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SubjectRe: [PATCH] ALSA: pcm: Fix snd_pcm_hw_params struct copy in compat mode
On Mon, 18 Jan 2016 04:49:18 +0100,
Nicolas Boichat wrote:
>
> 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@chromium.org>

Thanks for reporting. This is indeed effectively a revert of the
commit ef44a1ec6eee ('ALSA: sound/core: use memdup_user()'), which is
obviously wrong. Sigh, it's a really danger of such a "cleanup"
patch.

Could you rephrase the changelog mentioning the affecting commit and
resubmit?


Takashi

> ---
> 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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