data32, sizeof(*data32))) {
+ err = -EFAULT;
+ goto error;
+ }

if (refine)
err = snd_pcm_hw_refine(substream, data);
--
2.6.0.rc2.230.g3dd15c0