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Subject[PATCH 1/2] ALSA: pcm: Fix snd_pcm_hw_params struct copy in compat mode
Date
This reverts one hunk of
commit ef44a1ec6eee ("ALSA: sound/core: use memdup_user()"), which
replaced a number of kmalloc followed by memcpy with memdup calls.

In this case, we are copying from a struct snd_pcm_hw_params32 to
a struct snd_pcm_hw_params, but the latter is 4 bytes longer than
the 32-bit version, so we need to separate kmalloc and copy calls.

This actually leads to an out-of-bounds memory access later on
in sound/soc/soc-pcm.c:soc_pcm_hw_params() (detected using KASan).

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
---
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

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